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Assessment of undephytinized and dephytinized rapeseed protein concentrate as sources of dietary protein for juvenile rainbow trout (Oncorhynchus mykiss)
Aquaculture Aquaculture 131 (1995) 261-277
Assessment of undephytinized and dephytinized rapeseed protein concentrate as sources of dietary protein for juvenile rainbow trout (Oncorhynchus
mykiss)
Z. TeskeredZC”, D.A. Higgsb,*, B.S. Dosanjhb, J.R. McBrideb, R.W. Hardy”, R.M. Beamesd, J.D. Jones’, M. Sirnell”, T. Vaarae, R.B. Bridges” aThe Institute
ofRuder Boskovic, Centre forMarine Research, Zagreb Laboratory for Aquaculture,
Bijenicka 54, 4100 Zagreb, Croatia “Fisheries and Oceans Canada, West Vancouver Laboratory, 4160 Marine Drive, West Vancouver, B.C., V7V IN6 Canada “Northwest Fisheries Science Center, 2725 Montlake Boulevard East, Seattle, WA 98112, USA ‘Department of Animal Science, University ofBritish Columbia, 248 2357 Main Mall, MacMillan Building, Vancouver, B.C., V6T 2A2 Canada ‘Alko Ltd., Process and Product Development, SF 05200, Rajamiiki, Finland
Accepted 3 October 1994
Abstract This study was undertaken to evaluate three sources of rapeseed protein concentrate (RPC) as partial or total replacements of steam-dried whole herring meal (HM) in a practical diet for juvenile rainbow trout. Groups of 4.2-4.4 g trout held in lO.O-10.3”C well water on a natural photoperiod were fed one of 10 isonitrogenous (43% protein) and isoenergetic (21.6 MJ gross energy/kg) diets to satiation 3 times daily. Each of three test protein sources, viz. undephytinized, untreated control RPC (UDC) , undephytinized solvent-treated control RPC (UDSC) , and dephytinized RPC (DP), comprised about 19.0, 39.0 and 59.0% respectively of dietary protein by replacement of one-third (L), two-thirds (M) and all (H) of the HM protein in the control diet. Rainbow trout growth rate, feed intake, feed efficiency, protein and gross energy utilization, mortality and health were not compromised when either UDC or DP replaced up to 66% of HM protein in the control diet. Total replacement of HM protein with each of the RPC sources did not depress feed intake, but did significantly reduce growth rate, feed efficiency, and protein and energy utilization. The procedure *Corresponding author. ‘This paper is dedicated to the memory of Dr. John D. Jones, formerly of the Food Research Centre, Central Experimental
Farm, Ottawa, ON KlA OC6, Canada.
0044~8486/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDIOO44-8486(94)00334-3
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used to dephytinize RPC lowered RPC protein quality. Whole body concentrations of calcium and phosphorus were inversely related to the dietary levels of UDC and UDSC. Body levels of zinc were significantly depressed in fish fed the diet with UDSC-H. Fish fed diets with DP displayed normal mineral levels. Significant elevation of thyroid follicle epithelial cell heights was found only in those groups fed the diets with UDC-H or UDSC-H. Whole body proximate composition was generally uninfluenced by diet treatment. It is concluded that RPC can comprise 39% of the dietary protein (fish meal only I 1%) for rainbow trout without adversely affecting performance. Nutritional strategies that may enable complete replacement of fish meal protein in diets for rainbow trout by RPC are outlined. Keywords: Rapeseed protein concentrate; Oncorh.ynchus mykiss; Feeding and nutrition-fish,
dietary value
1. Introduction Feed accounts for 40-60% of the operating costs of salmon farms, with almost two-thirds of the feed cost originating from the protein sources (Higgs, 1986; Higgs et al., 1995a). High-quality fish meals are used extensively ( > 50% of diet) in formulated salmon diets to meet the high dietary protein requirements of farmed salmon in seawater (Higgs et al., 1995b). This practice largely accounts for the high cost of the protein moiety of salmon feeds. Fish meals, however, can vary markedly in quality and price (McCallum and Higgs, 1989; Pike et al., 1990; Clancy, 1992). In addition, future supplies of fish meal will probably be lower and prices higher than at present (Barlow, 1989; Rumsey, 1993; Higgs et al., 1994a). Consequently, future fish farming production costs will probably increase unless suitable inexpensive alternative protein sources that are of consistently high quality are identified and/or developed. Canola is the name given to genetically selected varieties of rapeseed of the Brussica naps and B. campestris species that are low in both glucosinolates or antithyroid factors ( < 30 pmol of alkenyl glucosinolates per gram of oil-free dry matter of seed) and erucic acid ( < 2% of total fatty acids in the oil) (Bell, 1993). The amount of rapeseed/canola protein potentially available for inclusion in animal diets exceeds the annual global production of fish meal protein (Higgs et al., 1995a). Further, the cost of canola meal expressed in US $/kg protein is presently 63.5% of that of Chilean anchovy meal (0.47 versus 0.74 $/kg protein) (Higgs et al., 1994). The quality of rapeseed/canola protein has also been judged by Higgs et al. (1988, 1990) to be equivalent to that of whole herring meal and higher than that of soybean meal and cottonseed meal using the essential amino acid index approach of Oser ( 1959). Complete realization of the high quality of rapeseed/canola protein is compromised by the presence of antinutritional factors. Some of these are common to all oilseed protein products, e.g. fiber, carbohydrates, phenolic compounds and phytic acid. Others are unique, e.g. glucosinolates (Higgs et al., 1995a). Rapeseed/canola protein concentrates, relative to canola meal, contain reduced levels of glucosinolates, fiber, nitrogen-free extract, and phenolic constituents, e.g. sinapine and tannins. Also, they have significantly higher levels of digestible protein and energy for salmonids (Hajen et al., 1993; Higgs et al., 1994, 1995a). By contrast, the concentrates have higher levels of phytic acid (5.3-7.5%; Erdman,
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263
1979; Jones, 1979) than the meals (3.1-3.7%; Cheryan, 1980; McCurdy and March, 1992). Phytic acid, the hexaphosphate of myoinositol, is strongly negatively charged at all pH values normally encountered in feed. This compound has strong affinity for proteins at low pH and for cations such as zinc at intestinal pH’s. High dietary levels of phytic acid may depress growth, feed efficiency, bioavailability of protein and zinc as well as thyroid function in salmonids (Spinelli et al., 1983; Richardson et al., 1985). Previous research with juvenile rainbow trout (Yurkowski et al., 1978) and chinook salmon (Higgs et al., 1982) showed that rapeseed protein concentrate (RPC) may comprise more than 24% of the dietary protein by replacement of fish meal. Neither of these studies, however, established the upper limits of RPC that could be substituted for fish meal without compromising fish performance. Also, no attempt was made in these studies to assess whether the nutritive value of RPC could be improved by dephytinization (removal of its phytic acid content). In this study, we evaluated the merits of three sources of RPC (undephytinized, untreated control; undephytinized, solvent-treated control; dephytinized) as partial or total replacements of steam-dried whole herring meal in a practical diet for rainbow trout.
2. Materials and methods Fish and experimental conditions In January, 1990, Spring Valley rainbow trout (Oncorhynchus rnykiss) were selected for uniform size (mean weight + 1 s.d.). Then they were distributed randomly into 20 800liter fibreglass tanks so that each contained 74-77 trout (range in initial mean weight, 4.24.4 g). All groups were held in flowing (7.5 l/min), [email protected]”C well water on a natural photoperiod for the duration of the study (84 days). Dissolved oxygen content of the water during the experiment ranged from 9.9-10.6 mg/l. Diets and feeding protocol Ten dry diets (control diet based upon University of Guelph trout formulations, Hilton and Slinger, 1981) of equivalent protein, lipid and gross energy content (43%, 18% and 21.6 MJ/kg on a dry weight basis, respectively) were prepared according to Higgs et al. (1979). The diets were distinguished on the basis of the control and test protein sources employed (i.e. steam-dried whole herring meal HM; undephytinized untreated control RPC, UDC; undephytinized, solvent-treated control RPC, UDSC; and dephytinized RPC, DP) and according to the level of replacement of HM protein in the control diet (i.e. one-third, L; two-thirds, M; and total, H replacement). Thus, DP-M signifies that dephytinized RPC replaced 66% of the HM protein in the control diet. Each of the three test sources of RPC (Bronowski FRI-73-5 (343) ) comprised about 19.0, 39.0 and 59% of the dietary protein as the HM protein in the control diet was removed progressively (Table 1). UDSC was included in the experiment to determine whether the incubation and drying conditions that were used during the dephytinization process influenced the quality of the RPC protein (negative control). The dietary mineral levels were generally equalized in each case (Table 2) by preparing separate mineral supplements following analysis of each protein source for mineral content by plasma emission spectroscopy (Higgs et al., 1982). All diets were
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Table 1 Ingredient composition and protein, lipid and energy contents of test diets fed to juvenile rainbow trout for 84 days Ingredient
Herring meal Rapeseed protein concentrate Undephytinized Dephytinized Undephytinized, solvent control Wheat middlings Herring oil (stabilized)’ Lx.-Methionine L-Lysine Santoquin CaHPO, CaCO, Constant components” Protein (%) Lipid (%) Gross energy (MJ/kg)’ Metabolizable energy’
Diet (g/kg dry weight)” HM”
UDC-L UDC-M UDC-H DP-L
DP-M
DP-H
320
213.3
106.7
-
213.3
106.7
-
213.3
106.7
_ _
121.1 _
242.2 _
363.3 _
130.1
260.2
-
-
_
~390.3
_ _ _ _ 169.5 140.0 189.6 152.7 115.5 123.2 127.0 118.8 121.1 123.4 3.99 4.00 3.40 3.94 3.84 _ _ 1.40 1.30 0.012 0.037 0.062 0.086 0.037 0.063 0.088 _ 12.4 15.9 18.3 12.8 17.4 20.5 _ _ 6.6 13.9 6.0 13.1 33 1.9 331.9 331.9 331.9 331.9 331.9 331.9 45.1 43.3 41.9 42.3 45.3 42.0 43.1 17.8 17.8 18.1 18.6 17.7 18.0 18.1 22.2 21.7 21.4 21.7 22.0 21.3 21.5 17.1 16.7 16.6 16.8 17.0 16.5 16.7 _
228.04 116.5 3.54
197.7 120.0 3.58 _
UDSC-L UDSC-M UDSC-H
126.5 193.4 118.7 3.40 0.037 12.7 331.9 43.0 17.7 21.5 16.6
253.0 160.6 120.9 3.88 _ 0.063 16.3 6.7 331.9 42.2 18.0 21.4 16.6
379.5 127.2 123.1 3.88 1.38 0.088 18.9 14.2 331.9 43.6 17.8 21.6 16.7
6.8 0.8
12.0 1.6
19.0 2.5
(MJk) Inositol phosphate (IPY (wmol/g) IP6 IP5
1.8 0
6.5 0
13.0 0
18.0 1.7
2.0 0
2.2 0.4
1.8 0
The diets have been distinguished on the basis of the control and test protein sources employed and the level of herring meal replaced in the control (HM) diet. “Steam-dried whole herring meal stabilized with 250 mg ethoxyquin/kg. hHM = herring meal; UDC = undephytinized, untreated control RPC; DP = dephytinized RPC; UDSC = undephytinized, solvent-treated control RPC. The letters L, M and H refer respectively to 4, 3 and complete replacement of herring meal protein with the test protein source. ‘Stabilized with 0.5 g santoquin/kg oil. “Common dietary components (g/kg dry diet) were as follows: poultry by-product meal, 70; blood meal, 40; corn gluten meal, 65; dried whey, 60; vitamin/mineral supplement, 50; choline chloride (60%), 5; ascorbic acid, 2; permapell, 9.92; FinnstimTM715.7de&in, 15. The vitamin supplement supplied the following levels of nutrients/kg dry diet: vitamin A acetate, 5000 IU; cholecalciferol ( Dz), 2400 IU; m-ol-tocopheryl acetate (E), 300 IU; menadione, 18 mg; o-calcium pantothenate, 192.5 mg; pyridoxine HCI, 49.3 mg; riboflavin, 60 mg; niacin, 300 mg; folic acid, 15 mg; thiamine mononitrate, 56 mg; biotin, 1.5 mg; cyanocobalamin (B ,*), 0.09 mg; inositol, 400 mg. Refer to Table 2 for the composition of the mineral supplements. ‘Estimated by ascribing 0.0236 MJ/g protein, 0.0395 MJ/g lipid and 0.0172 M.J/g carbohydrate (Higgs et al., 1995b). ‘Estimated by ascribing0.0188 MJ/g protein, 0.0356 MJ/g lipid, 0.0159 MJ/g animal carbohydrate, 0.0134 MJ/g dextrin and 0.00669 MJ/g raw starch (Higgs et al., 1983; Beamish et al., 1986). xIP4 and IP3 were not detected.
