- Email: [email protected]
Chelated zinc reduces the dietary zinc requirement of channel catfish, Ictalurus punctatus
Aquaculture ELSEVIER
Aquaculture
133 ( 1995) 73-82
Chelated zinc reduces the dietary zinc requirement of channel catfish, Ictalurus punctatus ’ Tippawan Paripatananont,
Richard T. Love11 *
Departmentof Fisheries and Allied Aquacultures, Auburn University, Accepted
14 December
Auburn,
AL 36849 USA
1994
Abstract The dietary zinc requirements of year-l channel catfish were determined with an egg-white-based purified diet and with a soybean-meal-based practical diet, each supplemented with serial concentrations of zinc methionine ( ZnMet) or zinc sulfate heptahydrate ( ZnS). In the egg white diet, supplemental dietary zinc requirements, determined by broken-line regression analysis, for ZnMet and ZnS for maximum weight gain were 5.58 and 18.94 mg/kg, respectively, and for maximum bone zinc deposition were 6.58 and 19.91 mg/kg, respectively. In the soybean meal diet, supplemental dietary zinc requirements for ZnMet and ZnS for maximum weight gain were 5.91 and 30.19 mg/kg, respectively, and for maximum bone zinc deposition were 12.82 and 2 80 mg/kg, respectively. The relative bioavailabilities of ZnMet, with ZnS as the standard, were 352% for weight gain and 305% for bone zinc deposition in the egg white diet, and 482% for weight gain and 586% for bone zinc deposition in the soybean meal diet. This experiment showed that ZnMet has approximately 3 times the potency of ZnS in a purified diet and 4-5 times the potency of ZnS in a practical diet containing phytic acid for meeting the dietary zinc requirements of channel catfish. Kqvwords: Zinc methionine; Zinc sulfate; lctlcrurus puncfutus; Growth fish; Bone zinc deposition
1. Introduction
Zinc is required by animals for a number of biochemical processes. Channel catfish fed zinc-deficient diets show reduced growth rate, anorexia, reduced serum zinc, and reduced bone zinc and calcium deposition (National Research Council, 1993). The zinc requirement of channel catfish has been determined to be 20 mg/kg in purified diets (Gatlin and Wilson, * Corresponding author. ’ Part of this information
wzx presented
in a popular article in Aquuculture
pp. 66-68. 0044~8486/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDlOO44-8486(94)00404-8
Muguzine, March/April 1994,
14
T. Paripatananont,
R.T. Love11 /Aquaculture
133 (1995) 73-82
1983) and 150 mg/kg in practical (phytate-containing) diets (Gatlin and Wilson, 1984). These requirements were determined with zinc sulfate as the source of supplemented zinc. Amino-acid-chelated zinc has been shown to have a higher absorption rate in animal intestine than inorganic forms of zinc, such as zinc carbonate, zinc sulfate, and zinc oxide (Ashmead, 1992). Wedekind et al. (1992) reported that the bioavailability of zinc from zinc methionine (ZnMet) in poultry was greater than that of zinc sulfate and the difference in bioavailability increased as complexity of the diet increased. The bioavailability of ZnMet relative to that of zinc sulfate was 117% in a crystalline amino acid purified diet and 206% in a complex corn-soybean diet. Hardy and Shearer (1992) found that feeding a zinc-amino acid chelate resulted in greater zinc deposition in body tissues than zinc sulfate or zinc sulfateEDTA in low calciumphosphorus diets but not in high calcium-phosphorus diets. Gomes and Kaushik (1993) replaced inorganic zinc with ZnMet in rainbow trout diets containing vegetable or animal proteins and found no difference in zinc concentrations in plasma, whole body or viscera between fish fed the two sources of zinc. There is no information on the effects of organic and inorganic sources of dietary zinc on growth or zinc deposition in channel catfish. The objective of this study was to determine the dietary zinc requirement of channel catfish with ZnMet and zinc sulfate (ZnS) and to compare the bioavailability of the two zinc sources, using a purified egg-white-based diet and a practical soybean-meal-based diet.