3322 5 4.5 2.8 0.2 5
_
2632 763 1007 6.5 46 109 75 995 566
HM
DieP
1365 1365 1365 5 4.5 2.7 0.2 5
1082 1082 1478 5 4.5 2.8 0.2 5 1056 1056 1671 5 4.5 2.8 0.2 5
482 6.4 72 107 64 2052 _
2911 1324 _
_
3768
DP-L
1412 1412 1412 5 4.5 2.9 0.2 5
275 6.3 98 104 52 2543
5114 2418 3950 1119
DP-M
and > 0.06% magnesium
1502 1502 1502 5 4.5 2.7 0.2 5
442 6.8 119 102 38 3522
5403 5573 4174 1190
UDC-H
phosphorus
275 6.6 94 104 50 2868 _
4675 2639 3613 1081 _
UDC-M
1108 1108 1520 5 4.5 2.8 0.2 5
408 6.3 74 107 64 2228
2893 1204
3744 _
UDSC-L
1383 1383 1383 5 4.5 2.7 0.2 5
215 6.2 101 105 52 2896 _
4790 2695 3702 1096 _
UDSC-M
1521 1521 1521 5 4.5 2.7 0.2 5
442 6.0 130 103 41 3563
5559 5669 4294 1205
UDSC-H
from animal sources and the mineral supplement.
1565 1565 1565 5 4.5 2.9 0.2 5
442 6.2 124 102 41 3034
6039 5260 4666 1240 _
DP-H
in the test diets, expected levels of dietary minerals and means of the dietary concentrations
350 6.5 67 106 62 2214
2818 1171 _
3648
UDC-L
employed
“Refer to Table 1 for diet designations. “All diets were formulated to have 2 0.7% inorganic ‘Not determined.
K (as KzSW (as WW (as KH,PO,) I (as KIOa) F(asNaF) Co (as CoC1,.6H,O) Se (as Na,SeOl) Al (as AlC13.6H20)
Ca (as CaHPO,) (as CaCO,) P (as CaHPO,) (as KH,P04) ( as N&PO,. H,O) Mg (as MgSO,.7H,O) Cu (as CuS04.5Hz0) Fe (as FeS04.7H,0) Zn (as ZnSO,.7H,O) Mn (as MnSO,.H,O) Na (as NaCl) (asNaH,PO, . H,O)
Mineral
Table 2 Composition of mineral supplements (mg/kg dry diet)
15 24.5 3 to.2 >5
8024
200tX3315b 15 335 150 90 4600
13675h
15495
Expected total
as determined
ND
ND” 20.2
25 24.5
7331
25684332 19 364 237 100 5642
15634
17442
Determined level
by analysis
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formulated to have 2 0.7% inorganic phosphorus (P) and 2 0.06% magnesium (Mg) from animal and inorganic sources (Lall, 1989). The mean dietary concentrations of minerals as determined by plasma spectroscopy are provided in Table 2. Since Yurkowski et al. ( 1978) had previously noted significant depression of feed intake in trout when fish meal was replaced totally by RPC in the absence of diet palatability enhancers, all diets were supplemented with 1.5% FinnstimTM. FinnstimTM contains 94% betaine (anhydrous) in combination with 3% of an L-amino acid mixture that is mainly alanine, serine, isoleucine, leucine, valine and glycine (Clarke et al., 1994). Betaine and L-amino acids are thought to act as diet palatability enhancers (Mackie and Mitchell, 1985), and it was hoped that the FinnstimTM would counteract any suppression of feed intake that might occur in trout fed diets in which fish meal was partially or totally replaced by RPC. On the basis of published values for the amino acid compositions of protein sources other than RPC (NRC, 1983) and analyzed values for UDC and DP ( AAA Laboratory, Mercer Island, WA, USA), it was estimated that the diets met or exceeded the known indispensable amino acid needs of rainbow trout as provided by Ogino ( 1980)) Cho ( 1990)) and Higgs et al. ( 1995b). All groups were fed their assigned diet by hand 3 times daily until the point of satiety. Feed wastage was negligible at each feeding time (08.00-09.30, 11 .OO-12.00, and 15.0016.00 h). Diet pellet size was based upon the recommendations of Hilton and Slinger ( 198 1) . The daily feed intake and mortality of each group were recorded. Fish weighing, sampling and chemical and histological analyses All fish were removed from their respective tanks every 21 days following a minimum of 17 h of food deprivation. Sixty fish, selected at random from each group, were anaesthetized (2 phenoxyethanol, 0.33 ml/l) and individually weighed (nearest 0.01 g) and measured (fork length, nearest 0.1 cm). The fish were fed to satiation once on each weighing day between 15.00 and 16.00 h. Four samples of 9 fish were analyzed for initial whole body proximate and mineral compositions. Ten fish were removed randomly from each replicate (tank) on day 84 for determination of final whole body proximate and mineral compositions (5 pools of 2 fish each per replicate). Three fish were sampled from each replicate on day 85 for histological examination of the liver, kidney, thyroid and alimentary tract. Whole body and diet proximate compositions were determined according to the procedures outlined by Higgs et al. ( 1979). Carcass mineral compositions were determined using plasma emission spectroscopy (Higgs et al., 1982). Total levels of glucosinolates in UDC, DP and UDSC were assayed according to the thymol procedure of Tholen et al. ( 1989). Dietary glucosinolate contents were calculated and expressed as pmollkg dry diet. Dietary levels of inositol phosphates were determined using the procedures of Sandberg et al. ( 1987). Histological examinations of the selected tissues mentioned above were conducted according to the methods of McBride and Van Overbeeke ( 197 1) and Van Overbeeke and McBride ( 197 1) . RPC dephytinization Dephytinization of RPC was conducted by Alko Ltd. (Rajarnaki, Finland) according to the following protocol. Ten kg of RPC were suspended in 100 liters of water. The pH was adjusted to 5.0 and then Finase S 2X was added at a dosage of 5000 phytase units (PU) /g
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RPC ( 1 PU = amount of enzyme that liberates 1 nmol of inorganic phosphate from sodium phytate in 1 min under standard conditions of pH 5.0 and temperature of 37°C). The suspension was incubated at 55°C for 4 h, cooled and lyophilized. Control RPC (UDSC) was treated similarly, but Finase S 2X was not added. Data
calculation
and analysis
With respect to calculation of specific growth rates (SGR;% wet weight/day), the fish wet weights at each sample time were transformed to log,. Thereafter, they were subjected to a hierarchical analysis of covariance with replicates (random) nested in diets, time as the covariate and different covariate slopes allowed for each diet. Subsequently, SGR were derived from the covariate slopes as follows: SGR = ( eslope- 1) X 100. Scheffe’s test with P = 0.05 was used to detect any significant differences between the covariate slopes. Feed intake (% body weight/day) was calculated for each 21-day interval by dividing the mean daily dry feed intake per fish X 100 by the geometric mean wet weight of the fish (Richardson et al., 1985). Feed efficiency (FE) and protein efficiency ratio (PER) were calculated, respectively, as wet weight gain/dry feed or protein intake. Percent protein deposited (PPD) was calculated as protein gain X loo/protein intake. Gross energy conversion efficiency (GECE) was calculated in a similar fashion. The combustible energy values that were used for protein, lipid and carbohydrate were 0.0236 MJ/g protein, 0.0395 MJ/g lipid and 0.0172 MJ/g carbohydrate (Higgs et al., 1995b). The values for protein and lipid were used when estimating body energy content. To determine thyroid follicle epithelial cell heights (TFECH), 5 measurements were taken on each of the 5 follicles per fish. Data for feed intake, FE, PER, PPD, GECE, TFECH and levels of whole body proximate constituents and minerals were analyzed by one-way ANOVA with replicate nested in diet Table 3 Feed intake (mean daily dry feed intake per fish X 100 + geometric mean wet weight of fish) of juvenile rainbow trout during each 21-day interval of an 84-day study in relation to diet treatment Diet”
HM UDC-L UDC-M UDC-H DP-L DP-M DP-H UDSC-L UDSC-M UDSC-H “Refer to bOne-way P
Feed intake (%/day)b o-21
2142
42-63
63-84
4.38 4.48 4.31 4.20 4.14 4.28 4.44 4.04 4.44 4.34
4.1gab 3.13” 4.10ab 4.69b 4.01ab 4.02”b 4.4Y 4.01ab 4.7@ 4.71b
4.13a 3.61” 3.78” 4.60ab 3.91a 3.99” 4.28” 3.68” 4.06” 5.00b
3.67ab 3.34” 3.43” 4.54cd 3.48” 3.71ab 4.373.36” 3.87”” 5.04d
Table 1 for diet designations. ANOVA with replicate nested in diet and replicate treated as random indicated P> 0.05 (days O-21 ) , (days 21-42). P
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I31 (1995) 261-277
RATE
3
2.5
O/o
i
d.e,f
OHM
c _
UDC
-DP
mUDSC
e,f
2
/
1.5 ii Y
’ 0.5
0 Y
FEED EFFICIENCY 0.8 0.7
I
UDC
-DP
mUDSC
ad-
0.6
/
0.4
g
0.3 0.2 0.1
g
0.50
HM
L
M
H
L
M
H
L
M
H
DIET
Fig. 1. Specific growth rates (% wet weight/day) and feed efticiencies (wet weight gain/dry feed intake) of rainbow trout between day 0 and 84 in relation to diet treatment. See Table 1 for diet designations. Diet treatment significantly influenced growth rates (P < 0.0001) and feed efficiencies (P < 0.0001) . Refer to “Materials and methods” for details of statistical analyses of data.