2. Materials and methods Experimental design and diets Two basal diets were used in the experiment, an egg-white-based diet and a practical type, soybean-meal-based diet (Table 1) . The egg-white-based diet was supplemented with 0, 5, 10, 15, or 30 mg of zinc/kg from either ZnMet (Zinpro, Chaska, MI) or zinc sulfate heptahydrate (ZnSO,. 7H02, Fisher Scientific, Norcross, GA). The egg white diets were formulated from purified ingredients to contain 34% crude protein and 3.1 kcal of digestible energy/g based on tabular values of the diet ingredients provided by the National Research Council ( 1993) and ICN Nutritional Biochemicals (Irvine, CA). The spray-dried egg white was obtained from ICN Nutritional Biochemicals, and the other ingredients were obtained from United States Biochemical Corp. (Cleveland, OH). The egg white diets were prepared as 3-mm diameter, semi-moist (approximately 30% moisture) pellets as described by El Naggar and Love11 ( 199 1) . Additional biotin was included in the egg white diet to compensate for biotin binding of avidin (Scarpa and Gatlin, 1992). Diets were stored at - 18°C and thawed in a refrigerator for 24 h before feeding. The soybean-meal-based diets were supplemented with 0,5, 10,20, or 80 mg of zinc/kg from either ZnMet or ZnS. The soybean meal diets were formulated to contain 32% crude protein and 2.9 kcal/g, based on tabular values for the diet ingredients (National Research Council, 1993)) and prepared as semimoist pellets and stored at - 18°C. The diets were analyzed for crude protein by the macroKjeldahl method (Association of the Official Analytical Chemists, 1984) and for zinc by an inductively-coupled argon plasma spectrometer (ICAP Model 9000, Jarrell-Ash Division, Fisher Scientific Company, Waltham, MA) using the procedure described by the manufacturer.
T. Paripatananont, Table 1 Composition
R.T. Lovell/Aquaculture
133 (1995) 73-82
75
of the basal diets
Ingredient
Egg white diet (g/kg)
Spray-dried egg white Dextrin Cellulose Biotin Corn oil Cod liver oil Calcium carbonate Zinc-free mineral mixa Vitamin mix” Ascorbic acid polyphosphate’ Soybean meal Cottonseed meal Corn Wheat Carboxymethylcellulose
400.0 370.0 100.5 0.0005 30.0 30.0 12.0 40.0 14.0 3,s
Soybean meal diet (g/kg)
30.0 30.0 12.0 40.0 14.0 3.5 550.0 145.0 110.0 45.5 20.0
Yontains (as g/kg ofpremix): FeS0,.7Hz0, 5.0; MgS0,.7H,O, 132.0; K2HP0,, 240.0; NaH,P0,.H20, 231.0; NaCI, 45.0; AICl, .6H,O, 0.15, CuSO,. 5Hz0, 0.5; MnSO, HzO, 0.7; CoClz. 6HZ0, I .O; Na,SeO,, 0.0 II; celhlose, 344.49 ( McClain and Gatlin, 1988). “Provides the following diluted in cellulose (mg/kg of diet): thiamin, 10; choline, 500; niacin, 150; riboflavin, 20; pyridoxine, 20; calcium pantothenate, 200; vitamin B,Z, 0.06; retinyl acetate (500 000 IU/g), 12; cY-tocopherol, 50; cholecalciferol ( 1 000 000 ICU/g), 1; menadione Na-bisulfite, 80; inositol, 400; biotin, 1. “Sourceof ascorbic acid polyphosphate( 15%ascorbicacid) was HoffmanLa Roche (Basel, Switzerland).