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131 (1995) 261-277
269
RATIO
1.8 1.6
DP
m
DP
mUDSC
UDSC
1.4 1.2 9
b
b
1 / 0.8 it 9
0.6 0.4 0.2 I
0,
PERCENT PROTEIN DEPOSITED 30
r UDC
-
25
20
O/o
‘5
10
5
r-l HM
L
M
H
L
M
H
L
M
H
DIET Fig. 2. Overall protein efficiency ratios (body weight gain (g) /protein intake (g)) and percentages of dietary protein deposited [protein gainX loo/protein intake (g) I for rainbow trout in relation to diet treatment. Diet treatment significantly influenced both indices of protein utilization (P < 0.001). Refer to Table 1 and “Materials and methods” for additional information.
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and replicate treated as random or by two-way ANOVA with replicate nested in each test protein source by replacement level combination (HM treatment deleted). Where appropriate, Neumann-Keuls test with P = 0.05 was used to detect significant differences among treatment means.
3. Results Values for SGR, feed intake, FE, protein utilization (PER and PPD), GECE and mortality ( < 3% of initial number in each group) of trout were not compromised when either UDC or DP replaced up to 66% of the HM protein in the control diet (Table 3; Figs. 1,2 and 3). Best overall performance (growth, FE, PER, PPD, GECE) was observed for fish fed diet UDC-L. No aberrations were noted in the histological structure of the liver, kidney, thyroid and alimentary tract, irrespective of diet treatment. Feed intake was not depressed when each of the test RPC sources replaced all of the HM protein in the control diet (Table 3). Also, feed intake was generally unaffected by the test sources of RPC but was, in contrast, directly related to the level of replacement of HM
GROSS ENERGY CONVERSION EFFICIENCY 35
r I
CJHM
30
UDC
-DP
~UDSC
d d
25
HM
L
M
H
L
M
H
L
M
H
DIET Fig. 3. Overall gross energy conversion efficiencies (gross energy gain X loo/energy intake) in relation to diet treatment. Diet treatment significantly influenced energy utilization (P < 0.0001). Refer to Table 1 and “Materials and methods” for additional information.
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ASH
3 OHM
UDC
=DP
mUDSC
2.5
2
o/o
1.5
1
0.5
0
LIPID
16 OHM
UDC
-DP
mUDSC
14 b
b
%
8 6
HM
L
M
H
H
L
M
H
Fig. 4. Final whole body percentages of ash and lipid (wet weight basis) in rainbow trout in relation to diet treatment. Diet treatment significantly affected ash and lipid percentages (P < 0.01 in each case). Percentages for whole body protein and moisture were uninfluenced by diet. Refer to Table 1 and “Materials and methods” for additional information.
212 Table 4 Final concentrations
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of selected minerals in the whole bodies of rainbow trout in relation to diet treatment
Diet”
Element (mg/kg
HM UDC-L UDC-M UDC-H DP-L DP-M DP-H UDSC-L UDSC-M UDSC-H
dry weight)b
Ca
P
Zn
17505 16027 14423 13822 17725 16494 17323 17037 16661 13975
15564 14501 13480 13292 15845 14963 15460 15221 15115 13427
115” 101”” 107”b 105”b 116b 114b 122” 115b 107a” 918
‘Refer to Table 1 for diet designations. “ANOVA indicated P< 0.05 for each element. Within a column, diet groups with the same superscript letter were not significantly different (Neumann-Keuls test with P = 0.05).
THYROID FOLLICLE EPITHELIAL CELL HEIGHT 20 OHM
UDC
-DP
mUDSC
b
P m 1C
HM
L
M
H
L
M
H
L
M
H
DIET Fig. 5. Final thyroid follicle epithelial cell heights (TFECH) for rainbow trout in relation to diet treatment. Diet treatment had a significant influence on TFECH (P < 0.05). Refer to Table 1 and “Materials and methods” for additional information.
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213
protein (two-way ANOVA). Thus, trout fed diets in which all of the HM protein had been replaced by RPC, irrespective of source, exhibited the highest feed intakes, especially after day 21 (Table 3). Performance indices, other than feed intake, were significantly reduced when fish meal was totally replaced by each of the RPC sources. Also, trout fed diet UDSC-H exhibited a significantly poorer performance than those fed diets UDC-H and DP-H (Figs. 1, 2 and 3; two-way ANOVA). Diet treatment did not significantly influence whole body moisture (range in mean values 7 1.2-72.6%) and protein (range in mean values 14&15.3%). Percentages of ash, however, were significantly lower in trout consuming diet UDC-H relative to those for fish fed all other diets except diets UDC-M and UDSC-H. Also, whole body lipid was lower in fish fed diet DP-L than in those fed all other diets except HM, DP-H and UDSC-H (Fig. 4). All other differences were not significant. Final whole body concentrations of calcium (Ca) , P and zinc (Zn) were significantly influenced by diet treatment whereas this was not true for the other minerals investigated, i.e. chromium (Cr), copper (Cu) , iron (Fe), potassium (K), Mg, manganese (Mn) and sodium (Na) (Table 4). The Neumann-Keuls multiple range test with PI 0.05was not able to detect significant differences among groups for whole body levels of Ca and P, although there was a trend for Ca and P to be inversely related to the dietary levels of UDC and UDSC. Body levels of Zn were significantly depressed in fish fed diet UDSC-H. Fish fed diets with DP displayed normal mineral levels. Thyroid follicle epithelial cell heights in trout on day 85 were directly related to the dietary level of each of the three test RPC sources and to the dietary glucosinolate levels originating from these sources. Values for TFECH were lowest in fish fed diets containing DP whereas they were elevated significantly in fish fed diets UDC-H and UDSC-H (Fig. 5). The latter finding did not bear any direct relationship to the dietary glucosinolate levels. Estimated dietary glucosinolate levels, for example, ranged from 156-467 pmollkg dry diet (UDC diets), 65-196 (DP diets) and 48-144 (UDSC diets).
4. Discussion Our findings suggest that undephytinized and dephytinized RPC may comprise about 39% of the dietary protein for rainbow trout without adversely affecting growth rate, feed intake, feed and protein utilization, health and survival. Indeed, the use of the foregoing specially processed rapeseed (or canola) protein sources would permit a dramatic reduction in the level of fish meal usage in juvenile rainbow trout diets under our conditions (fish meal was successfully reduced to only 11% of diet). It is unknown whether the findings of the present study can be extrapolated to other salmonid species. However, this is likely since trout appear to be more sensitive than salmon (e.g. juvenile chinook salmon) to constituents within canola meal, such as glucosinolates and phenolic compounds which adversely affect growth, feed intake and other aspects of performance (Higgs et al., 1983; Hilton and Slinger, 1986). It is noteworthy that the growth rates of trout in this study were below those reported by Austreng et al. ( 1987) for the Sunndalsora strain of rainbow trout, assuming similar starting
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weights, water temperatures, and satiation feeding. This perhaps raises some doubts about the validity of the afore-mentioned findings. The Spring Valley trout of this study, unlike the Sunndalsora strain, however, have not undergone intensive genetical selection. Moreover, the overall growth responses of the trout fed diets HM, UDC-L, UDC-M, DP-L, DPM, UDSC-L and UDSC-M were similar to the range expected for Ontario trout, assuming identical conditions and experimental duration (Cho, 1992). Ontario trout have also not been subjected to intensive genetical selection. Austreng et al. ( 1987) also suggested that trout held under conditions and within the size range of those in the present study should have a feed efficiency of close to 1.0. Trout fed diet HM had a FE value of 0.61. This suggests that there was significant feed wastage and/or less than optimal diet digestibility. Feed wastage, however, was noted to be negligible. Diet digestibility was not assessed, but the findings of Hajen et al. ( 1993) for chinook salmon in seawater showed that three of the dietary components used in this study, namely wheat middlings, and British Columbia sources of poultry-by-product meal and blood meal, had poor digestibility in salmon. Hence, the lower than anticipated values for FE of trout in this study were probably a consequence of reduced diet digestibility rather than overfeeding. Lastly, our results both confirm and extend those of McCurdy and March ( 1992). The latter researchers found that solvent-washed, fiber-reduced canola meal (upgraded canola meal) could comprise 40% of the dietary protein of trout and 25% of the dietary protein of salmon without adversely affecting growth and feed utilization. It is noteworthy that the study on trout was of short duration (3 weeks). Also, there was no attempt to progressively replace herring meal in the basal diet. Indeed, the diet with upgraded canola meal also contained 21.5% herring meal of unspecified quality. Nevertheless, the results of both studies agree with respect to the acceptable dietary level of these specially processed rapeseedlcanola protein products for trout. The success of both studies can likely be attributed to the reduced levels of glucosinolates, phenolic compounds and carbohydrates (indigestible and digestible) in the test protein sources. Glucosinolates are known to account for much of the poor acceptability of canola meal in trout ( < 13.3-18% of dietary protein) and juvenile Pacific salmon (13-22% of dietary protein) diets (Higgs et al., 1983, 1995a; Fagerlund et al., 1987; Leatherland et al., 1987), Also, tannins may depress protein and dry matter digestibility (Krogdahl, 1989), and sinapine may adversely affect the palatability of rapeseed/canola meals (McCurdy and March, 1992). Extraction of most of the afore-mentioned compounds during the preparation of rapeseedlcanola protein concentrates (Jones, 1979) and upgraded canola meals (McCurdy and March, 1992) would be expected to improve their nutritive value considerably. It is also noteworthy that the FRI-73 process that was employed to produce the Bronowski RPC used in this study decreased the levels of carbohydrates such as raffinose and stachyose. This would also be expected to enhance the nutritive value of RPC for salmonids (Arnesen et al., 1989). Pretreatment of RPC with Finase S 2X to reduce phytic acid content (Table 1) did not markedly improve its nutritive value for trout. This finding probably occurred because the procedure used to dephytinize RPC significantly reduced the quality of the RPC protein. Consequently, the benefits of phytate removal on the nutritive value of RPC were less than anticipated (compare performance of fish fed diets UDC-H, DP-H and UDSC-H) .
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It is noteworthy that mineral levels were normal in trout receiving diets containing dephytinized RPC, whereas some reduction in zinc bioavailability was observed in fish consuming the diets with undephytinized RPC (especially in fish fed diet UDSC-H) . Also, thyroid function, as judged by histological criteria, was not significantly different between fish receiving the HM diet and those ingesting the diets with dephytinized RPC. By contrast, trout consuming the diets containing undephytinized RPC had increased thyroid activity, possibly to counteract some impairment of thyroid hormone synthesis and perhaps of conversion of thyroxine to 3,5,3’-triiodo-L-thyronine by glucosinolate hydrolytic products (Higgs et al., 1995a) and/or in response to increased protein intake (Eales et al., 1992). The latter assumes that phytic acid present in native form in RPC exerts a negligible influence on protein availability in salmonids. This assumption appears to be valid (protein digestibility coefficients for RPC in trout and salmon range from 89.0-98%; Higgs et al., 1994, 1995a). Previously, Yurkowski et al. ( 1978) demonstrated that feed intake in rainbow trout was depressed when RPC was substituted totally for fish meal in the diet even though RPC contains reduced levels of phenolic constituents. In the present study, suppression of feed intake was not found when fish meal was replaced completely by each of the RPC sources. Apparently, the addition of 1.5% FinnstimTM to all diets was efficacious in maintaining trout feed intake, regardless of diet treatment. However, this conclusion requires confirmation since diets containing RPC were not tested with and without FinnstimTM. In general, none of the diet treatments affected whole body proximate composition. This suggests that the differences between groups in size, level of feed (available energy) intake, and proportions of total available dietary energy originating from protein and lipid were not of sufficient magnitude to affect body compositions. All of the preceding variables are known to influence the extent of triacylglycerol deposition in salmonids (Higgs et al., 1995b). In conclusion, complete replacement of HM protein in rainbow trout diets by RPC may be possible if the methodology for phytate removal is improved. Also, the available levels and balance of essential amino acids in RPC-based diets may require optimization.
Acknowledgements We gratefully acknowledge the help and financial assistance provided by Alko Ltd. of Finland and the Western Regional Aquaculture Consortium (U.S. funded).
References Arnesen, P., Brat&, L.E., Olli, J. and Krogdahl, A., 1989. Soybean carbohydrates appear to restrict the utilization of nutrients by Atlantic salmon (S&IO s&r L.). In: M. Takeda and T. Watanabe (Editors), Proceedings of the Third International Symposium on Feeding and Nutrition in Fish. Laboratory of Fish Nutrition, Tokyo University of Fisheries, Tokyo, Japan, pp. 273-280. Austreng, E., Storebakken, T. and Asgard, T., 1987. Growth rate estimates for cultured Atlantic salmon and rainbow trout. Aquaculture, 60: 157-160. Barlow, S., 1989. Fishmeal - world outlook to the year 2,000. Fish Farmer, 12: 12-15.
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Beamish, F.W.H., Hilton, J.W., Niimi, E. and Slinger, S.J., 1986. Dietary carbohydrate and growth, body composition and heat increment in rainbow trout (Sulmo gairdneri), Fish Physiol. Biochem., 1: 85-9 1. Bell, J.M., 1993. Factors affecting the nutritional value of canola meal: a review. Can. J. Anim. Sci., 73: 6794597. Cheryan, M., 1980. Phytic acid interactions in food systems. CRC Crit. Rev. Food Sci. Nutr., 13: 297-335. Cho, C.Y., 1990. Fish nutrition, feeds, and feeding: with special emphasis on salmonid aquaculture. Food Rev. lnt., 6: 333-357. Cho, C.Y., 1992. Feeding systems for rainbow trout and other salmonids with reference to current estimates of energy and protein requirements. Aquaculture, 100: 107-123. Clancy, G.S., 1992. Effect of spoilage and processing conditions on the nutritive value of various marine protein sources for rainbow trout (Oncorhynchus mykiss) and chinook salmon (Oncorhynchus rshawytscha), MSc. Thesis, University of British Columbia, Vancouver, B.C., 215 pp. Clarke, W.C., Virtanen, E., Blackbum, J. and Higgs, D.A., 1994. Effects of dietary betaine/amino acid additive on growth and seawater adaptation in yearling chinook salmon. Aquaculture, 121: 137-145. EaIes, J.G., MacLatchy, D.L., Higgs, D.A. and Dosanjh, B.S., 1992. The influence of dietary protein and caloric content on thyroid function and hepatic thyroxine 5’-monodeiodinase activity in rainbow trout, Oncorhynchus mykiss. Can. J. Zool., 70: 1526-1535. Erdman, J.W. Jr., 1979. Oilseed phytates: nutritional implications. J. Am. Oil. Chem. Sot., 56: 736-741. Fagerlund, U.H.M., Higgs, D.A., McBride, J.R., Archdekin, C., Dosanjh, B.S. and Eales, J.G., 1987. Nutritional value of canola meal protein for juvenile coho salmon (Oncorhynchus kisutch). 8th Prog. Rep., Research on canola seed, oil, meal and meal fractions, Canola Council of Canada, Winnipeg, MB., pp. 5-13. Hajen, W.E., Higgs, D.A., Beames, R.M. and Dosanjh, B.S., 1993. Digestibility of various feedstuffs by postjuvenile chinook salmon (Oncorhynchus tshawytscha) in sea water. 2. Measurement of digestibility. Aquaculture, 112: 333-348. Higgs, D.A., 1986. Feeding fish efficiently. Can. Aquacult. Mag., 2(2): 15, 17, 18.26. Higgs, D.A., Marketi, J.R., MacQuanie, D.W., McBride, J.R., Dosanjh, B.S., Nichols, C. and Hoskins, G., 1979. Development of practical diets for coho salmon, Oncorhynchus kisurch, using poultry-by-product meal, feather meal, soybean meal and rapeseed meal as major protein sources. In: J.E. Halver and K. Tiews (Editors), Finfish Nutrition and Fishfeed Technology, Vol. 2, Heenemann Verlagsgesellschaft mbH, Berlin, pp. 191218. Higgs, D.A., McBride, J.R., Markert, J.R., Dosanjh, B.S., Plotnikoff, M.D. and Clark, W.C., 1982. Evaluation of Tower and Candle rapeseed (canola) meal and Bronowski rapeseed protein concentrate as protein supplements in practical dry diets for juvenile chinook salmon (Oncorhynchus tshawytscha). Aquaculture, 29: I-31. Higgs, D.A., Fagerlund, U.H.M., McBride, J.R., Plotnikoff, M.D., Dosanjh, B.S., Markert, J.R. and Davidson, J., 1983. Protein quality of Altex canola meal for juvenile chinook salmon (Oncorhynchus tshawytscha) considering dietary protein and 3,5,3’-triiodo-L-thyronine content. Aquaculture, 34: 213-238. Higgs, D.A., McBride, J.R., Dosanjh, B.S., Clarke, W.C., Archdekin, C. and Hammons, A.-M., 1988. Nutritive value of plant protein sources for fish with special emphasis on canola products. In: Proceedings, Aquaculture International Congress, British Columbia Pavilion Corp., Vancouver, B.C., pp. 417435. Higgs, D.A., McBride, J.R., Dosanjh, B.S. and Fagerlund, U.H.M., 1990. Potential for using canola meal and oil in fish diets. In: R.C. Ryans (Editor), Fish Physiology, Fish Toxicology, and Fisheries Management. Proceedings of an International Symposium, Guangzhou, PRC, September 14-16, 1988, pp. 88-107. Higgs, D.A., Prendergast, A.F., Dosanjh, B.S., Beames, D.M., Deacon, G. and Hardy, R.W., 1994. Canola protein offers hope for efficient salmon production. In: D.D. Mackinlay (Editor), High Performance Fish, Fish Physiology Assoc., Vancouver, Canada, pp. 377-382. Higgs, D.A., Dosanjh, B.S., Prendergast, A.F., Beames, R.M., Hardy, R.W., Riley, W. and Deacon, G., 1995a. Use of rapeseed/canola protein products in finfish diets. In: D. Sessaand C. Lim (Editors), AOCS monograph, Nutrition and Utilization Technology in Aquaculture. AOCS Press, Champaign, FL, pp. 130-156. Higgs, D.A., Macdonald, J.S., Levings, C.D. and Dosanjh, B.S., 1995b. Nutrition and feeding habits of Pacific salmon (Oncorhynchus species) in relation to life history stage. In: C. Groot, L. Margolis and W.C. Clarke (Editors), Physiological Ecology of Pacific Salmon, UBC Press, Vancouver, B.C., in press. Hilton, J.W. and Slinger, S.J., 1981. Nutrition and feeding of rainbow trout. Can. Spec. Publ. Fish. Aquat. Sci., No. 55: 15 pp. Hilton, J.W. and Slinger, S.J., 1986. Digestibility and utilization of canola meal in practical-type diets for rainbow trout (Salmo gairdneri). Can. J. Fish. Aquat. Sci., 43: 1149-l 155.