Fish andfeeding
trials
Newly-hatched channel catfish, Zctalurus punctatus, from a single egg mass from the Alabama Agricultural Experiment Station were brought into the fish nutrition laboratory at the Auburn University Fisheries Research Unit and maintained on a vitamin-refortified commercial salmon starter diet for 3 weeks. The fish were subsequently stocked into 40liter aquaria (50 fish per aquarium) which were supplied with a continuous flow of sandfiltered water from a IO-ha reservoir. Water flow rate through each aquarium was 1 l/min and temperature was maintained at 28 f2”C. A 12-h light/ 12-h dark photoperiod was maintained. Zinc concentration in the water flowing into the aquaria was 19 &l as determined by ICAP spectrophotometry. The fish were fed a zinc-depleted egg-white-based diet (Table 1) for 2 weeks after which time 3 aquaria of fish were randomly assigned to each of the 18 experimental diets. The fish were fed twice daily to satiation for 10 weeks. Handling procedures and facilities were in compliance with the guidelines of the Animal Care and Use Committee of Auburn University. When a bacterial infection occurred in any aquarium, fish in all aquaria were given a 1-h static bath in an aqueous solution of oxytetracycline at 20 mg/l (Sigma Chemical Co.) followed by two additional treatments at 3-day intervals. At the end of the experimental period, the fish were counted and weighed and 3 fish from each aquarium were sampled, killed by pithing the brain and frozen at - 60°C for subsequent zinc analysis of vertebrae. The frozen fish were thawed at room temperature, heated in a microwave oven for 3 min, and the flesh was removed from the vertebrae. The vertebrae were boiled in distilled water
76
T. Paripatananont,
R.T. Love11 /Aquaculture
133 (1995) 73-82
for 10 min to remove remaining soft tissue and oven-dried for 2 h at 125°C. The dried bones were ground, ashed and prepared for atomic absorption analysis as described by Campbell and Plank ( 1992). The zinc concentration was determined with the ICAPspectrometer. Statistical analysis Weight gain and bone zinc content data were analyzed using the General Linear Model procedures of SAS (1987) to establish the regression of weight gain or bone zinc content on increasing level of dietary zinc. Where the regression was non-linear, the data were analyzed by the broken line regression procedure (Robbins et al., 1979; Robbins, 1986) to determine the breakpoint in the response curve which represents the optimum dietary concentration of zinc. The linear segments of the regression lines below the breakpoints were used to compare the bioavailability of zinc from &Met with that from ZnS by deriving the ratio of the slopes of the lines (Forbes and Parker, 1977).
3. Results white diet The amount of zinc in the egg white basal diet was 1.6 mglkg. Fish fed the basal diet showed anorexia, extremely poor growth and markedly low bone zinc content in comparison with the fish fed the diets with zinc supplements (Table 2). There was no difference in mortality among the treatments and mean survival for all fish fed egg white diets was 98.1%. Weight gain and apparent feed efficiency responded in a quadratic manner to increases in zinc supplementation with both sources of zinc (P < 0.01). Apparent feed efficiency values increased approximately in proportion to increases in weight gains for both sources of zinc. There were significant differences in the slopes and breakpoints in the weight gain regression lines for the two zinc sources. The regression of weight gain on dietary zinc supplementation Egg
Table 2 Weight gain, apparent feed efficiency and bone zinc content of channel catfish fed various levels of supplemental zinc from zinc methionine ( ZnMet) or zinc sulfate ( ZnS) in egg-white-based diets for 10 weeks Supplemental
zinc
Weight gain (g)”
Apparent feed efficiency gain/g feed)”
ZnMet
ZnS
ZnMet
ZnS
ZnMet
ZnS
2.4 22.1 22.5 24.3 26.3 0.78 Q(P
2.4 12.3 16.6 19.7 25.6 0.59 Q(P
0.33 0.67 0.67 0.70 0.7 I 0.024 Q(P
0.33 0.41 0.54 0.62 0.73 0.017 Q(P
73.7 I S8.2 166.5 176.9 211.0 10.37 Q(f
73.7 101.7 129.0 162.7 203.2 8.11 Q(PiO.01)
(mg/kg)
0 5 IO 15 30 Pooled SEM Regression
“Means of 3 replicate groups. Average intial weight of fish was “Means of 8 fish.