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Jones, J.D., 1979. Rapeseed protein concentrate preparation and evaluation. .I. Am. Oil Chem. Sot., 56: 716-721. Krogdahl, A., 1989. Alternative protein sources from plants contain antinutrients affecting digestion in salmonids. In: M. Takeda and T. Watanabe (Editors), Proceedings of the Third International Symposium on Feeding and Nutrition in Fish. Laboratory of Fish Nutrition, Tokyo University of Fisheries, Tokyo, Japan, pp. 253-261. Lall, S.P., 1989. The minerals. In: J.E. Halver (Editor), Fish Nutrition, 2ndedn. Academic Press, New York, NY, pp. 219-257. Leatherland, J.F., Hilton, J.W. and Slinger, S.J., 1987. Effects of thyroid hormone supplementation of canola meal-based diets on growth, and interrenal and thyroid gland physiology of rainbow trout (Salmo gairdneri) Fish Physiol. Biochem., 3: 73-82. Mackie, A.M. and Mitchell, AI., 1985. Identification of gustatory feeding stimulants for fish-applications in aquaculture. In: C.B. Cowey, A.M. Mackie and J.G. Bell (Editors), Nutrition and Feeding in Fish. Academic Press, Toronto, pp. 177-189. McBride, J.R. and Van Overbeeke, A.P., 1971. Effects of androgens, estrogens, and cortisol on the skin, stomach, liver, pancreas and kidney in gonadectomized adult sockeye salmon (Oncorhynchus net&z). J. Fish Res. Board Can., 28: 485490. McCallum, I.M. and Higgs, D.A., 1989. An assessment of processing effects on the nutritive value of marine protein sources for juvenile chinook salmon (Oncorhynchus ehawytscha). Aquaculture, 77: 181-200. McCurdy, S.M. and March, B.E., 1992. Processing of canola meal for incorporation in trout and salmon diets, J. Am. Oil Chem. Sot., 69: 213-220. NRC (National Research Council), 1983. Nutrient Requirements of Warmwater Fishes and Shellfishes. National Academy Press, Washington, DC, 112 pp. Ogino, C., 1980. Requirements of carp and rainbow trout for essential amino acids. Bull. Jpn. Sot. Sci. Fish., 46: 171-174. Oser, B.L., 1959. An integrated essential amino acid index for predicting the biological value of proteins. In: A.A. Albanese, (Editor), Protein and Amino Acid Nutrition. Academic Press, New York, NY, pp. 281-295. Pike, I.H., Andorsdottir, G. and Mundheim, H., 1990. The role of fish meal in diets for salmonids. International Association of Fish Meal Manufacturers. No. 24: 35 pp. Richardson, N.L., Higgs, D.A., Beames, R.M. and McBride, J.R., 1985. Influence of dietary calcium, phosphorus, zinc and sodium phytate level on cataract incidence, growth and histopathology in juvenile chinook (Oncorhynchus tshawytscha). J. Nutr., 115: 553-567. Rumsey, G.L., 1993. Fish meal and alternate sources of protein in fish feeds update 1993. Fisheries, 18: 14-19. Sandberg, A.-S., Andersson, H., Carlsson, N.-G. and Sandstrom, B., 1987. Degradation products of bran phytate formed during digestion in the human small intestine: effect of extrusion cooking on digestibility. J. Nutr., 117: 2061-2065. Spinelli, J., Houle, C.R. and Wekell, J.C., 1983. The effect of phytates on the growth of rainbow trout (S&to gairdneri) fed purified diets containing varying quantities of calcium and magnesium. Aquaculture, 30: 7 l83. Tholen, J.T., Shifeng, S. and Thruscott, R.J.W., 1989. The thymol method for glucosinolate determination. J. Sci. Food Agric., 49: 157-165. Van Overbeeke, A.P. and McBride, J.R., 1971. Histological effects of 1 I-ketotestosterone, 17a-methyltestosterone, estradiol, estradiol cypionate, and cortisol on the interrenal tissue, thyroid gland, and pituitary gland of gonadectomized sockeye salmon (Oncorhynchus nerka) J. Fish Res. Board Can., 28: 477-484. Yurkowski, M., Bailey, J.K., Evans, R.E., Tabachek, J.A.L., Ayles, G.B. and Eales, J.G., 1978. Acceptability of rapeseed proteins in diets of rainbow trout (S&to gairdneri). J. Fish. Res. Board Can., 35: 951-962.
Assessment of undephytinized and dephytinized rapeseed protein concentrate as sources of dietary protein for juvenile rainbow trout (Oncorhynchus
mykiss)
Z. TeskeredZC”, D.A. Higgsb,*, B.S. Dosanjhb, J.R. McBrideb, R.W. Hardy”, R.M. Beamesd, J.D. Jones’, M. Sirnell”, T. Vaarae, R.B. Bridges” aThe Institute
ofRuder Boskovic, Centre forMarine Research, Zagreb Laboratory for Aquaculture,
Bijenicka 54, 4100 Zagreb, Croatia “Fisheries and Oceans Canada, West Vancouver Laboratory, 4160 Marine Drive, West Vancouver, B.C., V7V IN6 Canada “Northwest Fisheries Science Center, 2725 Montlake Boulevard East, Seattle, WA 98112, USA ‘Department of Animal Science, University ofBritish Columbia, 248 2357 Main Mall, MacMillan Building, Vancouver, B.C., V6T 2A2 Canada ‘Alko Ltd., Process and Product Development, SF 05200, Rajamiiki, Finland
Accepted 3 October 1994
Abstract This study was undertaken to evaluate three sources of rapeseed protein concentrate (RPC) as partial or total replacements of steam-dried whole herring meal (HM) in a practical diet for juvenile rainbow trout. Groups of 4.2-4.4 g trout held in lO.O-10.3”C well water on a natural photoperiod were fed one of 10 isonitrogenous (43% protein) and isoenergetic (21.6 MJ gross energy/kg) diets to satiation 3 times daily. Each of three test protein sources, viz. undephytinized, untreated control RPC (UDC) , undephytinized solvent-treated control RPC (UDSC) , and dephytinized RPC (DP), comprised about 19.0, 39.0 and 59.0% respectively of dietary protein by replacement of one-third (L), two-thirds (M) and all (H) of the HM protein in the control diet. Rainbow trout growth rate, feed intake, feed efficiency, protein and gross energy utilization, mortality and health were not compromised when either UDC or DP replaced up to 66% of HM protein in the control diet. Total replacement of HM protein with each of the RPC sources did not depress feed intake, but did significantly reduce growth rate, feed efficiency, and protein and energy utilization. The procedure *Corresponding author. ‘This paper is dedicated to the memory of Dr. John D. Jones, formerly of the Food Research Centre, Central Experimental
Farm, Ottawa, ON KlA OC6, Canada.
0044~8486/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDIOO44-8486(94)00334-3
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used to dephytinize RPC lowered RPC protein quality. Whole body concentrations of calcium and phosphorus were inversely related to the dietary levels of UDC and UDSC. Body levels of zinc were significantly depressed in fish fed the diet with UDSC-H. Fish fed diets with DP displayed normal mineral levels. Significant elevation of thyroid follicle epithelial cell heights was found only in those groups fed the diets with UDC-H or UDSC-H. Whole body proximate composition was generally uninfluenced by diet treatment. It is concluded that RPC can comprise 39% of the dietary protein (fish meal only I 1%) for rainbow trout without adversely affecting performance. Nutritional strategies that may enable complete replacement of fish meal protein in diets for rainbow trout by RPC are outlined. Keywords: Rapeseed protein concentrate; Oncorh.ynchus mykiss; Feeding and nutrition-fish,
dietary value
1. Introduction Feed accounts for 40-60% of the operating costs of salmon farms, with almost two-thirds of the feed cost originating from the protein sources (Higgs, 1986; Higgs et al., 1995a). High-quality fish meals are used extensively ( > 50% of diet) in formulated salmon diets to meet the high dietary protein requirements of farmed salmon in seawater (Higgs et al., 1995b). This practice largely accounts for the high cost of the protein moiety of salmon feeds. Fish meals, however, can vary markedly in quality and price (McCallum and Higgs, 1989; Pike et al., 1990; Clancy, 1992). In addition, future supplies of fish meal will probably be lower and prices higher than at present (Barlow, 1989; Rumsey, 1993; Higgs et al., 1994a). Consequently, future fish farming production costs will probably increase unless suitable inexpensive alternative protein sources that are of consistently high quality are identified and/or developed. Canola is the name given to genetically selected varieties of rapeseed of the Brussica naps and B. campestris species that are low in both glucosinolates or antithyroid factors ( < 30 pmol of alkenyl glucosinolates per gram of oil-free dry matter of seed) and erucic acid ( < 2% of total fatty acids in the oil) (Bell, 1993). The amount of rapeseed/canola protein potentially available for inclusion in animal diets exceeds the annual global production of fish meal protein (Higgs et al., 1995a). Further, the cost of canola meal expressed in US $/kg protein is presently 63.5% of that of Chilean anchovy meal (0.47 versus 0.74 $/kg protein) (Higgs et al., 1994). The quality of rapeseed/canola protein has also been judged by Higgs et al. (1988, 1990) to be equivalent to that of whole herring meal and higher than that of soybean meal and cottonseed meal using the essential amino acid index approach of Oser ( 1959). Complete realization of the high quality of rapeseed/canola protein is compromised by the presence of antinutritional factors. Some of these are common to all oilseed protein products, e.g. fiber, carbohydrates, phenolic compounds and phytic acid. Others are unique, e.g. glucosinolates (Higgs et al., 1995a). Rapeseed/canola protein concentrates, relative to canola meal, contain reduced levels of glucosinolates, fiber, nitrogen-free extract, and phenolic constituents, e.g. sinapine and tannins. Also, they have significantly higher levels of digestible protein and energy for salmonids (Hajen et al., 1993; Higgs et al., 1994, 1995a). By contrast, the concentrates have higher levels of phytic acid (5.3-7.5%; Erdman,
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263
1979; Jones, 1979) than the meals (3.1-3.7%; Cheryan, 1980; McCurdy and March, 1992). Phytic acid, the hexaphosphate of myoinositol, is strongly negatively charged at all pH values normally encountered in feed. This compound has strong affinity for proteins at low pH and for cations such as zinc at intestinal pH’s. High dietary levels of phytic acid may depress growth, feed efficiency, bioavailability of protein and zinc as well as thyroid function in salmonids (Spinelli et al., 1983; Richardson et al., 1985). Previous research with juvenile rainbow trout (Yurkowski et al., 1978) and chinook salmon (Higgs et al., 1982) showed that rapeseed protein concentrate (RPC) may comprise more than 24% of the dietary protein by replacement of fish meal. Neither of these studies, however, established the upper limits of RPC that could be substituted for fish meal without compromising fish performance. Also, no attempt was made in these studies to assess whether the nutritive value of RPC could be improved by dephytinization (removal of its phytic acid content). In this study, we evaluated the merits of three sources of RPC (undephytinized, untreated control; undephytinized, solvent-treated control; dephytinized) as partial or total replacements of steam-dried whole herring meal in a practical diet for rainbow trout.