I .07 g.
(g
Bone zinc (pg/g)
h
T. Paripatananont, R.T. Lmell /Aquaculture 133 (1995) 73-82
17
30 bkpt = 18.94 mgikg
bkpt = 5.58 mg/kg
.____________----------.:
--ZnMet .-__$7nS
L
0
5
10
SUPPLEMENTAL
Fig. 1.Regression of weight gain on supplemental egg-white-based diets containing zinc methionine
~
15
-_
20
~~
25
30
DIETARY ZINC (mgkg)
dietary zinc and breakpoints in the lines for channel catfish fed (ZnMet) or zinc sulfate (ZnS).
was markedly greater for ZnMet than for ZnS (Fig. 1) The breakpoint in the regression line, which was considered to be the minimum dietary concentration for optimum response, for ZnMet was 5.58 mg zinc/kg diet and the breakpoint for ZnS was 18.94 mglkg. The regression of bone zinc deposition on dietary zinc was also quadratic for both zinc sources (P < 0.01) (Table 2). There were significant differences in the slopes and breakpoints in the regression lines for the two zinc sources (Fig. 2). The breakpoint for ZnMet occurred at 6.58 mg zinc/kg diet and that for ZnS occurred at 19.91 mg/kg. The ratios of the slopes of the regression lines below breakpoints were 3.52 (3.94/ 1.12) for weight gain and 3.05 ( 16.89/5.53) for bone zinc deposition. The bioavailability of zinc from ZnMet in relation to that from ZnS was 352% (3.52 X 100) for weight gain and 305% (3.05 X 100) for bone zinc deposition (Table 4). .
Soybean meal diet
The amount of zinc in the soybean meal basal diet was 46.1 mg/kg. Apparently this amount was not sufficiently available to meet the requirement of the fish because the fish fed the basal diet were more anorexic and weight gain and bone zinc content were markedly
bkpt = 6.58 mgikg
m . _,C_____________-------~ ..-
,_/’
” bkpt = 19.91 mg/kg
*aMet .---ZnS
01
0
5
10
SUPPLEMENTAL
15
20
30
DIETARY ZINC (mg:g)
Fig. 2. Regression of bone zinc deposition on supplemental catfish fed egg-white-based diet containing zinc methionine
dietary zinc and breakpoints in the lines for channel (ZnMet) or zinc sulfate ( ZnS).
78
T. Paripatananont,
R.T. Love11 /Aquaculture
133 (1995) 73-82
Table 3 Weight gain, apparent feed efficiency and bone zinc content of channel catfish fed various levels of supplemental zinc from zinc methionine (&Met) or zinc sulfate (ZnS) in soybean-meal-based diets for 10 weeks Supplemental
zinc
Weight gain
(g )”
(mglkg)
Apparent feed efficiency (g gain/g feed)”
Bone zinc (pglg)”
ZnMet
ZnS
ZnMet
ZnS
ZnMet
ZnS
3.9 20.0 22.4 22.4 24.1 1.05 Q(P
3.9 7.8 10.8 17.5 24.4 0.61 Q(P
0.28 0.63 0.65 0.64 0.68 0.029 Q(P~0.01)
0.31 0.36 0.40 0.64 0.75 0.023 Q(P
96.6 160.6 176.2 193.7 219.8 18.60 Q(P
96.6 107.6 114.1 136.5 208.3 9.82 L(P
0 5 10 20 80 Pooled SEM Regression
“Means of 3 replicate groups. Average initial fish weight was 1.07 g. ‘Means of 8 fish.