2. Materials and methods Fish and experimental conditions In January, 1990, Spring Valley rainbow trout (Oncorhynchus rnykiss) were selected for uniform size (mean weight + 1 s.d.). Then they were distributed randomly into 20 800liter fibreglass tanks so that each contained 74-77 trout (range in initial mean weight, 4.24.4 g). All groups were held in flowing (7.5 l/min), [email protected]”C well water on a natural photoperiod for the duration of the study (84 days). Dissolved oxygen content of the water during the experiment ranged from 9.9-10.6 mg/l. Diets and feeding protocol Ten dry diets (control diet based upon University of Guelph trout formulations, Hilton and Slinger, 1981) of equivalent protein, lipid and gross energy content (43%, 18% and 21.6 MJ/kg on a dry weight basis, respectively) were prepared according to Higgs et al. (1979). The diets were distinguished on the basis of the control and test protein sources employed (i.e. steam-dried whole herring meal HM; undephytinized untreated control RPC, UDC; undephytinized, solvent-treated control RPC, UDSC; and dephytinized RPC, DP) and according to the level of replacement of HM protein in the control diet (i.e. one-third, L; two-thirds, M; and total, H replacement). Thus, DP-M signifies that dephytinized RPC replaced 66% of the HM protein in the control diet. Each of the three test sources of RPC (Bronowski FRI-73-5 (343) ) comprised about 19.0, 39.0 and 59% of the dietary protein as the HM protein in the control diet was removed progressively (Table 1). UDSC was included in the experiment to determine whether the incubation and drying conditions that were used during the dephytinization process influenced the quality of the RPC protein (negative control). The dietary mineral levels were generally equalized in each case (Table 2) by preparing separate mineral supplements following analysis of each protein source for mineral content by plasma emission spectroscopy (Higgs et al., 1982). All diets were
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Table 1 Ingredient composition and protein, lipid and energy contents of test diets fed to juvenile rainbow trout for 84 days Ingredient
Herring meal Rapeseed protein concentrate Undephytinized Dephytinized Undephytinized, solvent control Wheat middlings Herring oil (stabilized)’ Lx.-Methionine L-Lysine Santoquin CaHPO, CaCO, Constant components” Protein (%) Lipid (%) Gross energy (MJ/kg)’ Metabolizable energy’
Diet (g/kg dry weight)” HM”
UDC-L UDC-M UDC-H DP-L
DP-M
DP-H
320
213.3
106.7
-
213.3
106.7
-
213.3
106.7
_ _
121.1 _
242.2 _
363.3 _
130.1
260.2
-
-
_
~390.3
_ _ _ _ 169.5 140.0 189.6 152.7 115.5 123.2 127.0 118.8 121.1 123.4 3.99 4.00 3.40 3.94 3.84 _ _ 1.40 1.30 0.012 0.037 0.062 0.086 0.037 0.063 0.088 _ 12.4 15.9 18.3 12.8 17.4 20.5 _ _ 6.6 13.9 6.0 13.1 33 1.9 331.9 331.9 331.9 331.9 331.9 331.9 45.1 43.3 41.9 42.3 45.3 42.0 43.1 17.8 17.8 18.1 18.6 17.7 18.0 18.1 22.2 21.7 21.4 21.7 22.0 21.3 21.5 17.1 16.7 16.6 16.8 17.0 16.5 16.7 _
228.04 116.5 3.54
197.7 120.0 3.58 _
UDSC-L UDSC-M UDSC-H
126.5 193.4 118.7 3.40 0.037 12.7 331.9 43.0 17.7 21.5 16.6
253.0 160.6 120.9 3.88 _ 0.063 16.3 6.7 331.9 42.2 18.0 21.4 16.6
379.5 127.2 123.1 3.88 1.38 0.088 18.9 14.2 331.9 43.6 17.8 21.6 16.7
6.8 0.8
12.0 1.6
19.0 2.5
(MJk) Inositol phosphate (IPY (wmol/g) IP6 IP5
1.8 0
6.5 0
13.0 0
18.0 1.7
2.0 0
2.2 0.4
1.8 0
The diets have been distinguished on the basis of the control and test protein sources employed and the level of herring meal replaced in the control (HM) diet. “Steam-dried whole herring meal stabilized with 250 mg ethoxyquin/kg. hHM = herring meal; UDC = undephytinized, untreated control RPC; DP = dephytinized RPC; UDSC = undephytinized, solvent-treated control RPC. The letters L, M and H refer respectively to 4, 3 and complete replacement of herring meal protein with the test protein source. ‘Stabilized with 0.5 g santoquin/kg oil. “Common dietary components (g/kg dry diet) were as follows: poultry by-product meal, 70; blood meal, 40; corn gluten meal, 65; dried whey, 60; vitamin/mineral supplement, 50; choline chloride (60%), 5; ascorbic acid, 2; permapell, 9.92; FinnstimTM715.7de&in, 15. The vitamin supplement supplied the following levels of nutrients/kg dry diet: vitamin A acetate, 5000 IU; cholecalciferol ( Dz), 2400 IU; m-ol-tocopheryl acetate (E), 300 IU; menadione, 18 mg; o-calcium pantothenate, 192.5 mg; pyridoxine HCI, 49.3 mg; riboflavin, 60 mg; niacin, 300 mg; folic acid, 15 mg; thiamine mononitrate, 56 mg; biotin, 1.5 mg; cyanocobalamin (B ,*), 0.09 mg; inositol, 400 mg. Refer to Table 2 for the composition of the mineral supplements. ‘Estimated by ascribing 0.0236 MJ/g protein, 0.0395 MJ/g lipid and 0.0172 M.J/g carbohydrate (Higgs et al., 1995b). ‘Estimated by ascribing0.0188 MJ/g protein, 0.0356 MJ/g lipid, 0.0159 MJ/g animal carbohydrate, 0.0134 MJ/g dextrin and 0.00669 MJ/g raw starch (Higgs et al., 1983; Beamish et al., 1986). xIP4 and IP3 were not detected.
3322 5 4.5 2.8 0.2 5
_
2632 763 1007 6.5 46 109 75 995 566
HM
DieP
1365 1365 1365 5 4.5 2.7 0.2 5
1082 1082 1478 5 4.5 2.8 0.2 5 1056 1056 1671 5 4.5 2.8 0.2 5
482 6.4 72 107 64 2052 _
2911 1324 _
_
3768
DP-L
1412 1412 1412 5 4.5 2.9 0.2 5
275 6.3 98 104 52 2543
5114 2418 3950 1119
DP-M
and > 0.06% magnesium
1502 1502 1502 5 4.5 2.7 0.2 5
442 6.8 119 102 38 3522
5403 5573 4174 1190
UDC-H
phosphorus
275 6.6 94 104 50 2868 _
4675 2639 3613 1081 _
UDC-M
1108 1108 1520 5 4.5 2.8 0.2 5
408 6.3 74 107 64 2228
2893 1204
3744 _
UDSC-L
1383 1383 1383 5 4.5 2.7 0.2 5
215 6.2 101 105 52 2896 _
4790 2695 3702 1096 _
UDSC-M
1521 1521 1521 5 4.5 2.7 0.2 5
442 6.0 130 103 41 3563
5559 5669 4294 1205
UDSC-H
from animal sources and the mineral supplement.
1565 1565 1565 5 4.5 2.9 0.2 5
442 6.2 124 102 41 3034
6039 5260 4666 1240 _
DP-H
in the test diets, expected levels of dietary minerals and means of the dietary concentrations
350 6.5 67 106 62 2214
2818 1171 _
3648
UDC-L
employed
“Refer to Table 1 for diet designations. “All diets were formulated to have 2 0.7% inorganic ‘Not determined.
K (as KzSW (as WW (as KH,PO,) I (as KIOa) F(asNaF) Co (as CoC1,.6H,O) Se (as Na,SeOl) Al (as AlC13.6H20)
Ca (as CaHPO,) (as CaCO,) P (as CaHPO,) (as KH,P04) ( as N&PO,. H,O) Mg (as MgSO,.7H,O) Cu (as CuS04.5Hz0) Fe (as FeS04.7H,0) Zn (as ZnSO,.7H,O) Mn (as MnSO,.H,O) Na (as NaCl) (asNaH,PO, . H,O)
Mineral
Table 2 Composition of mineral supplements (mg/kg dry diet)
15 24.5 3 to.2 >5
8024
200tX3315b 15 335 150 90 4600
13675h
15495
Expected total
as determined
ND
ND” 20.2
25 24.5
7331
25684332 19 364 237 100 5642
15634
17442
Determined level
by analysis
266
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formulated to have 2 0.7% inorganic phosphorus (P) and 2 0.06% magnesium (Mg) from animal and inorganic sources (Lall, 1989). The mean dietary concentrations of minerals as determined by plasma spectroscopy are provided in Table 2. Since Yurkowski et al. ( 1978) had previously noted significant depression of feed intake in trout when fish meal was replaced totally by RPC in the absence of diet palatability enhancers, all diets were supplemented with 1.5% FinnstimTM. FinnstimTM contains 94% betaine (anhydrous) in combination with 3% of an L-amino acid mixture that is mainly alanine, serine, isoleucine, leucine, valine and glycine (Clarke et al., 1994). Betaine and L-amino acids are thought to act as diet palatability enhancers (Mackie and Mitchell, 1985), and it was hoped that the FinnstimTM would counteract any suppression of feed intake that might occur in trout fed diets in which fish meal was partially or totally replaced by RPC. On the basis of published values for the amino acid compositions of protein sources other than RPC (NRC, 1983) and analyzed values for UDC and DP ( AAA Laboratory, Mercer Island, WA, USA), it was estimated that the diets met or exceeded the known indispensable amino acid needs of rainbow trout as provided by Ogino ( 1980)) Cho ( 1990)) and Higgs et al. ( 1995b). All groups were fed their assigned diet by hand 3 times daily until the point of satiety. Feed wastage was negligible at each feeding time (08.00-09.30, 11 .OO-12.00, and 15.0016.00 h). Diet pellet size was based upon the recommendations of Hilton and Slinger ( 198 1) . The daily feed intake and mortality of each group were recorded. Fish weighing, sampling and chemical and histological analyses All fish were removed from their respective tanks every 21 days following a minimum of 17 h of food deprivation. Sixty fish, selected at random from each group, were anaesthetized (2 phenoxyethanol, 0.33 ml/l) and individually weighed (nearest 0.01 g) and measured (fork length, nearest 0.1 cm). The fish were fed to satiation once on each weighing day between 15.00 and 16.00 h. Four samples of 9 fish were analyzed for initial whole body proximate and mineral compositions. Ten fish were removed randomly from each replicate (tank) on day 84 for determination of final whole body proximate and mineral compositions (5 pools of 2 fish each per replicate). Three fish were sampled from each replicate on day 85 for histological examination of the liver, kidney, thyroid and alimentary tract. Whole body and diet proximate compositions were determined according to the procedures outlined by Higgs et al. ( 1979). Carcass mineral compositions were determined using plasma emission spectroscopy (Higgs et al., 1982). Total levels of glucosinolates in UDC, DP and UDSC were assayed according to the thymol procedure of Tholen et al. ( 1989). Dietary glucosinolate contents were calculated and expressed as pmollkg dry diet. Dietary levels of inositol phosphates were determined using the procedures of Sandberg et al. ( 1987). Histological examinations of the selected tissues mentioned above were conducted according to the methods of McBride and Van Overbeeke ( 197 1) and Van Overbeeke and McBride ( 197 1) . RPC dephytinization Dephytinization of RPC was conducted by Alko Ltd. (Rajarnaki, Finland) according to the following protocol. Ten kg of RPC were suspended in 100 liters of water. The pH was adjusted to 5.0 and then Finase S 2X was added at a dosage of 5000 phytase units (PU) /g
2. TeskerediiCet al. /Aquaculture 131 (I995) 261-277
261
RPC ( 1 PU = amount of enzyme that liberates 1 nmol of inorganic phosphate from sodium phytate in 1 min under standard conditions of pH 5.0 and temperature of 37°C). The suspension was incubated at 55°C for 4 h, cooled and lyophilized. Control RPC (UDSC) was treated similarly, but Finase S 2X was not added. Data
calculation
and analysis
With respect to calculation of specific growth rates (SGR;% wet weight/day), the fish wet weights at each sample time were transformed to log,. Thereafter, they were subjected to a hierarchical analysis of covariance with replicates (random) nested in diets, time as the covariate and different covariate slopes allowed for each diet. Subsequently, SGR were derived from the covariate slopes as follows: SGR = ( eslope- 1) X 100. Scheffe’s test with P = 0.05 was used to detect any significant differences between the covariate slopes. Feed intake (% body weight/day) was calculated for each 21-day interval by dividing the mean daily dry feed intake per fish X 100 by the geometric mean wet weight of the fish (Richardson et al., 1985). Feed efficiency (FE) and protein efficiency ratio (PER) were calculated, respectively, as wet weight gain/dry feed or protein intake. Percent protein deposited (PPD) was calculated as protein gain X loo/protein intake. Gross energy conversion efficiency (GECE) was calculated in a similar fashion. The combustible energy values that were used for protein, lipid and carbohydrate were 0.0236 MJ/g protein, 0.0395 MJ/g lipid and 0.0172 MJ/g carbohydrate (Higgs et al., 1995b). The values for protein and lipid were used when estimating body energy content. To determine thyroid follicle epithelial cell heights (TFECH), 5 measurements were taken on each of the 5 follicles per fish. Data for feed intake, FE, PER, PPD, GECE, TFECH and levels of whole body proximate constituents and minerals were analyzed by one-way ANOVA with replicate nested in diet Table 3 Feed intake (mean daily dry feed intake per fish X 100 + geometric mean wet weight of fish) of juvenile rainbow trout during each 21-day interval of an 84-day study in relation to diet treatment Diet”
HM UDC-L UDC-M UDC-H DP-L DP-M DP-H UDSC-L UDSC-M UDSC-H “Refer to bOne-way P
Feed intake (%/day)b o-21
2142
42-63
63-84
4.38 4.48 4.31 4.20 4.14 4.28 4.44 4.04 4.44 4.34
4.1gab 3.13” 4.10ab 4.69b 4.01ab 4.02”b 4.4Y 4.01ab 4.7@ 4.71b
4.13a 3.61” 3.78” 4.60ab 3.91a 3.99” 4.28” 3.68” 4.06” 5.00b
3.67ab 3.34” 3.43” 4.54cd 3.48” 3.71ab 4.373.36” 3.87”” 5.04d
Table 1 for diet designations. ANOVA with replicate nested in diet and replicate treated as random indicated P> 0.05 (days O-21 ) , (days 21-42). P
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I31 (1995) 261-277
RATE
3
2.5
O/o
i
d.e,f
OHM
c _
UDC
-DP
mUDSC
e,f
2
/
1.5 ii Y
’ 0.5
0 Y
FEED EFFICIENCY 0.8 0.7
I
UDC
-DP
mUDSC
ad-
0.6
/
0.4
g
0.3 0.2 0.1
g
0.50
HM
L
M
H
L
M
H
L
M
H
DIET
Fig. 1. Specific growth rates (% wet weight/day) and feed efticiencies (wet weight gain/dry feed intake) of rainbow trout between day 0 and 84 in relation to diet treatment. See Table 1 for diet designations. Diet treatment significantly influenced growth rates (P < 0.0001) and feed efficiencies (P < 0.0001) . Refer to “Materials and methods” for details of statistical analyses of data.
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131 (1995) 261-277
269
RATIO
1.8 1.6
DP
m
DP
mUDSC
UDSC
1.4 1.2 9
b
b
1 / 0.8 it 9
0.6 0.4 0.2 I
0,
PERCENT PROTEIN DEPOSITED 30
r UDC
-
25
20
O/o
‘5
10
5
r-l HM
L
M
H
L
M
H
L
M
H
DIET Fig. 2. Overall protein efficiency ratios (body weight gain (g) /protein intake (g)) and percentages of dietary protein deposited [protein gainX loo/protein intake (g) I for rainbow trout in relation to diet treatment. Diet treatment significantly influenced both indices of protein utilization (P < 0.001). Refer to Table 1 and “Materials and methods” for additional information.
270
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and replicate treated as random or by two-way ANOVA with replicate nested in each test protein source by replacement level combination (HM treatment deleted). Where appropriate, Neumann-Keuls test with P = 0.05 was used to detect significant differences among treatment means.
3. Results Values for SGR, feed intake, FE, protein utilization (PER and PPD), GECE and mortality ( < 3% of initial number in each group) of trout were not compromised when either UDC or DP replaced up to 66% of the HM protein in the control diet (Table 3; Figs. 1,2 and 3). Best overall performance (growth, FE, PER, PPD, GECE) was observed for fish fed diet UDC-L. No aberrations were noted in the histological structure of the liver, kidney, thyroid and alimentary tract, irrespective of diet treatment. Feed intake was not depressed when each of the test RPC sources replaced all of the HM protein in the control diet (Table 3). Also, feed intake was generally unaffected by the test sources of RPC but was, in contrast, directly related to the level of replacement of HM
GROSS ENERGY CONVERSION EFFICIENCY 35
r I
CJHM
30
UDC
-DP
~UDSC
d d
25
HM
L
M
H
L
M
H
L
M
H
DIET Fig. 3. Overall gross energy conversion efficiencies (gross energy gain X loo/energy intake) in relation to diet treatment. Diet treatment significantly influenced energy utilization (P < 0.0001). Refer to Table 1 and “Materials and methods” for additional information.
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ASH
3 OHM
UDC
=DP
mUDSC
2.5
2
o/o
1.5
1
0.5
0
LIPID
16 OHM
UDC
-DP
mUDSC
14 b
b
%
8 6
HM
L
M
H
H
L
M
H
Fig. 4. Final whole body percentages of ash and lipid (wet weight basis) in rainbow trout in relation to diet treatment. Diet treatment significantly affected ash and lipid percentages (P < 0.01 in each case). Percentages for whole body protein and moisture were uninfluenced by diet. Refer to Table 1 and “Materials and methods” for additional information.
212 Table 4 Final concentrations
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of selected minerals in the whole bodies of rainbow trout in relation to diet treatment
Diet”
Element (mg/kg
HM UDC-L UDC-M UDC-H DP-L DP-M DP-H UDSC-L UDSC-M UDSC-H
dry weight)b
Ca
P
Zn
17505 16027 14423 13822 17725 16494 17323 17037 16661 13975
15564 14501 13480 13292 15845 14963 15460 15221 15115 13427
115” 101”” 107”b 105”b 116b 114b 122” 115b 107a” 918
‘Refer to Table 1 for diet designations. “ANOVA indicated P< 0.05 for each element. Within a column, diet groups with the same superscript letter were not significantly different (Neumann-Keuls test with P = 0.05).
THYROID FOLLICLE EPITHELIAL CELL HEIGHT 20 OHM
UDC
-DP
mUDSC
b
P m 1C
HM
L
M
H
L
M
H
L
M
H
DIET Fig. 5. Final thyroid follicle epithelial cell heights (TFECH) for rainbow trout in relation to diet treatment. Diet treatment had a significant influence on TFECH (P < 0.05). Refer to Table 1 and “Materials and methods” for additional information.
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213
protein (two-way ANOVA). Thus, trout fed diets in which all of the HM protein had been replaced by RPC, irrespective of source, exhibited the highest feed intakes, especially after day 21 (Table 3). Performance indices, other than feed intake, were significantly reduced when fish meal was totally replaced by each of the RPC sources. Also, trout fed diet UDSC-H exhibited a significantly poorer performance than those fed diets UDC-H and DP-H (Figs. 1, 2 and 3; two-way ANOVA). Diet treatment did not significantly influence whole body moisture (range in mean values 7 1.2-72.6%) and protein (range in mean values 14&15.3%). Percentages of ash, however, were significantly lower in trout consuming diet UDC-H relative to those for fish fed all other diets except diets UDC-M and UDSC-H. Also, whole body lipid was lower in fish fed diet DP-L than in those fed all other diets except HM, DP-H and UDSC-H (Fig. 4). All other differences were not significant. Final whole body concentrations of calcium (Ca) , P and zinc (Zn) were significantly influenced by diet treatment whereas this was not true for the other minerals investigated, i.e. chromium (Cr), copper (Cu) , iron (Fe), potassium (K), Mg, manganese (Mn) and sodium (Na) (Table 4). The Neumann-Keuls multiple range test with PI 0.05was not able to detect significant differences among groups for whole body levels of Ca and P, although there was a trend for Ca and P to be inversely related to the dietary levels of UDC and UDSC. Body levels of Zn were significantly depressed in fish fed diet UDSC-H. Fish fed diets with DP displayed normal mineral levels. Thyroid follicle epithelial cell heights in trout on day 85 were directly related to the dietary level of each of the three test RPC sources and to the dietary glucosinolate levels originating from these sources. Values for TFECH were lowest in fish fed diets containing DP whereas they were elevated significantly in fish fed diets UDC-H and UDSC-H (Fig. 5). The latter finding did not bear any direct relationship to the dietary glucosinolate levels. Estimated dietary glucosinolate levels, for example, ranged from 156-467 pmollkg dry diet (UDC diets), 65-196 (DP diets) and 48-144 (UDSC diets).