lower than those of the fish fed zinc supplements (Table 3). There was no difference in mortality among the treatments and mean survival for all fish fed soybean meal diets was 98.4%. Weight gain of fish fed the soybean meal basal diet was nearly the same as that of fish fed the egg white basal diet. Weight gain and apparent feed efficiency of fish fed the soybean meal diets supplemented with ZnMet or ZnS increased quadratically with increases in dietary zinc (P < 0.01). Increases in apparent feed efficiency were approximately in proportion to the increases in weight gain for both sources of zinc. The slopes and breakpoints in the weight gain regression lines were significantly different for the two zinc sources. The breakpoint in the regression line for ZnMet was 5.91 mg/kg and that for ZnS was 30.19 mg/kg (Fig. 3). The regression of bone zinc deposition on dietary content of ZnMet was quadratic (P < 0.01) ; however, the regression of bone zinc deposition on dietary content of ZnS was linear (P < 0.01) (Fig. 4). The breakpoint in the bone zinc regression line for ZnMet was 12.82 mg supplemental zinc/kg diet. Because there was a continuous linear
30 bkpt = 5.91 mgikg
bkpt = 30.19 mg/kg
01 0
SO
&PLEkENTL D&AR:oz1Nc~nlglk;;
Fig. 3. Regression of weight gain on supplemental dietary zinc and breakpoints in the lines for channel cattish fed soybean-meal-based diets containing zinc methionine ( ZnMet) or zinc sulfate ( ZnS) .
T. Paripatananont. R.T. Lovell/Aquaculture
I33 (1995) 73-82
79
$ % bkp: = 12.82 me/kg
0
10
20
30
SUPPLEMENTAL
40
50
M)
70
so
DIETARY ZINC (mg/kg)
Fig. 4. Regression of bone zinc deposition on supplemental dietary zinc and breakpoints in the lines for channel catfish fed soybean-meal-based diets containing zinc methionine (ZnMet) or zinc sulfate (ZnS). Table 4 Dietary zinc requirements for growth and bone zinc deposition determined with zinc methionine (ZnMet) and zinc sulfate (ZnS) and relative bioavailability of ZnMet compared to ZnS in channel catfish fed egg white (EW) and soybean-meal( SBM)-based diets Criterion
Diet
Zinc source
Zinc” requirement
Weight gain
EW
ZnMet ZnS ZnMet ZnS ZnMet ZIIS ZnMet ZnS
5.58 18.94 5.91 30.19 6.58 19.91 12.82 280
SBM Bone zinc
EW SBM
“Breakpoint in the regression line. bathe ratio of the slope of ZnMet regression
(mg/kg
diet)
line to the slope of ZnS regression
Relativeb bioavailability
(%)
352 482 305 586
line X
100.
regression of bone zinc on all levels of dietary ZnS, a breakpoint could not be established. However, bone zinc content was not significantly different in fish fed 80 mg supplemental zinc/kg (the highest concentration) from ZnMet and fish fed 80 mg zinc/kg from ZnS. The ratios of the slopes of the regression lines below breakpoints were 4.82 (3.2310.67) for weight gain and 5.86 (7.97/1.36) for bone zinc deposition. The bioavailability of zinc from &Met in relation to that from ZnS was 482% (4.82 X 100) for weight gain and 586% (5.86 X 100) for bone zinc deposition (Table 4).
4. Discussion The dietary zinc requirement for channel catfish varied with zinc source, diet and criterion measured. In the egg white diet, which contained 1.6 mg zinc/kg, weight gain of fish fed ZnS increased as the dietary zinc level increased up to the breakpoint at 18.94 mg/kg. This
80
T. Paripatananont,
R.T. Love11 /Aquaculture
133 (1995) 73-82
was relatively similar to the National Research Council ( 1993) zinc requirement for channel catfish of 20 mg/kg which is based upon data obtained by Gatlin and Wilson ( 1983) with ZnS in an egg-white-based diet. However, when ZnMet was the zinc source, the requirement for optimum growth was only 5.58 mg/kg. The zinc requirements for optimum bone zinc deposition from ZnMet and ZnS were 6.58 and 19.91 mg/kg, respectively, and were similar to the requirements for weight gain, These values indicated that the young channel catfish required approximately 3 times more zinc in the inorganic form than in the organic form. The relative bioavailability values of ZnMet when compared to ZnS for weight gain, 352%, and bone zinc, 305%, accurately described the difference in these sources of zinc in meeting the dietary needs of young channel catfish. The supplemental zinc allowance for optimum weight gain from ZnMet was similar in the soybean meal diet and the egg white diet; however, the supplemental zinc allowance for optimum weight gain from ZnS was markedly higher in the soybean meal diet. There was a similar trend when zinc allowances for bone zinc deposition were compared; the zinc allowance from ZnS was approximately 4 times higher in the soybean meal diet than in the egg white diet whereas the allowance from ZnMet was approximately 2 times higher in the soybean meal diet. Gatlin and Wilson (1984) fed channel catfish ZnS and found that the zinc allowance should be higher in a soybean-meal-based diet than in an egg white diet, apparently because the zinc was complexed with phytic acid (Lo et al., 1981; Spinelli et al., 1983; McClain and Gatlin, 1988). Data from the present study indicate that zinc from ZnMet has less affinity for complexing with phytic acid than zinc from ZnS. Wedekind et al. (1992) found that the potency of ZnMet relative to ZnS for tibia zinc deposition in chickens was 117% when fed in a crystalline amino acid purified diet but was 206% when fed in a corn-soybean meal diet. Ashmead ( 1992) claimed that the higher bioavailability of amino-acid-bound trace elements to animals is because chelation protects the element from forming insoluble complexes in the digestive tract and by facilitating zinc transport across the intestinal mucosa. He also suggested that the chelate may remain intact until it reaches the site in the body where the element is needed. Spears (1989) found that zinc from ZnMet and zinc oxide (ZnO) were absorbed similarly in lambs, but that zinc retention was higher in animals fed ZnMet. He interpreted this to indicate that zinc from the two sources is utilized differently after absorption. No reports were found in the literature where zinc requirements were established for other animals with chelated zinc fed in highly purified diets. Wedekind et al. ( 1992) found that weight gain in chickens fed ZnMet in a crystalline amino acid purified diet increased linearly only up to 6 mg of zinc/kg diet, but that birds fed ZnS showed a linear increase in weight gain through the highest dietary concentration of zinc which was 9 mg/kg. The soybean-meal-based practical diet contained 46 mg/kg, yet the fish grew poorly. A supplement to this diet of only 5.91 mg/kg of zinc from ZnMet was sufficient for normal growth. This indicates the poor availability of zinc in soybean meal, and possibly other plant feedstuffs for channel catfish. A supplement of 150 mg zinc/kg diet was necessary to meet the zinc requirement of channel catfish fed soybean-meal-based diets containing ZnO (Gatlin and Wilson, 1984). Wedekind et al. (1992) reported that ZnO had 61% of the bioavailability of ZnS for chickens fed a corn-soybean meal diet. Therefore, the requirement
T. Paripatananont,
R.T. Love11 /Aquaculture
133 (1995) 73-82
81
of supplemental zinc from ZnS in practical diets for channel catfish may be lower than 150 mg/kg, perhaps near 90 mg/kg ( 150 mg/kg X 61%). This experiment showed that ZnMet has approximately 3 times the potency of ZnS in a purified diet and 4-5 times the potency of ZnS in practical diets containing phytic acid. This means that the dietary allowance of zinc in catfish feeds can be reduced by using the chelated zinc instead of the inorganic form.
Acknowledgements The authors wish to thank Dr. John C. Williams for his help with the regression analysis of the data.