4. Discussion Our findings suggest that undephytinized and dephytinized RPC may comprise about 39% of the dietary protein for rainbow trout without adversely affecting growth rate, feed intake, feed and protein utilization, health and survival. Indeed, the use of the foregoing specially processed rapeseed (or canola) protein sources would permit a dramatic reduction in the level of fish meal usage in juvenile rainbow trout diets under our conditions (fish meal was successfully reduced to only 11% of diet). It is unknown whether the findings of the present study can be extrapolated to other salmonid species. However, this is likely since trout appear to be more sensitive than salmon (e.g. juvenile chinook salmon) to constituents within canola meal, such as glucosinolates and phenolic compounds which adversely affect growth, feed intake and other aspects of performance (Higgs et al., 1983; Hilton and Slinger, 1986). It is noteworthy that the growth rates of trout in this study were below those reported by Austreng et al. ( 1987) for the Sunndalsora strain of rainbow trout, assuming similar starting
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weights, water temperatures, and satiation feeding. This perhaps raises some doubts about the validity of the afore-mentioned findings. The Spring Valley trout of this study, unlike the Sunndalsora strain, however, have not undergone intensive genetical selection. Moreover, the overall growth responses of the trout fed diets HM, UDC-L, UDC-M, DP-L, DPM, UDSC-L and UDSC-M were similar to the range expected for Ontario trout, assuming identical conditions and experimental duration (Cho, 1992). Ontario trout have also not been subjected to intensive genetical selection. Austreng et al. ( 1987) also suggested that trout held under conditions and within the size range of those in the present study should have a feed efficiency of close to 1.0. Trout fed diet HM had a FE value of 0.61. This suggests that there was significant feed wastage and/or less than optimal diet digestibility. Feed wastage, however, was noted to be negligible. Diet digestibility was not assessed, but the findings of Hajen et al. ( 1993) for chinook salmon in seawater showed that three of the dietary components used in this study, namely wheat middlings, and British Columbia sources of poultry-by-product meal and blood meal, had poor digestibility in salmon. Hence, the lower than anticipated values for FE of trout in this study were probably a consequence of reduced diet digestibility rather than overfeeding. Lastly, our results both confirm and extend those of McCurdy and March ( 1992). The latter researchers found that solvent-washed, fiber-reduced canola meal (upgraded canola meal) could comprise 40% of the dietary protein of trout and 25% of the dietary protein of salmon without adversely affecting growth and feed utilization. It is noteworthy that the study on trout was of short duration (3 weeks). Also, there was no attempt to progressively replace herring meal in the basal diet. Indeed, the diet with upgraded canola meal also contained 21.5% herring meal of unspecified quality. Nevertheless, the results of both studies agree with respect to the acceptable dietary level of these specially processed rapeseedlcanola protein products for trout. The success of both studies can likely be attributed to the reduced levels of glucosinolates, phenolic compounds and carbohydrates (indigestible and digestible) in the test protein sources. Glucosinolates are known to account for much of the poor acceptability of canola meal in trout ( < 13.3-18% of dietary protein) and juvenile Pacific salmon (13-22% of dietary protein) diets (Higgs et al., 1983, 1995a; Fagerlund et al., 1987; Leatherland et al., 1987), Also, tannins may depress protein and dry matter digestibility (Krogdahl, 1989), and sinapine may adversely affect the palatability of rapeseed/canola meals (McCurdy and March, 1992). Extraction of most of the afore-mentioned compounds during the preparation of rapeseedlcanola protein concentrates (Jones, 1979) and upgraded canola meals (McCurdy and March, 1992) would be expected to improve their nutritive value considerably. It is also noteworthy that the FRI-73 process that was employed to produce the Bronowski RPC used in this study decreased the levels of carbohydrates such as raffinose and stachyose. This would also be expected to enhance the nutritive value of RPC for salmonids (Arnesen et al., 1989). Pretreatment of RPC with Finase S 2X to reduce phytic acid content (Table 1) did not markedly improve its nutritive value for trout. This finding probably occurred because the procedure used to dephytinize RPC significantly reduced the quality of the RPC protein. Consequently, the benefits of phytate removal on the nutritive value of RPC were less than anticipated (compare performance of fish fed diets UDC-H, DP-H and UDSC-H) .
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It is noteworthy that mineral levels were normal in trout receiving diets containing dephytinized RPC, whereas some reduction in zinc bioavailability was observed in fish consuming the diets with undephytinized RPC (especially in fish fed diet UDSC-H) . Also, thyroid function, as judged by histological criteria, was not significantly different between fish receiving the HM diet and those ingesting the diets with dephytinized RPC. By contrast, trout consuming the diets containing undephytinized RPC had increased thyroid activity, possibly to counteract some impairment of thyroid hormone synthesis and perhaps of conversion of thyroxine to 3,5,3’-triiodo-L-thyronine by glucosinolate hydrolytic products (Higgs et al., 1995a) and/or in response to increased protein intake (Eales et al., 1992). The latter assumes that phytic acid present in native form in RPC exerts a negligible influence on protein availability in salmonids. This assumption appears to be valid (protein digestibility coefficients for RPC in trout and salmon range from 89.0-98%; Higgs et al., 1994, 1995a). Previously, Yurkowski et al. ( 1978) demonstrated that feed intake in rainbow trout was depressed when RPC was substituted totally for fish meal in the diet even though RPC contains reduced levels of phenolic constituents. In the present study, suppression of feed intake was not found when fish meal was replaced completely by each of the RPC sources. Apparently, the addition of 1.5% FinnstimTM to all diets was efficacious in maintaining trout feed intake, regardless of diet treatment. However, this conclusion requires confirmation since diets containing RPC were not tested with and without FinnstimTM. In general, none of the diet treatments affected whole body proximate composition. This suggests that the differences between groups in size, level of feed (available energy) intake, and proportions of total available dietary energy originating from protein and lipid were not of sufficient magnitude to affect body compositions. All of the preceding variables are known to influence the extent of triacylglycerol deposition in salmonids (Higgs et al., 1995b). In conclusion, complete replacement of HM protein in rainbow trout diets by RPC may be possible if the methodology for phytate removal is improved. Also, the available levels and balance of essential amino acids in RPC-based diets may require optimization.
Acknowledgements We gratefully acknowledge the help and financial assistance provided by Alko Ltd. of Finland and the Western Regional Aquaculture Consortium (U.S. funded).
References Arnesen, P., Brat&, L.E., Olli, J. and Krogdahl, A., 1989. Soybean carbohydrates appear to restrict the utilization of nutrients by Atlantic salmon (S&IO s&r L.). In: M. Takeda and T. Watanabe (Editors), Proceedings of the Third International Symposium on Feeding and Nutrition in Fish. Laboratory of Fish Nutrition, Tokyo University of Fisheries, Tokyo, Japan, pp. 273-280. Austreng, E., Storebakken, T. and Asgard, T., 1987. Growth rate estimates for cultured Atlantic salmon and rainbow trout. Aquaculture, 60: 157-160. Barlow, S., 1989. Fishmeal - world outlook to the year 2,000. Fish Farmer, 12: 12-15.
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Beamish, F.W.H., Hilton, J.W., Niimi, E. and Slinger, S.J., 1986. Dietary carbohydrate and growth, body composition and heat increment in rainbow trout (Sulmo gairdneri), Fish Physiol. Biochem., 1: 85-9 1. Bell, J.M., 1993. Factors affecting the nutritional value of canola meal: a review. Can. J. Anim. Sci., 73: 6794597. Cheryan, M., 1980. Phytic acid interactions in food systems. CRC Crit. Rev. Food Sci. Nutr., 13: 297-335. Cho, C.Y., 1990. Fish nutrition, feeds, and feeding: with special emphasis on salmonid aquaculture. Food Rev. lnt., 6: 333-357. Cho, C.Y., 1992. Feeding systems for rainbow trout and other salmonids with reference to current estimates of energy and protein requirements. Aquaculture, 100: 107-123. Clancy, G.S., 1992. Effect of spoilage and processing conditions on the nutritive value of various marine protein sources for rainbow trout (Oncorhynchus mykiss) and chinook salmon (Oncorhynchus rshawytscha), MSc. Thesis, University of British Columbia, Vancouver, B.C., 215 pp. Clarke, W.C., Virtanen, E., Blackbum, J. and Higgs, D.A., 1994. Effects of dietary betaine/amino acid additive on growth and seawater adaptation in yearling chinook salmon. Aquaculture, 121: 137-145. EaIes, J.G., MacLatchy, D.L., Higgs, D.A. and Dosanjh, B.S., 1992. The influence of dietary protein and caloric content on thyroid function and hepatic thyroxine 5’-monodeiodinase activity in rainbow trout, Oncorhynchus mykiss. Can. J. Zool., 70: 1526-1535. Erdman, J.W. Jr., 1979. Oilseed phytates: nutritional implications. J. Am. Oil. Chem. Sot., 56: 736-741. Fagerlund, U.H.M., Higgs, D.A., McBride, J.R., Archdekin, C., Dosanjh, B.S. and Eales, J.G., 1987. Nutritional value of canola meal protein for juvenile coho salmon (Oncorhynchus kisutch). 8th Prog. Rep., Research on canola seed, oil, meal and meal fractions, Canola Council of Canada, Winnipeg, MB., pp. 5-13. Hajen, W.E., Higgs, D.A., Beames, R.M. and Dosanjh, B.S., 1993. Digestibility of various feedstuffs by postjuvenile chinook salmon (Oncorhynchus tshawytscha) in sea water. 2. Measurement of digestibility. Aquaculture, 112: 333-348. Higgs, D.A., 1986. Feeding fish efficiently. Can. Aquacult. Mag., 2(2): 15, 17, 18.26. Higgs, D.A., Marketi, J.R., MacQuanie, D.W., McBride, J.R., Dosanjh, B.S., Nichols, C. and Hoskins, G., 1979. Development of practical diets for coho salmon, Oncorhynchus kisurch, using poultry-by-product meal, feather meal, soybean meal and rapeseed meal as major protein sources. In: J.E. Halver and K. Tiews (Editors), Finfish Nutrition and Fishfeed Technology, Vol. 2, Heenemann Verlagsgesellschaft mbH, Berlin, pp. 191218. Higgs, D.A., McBride, J.R., Markert, J.R., Dosanjh, B.S., Plotnikoff, M.D. and Clark, W.C., 1982. 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