References Ashmead, H.D., 1992. The Roles of Amino Acid Chelates in Animal Nutrition. Noyes Publications, New Jersey, 419 pp. Association of the Official Analytical Chemists, 1984. Method of Analysis, AOAC, Washington, DC, 1141 pp. Campbell, CR. and Plank, C.O., 1992. Organic matter destruction: dry ashing. In: CO. Plank (Editor), Plant Analysis Reference Procedures for the Southern Region of the United States, The Georgia Agricultural Experiment Stations, College of Agricultural and Environmental Sciences, Southern Cooperative Series Bulletin 368. El Naggar, G.O. and Lovell, R.T., 1991. L-Ascorbyl-2-monophosphate has equal antiscorbutic activity as Lascorbic but L-ascorbyl-2-sulphate is inferior to L-ascorbic acid for channel catfish. J. Nun., 121: 1622-1626. Forbes, R.M. and Parker, H.M., 1977. Biological availability of zinc in and as influenced by whole fat soy flour in rat diets. Nutr. Rep. Int., 15: 681-689. Gatlin, D.M., III and Wilson, R.P., 1983. Dietary zinc requirement of fingerling channel catfish. J. Nutr., 113: 630-635. Gatlin, D.M., III and Wilson, R.P., 1984. Zinc supplementation of practical channel catfish diets. Aquaculture, 41: 31-36. Gomes, E.F. and Kaushik, S.J., 1993. Effect of replacement of dietary inorganic zinc by zinc methionine on vegetable and animal protein utilization by rainbow trout. In: S.J. Kaushik and P.J. Luquet (Editors), Fish Nutrition in Practice: 4th International Symposium on Fish Nutrition and Feeding, Bianitz, France, June 2427, 199 1, pp.897-902. Hardy, R.W. and Shearer, K.D., 1992. The use of zinc amino acid chelates in high calcium and phosphorus diets of rainbow trout. In: H.D. Ashmead (Editor), The Roles of Amino Acid Chelates in Animal Nutrition. Noyes Publications, New Jersey, pp. 424-439. Lo. G.S., Settle, S.L., Steinke. F.H. and Hopkins, D.T., 1981. Effect of phytate: zinc molar ratio and isolated soybean meal protein on zinc bioavailability. J. Nutr., 1 I I: 2223-2235. McClain, W.R. and Gatlin, D.M., 111, 1988. Dietary zinc requirement of Oreochromisaureus andeffects of dietary calcium and phytate on zinc bioavailability. J. World Aquacult. Sot., 19: 103-108. National Research Council, 1993. Nutrient Requirements of Fish. National Academy Press, Washington, DC, 114 PP. Robbins, K.R., 1986. A method, SAS program, and examples for fitting the broken line to growth data. Univ. Tenn. Res. Rep. 8609. Univ. of Tenn. Agric. Exp. Sta., Knoxville. Robbins, K.R., Norton, H.W. and Baker, D.H., 1979. Estimation of nutrient requirements from growth data. J. Nutr., 109: 1710-1714. SAS, 1987. SAS User’s Guide. SAS Institute, Gary, NC. Scarpa, J. and Gatlin, D.M., III, 1992. Zinc supplementation of practical channel catfish diets. Aquaculture, 41: 31-36.
82
T. Paripufananont,
R. T. Love11 /Aquaculture
133 (I 995) 73-82
Spears, J.W., 1989. Zinc methionine for ruminants: relative bioavailability of zinc in lambs and effects of growth and performance of growing heifers. J. Anim. Sci., 67: 835-843. Spinelli, J., Home, C.R. and Wekell, J.C., 1983. The effect of phytates on the growth of rainbow trout (Sa[mo gairdneri) fed pure diets containing varying quantities of calcium and magnesium. Aquaculture, 30: 71-83. Wedekind, K.J., Hottin, A.E. and Baker, D.H., 1992. Methodology for assessing zinc bioavailability: efficacy estimates for zinc-methionine, zinc sulfate, and zinc oxide. J. Anim. Sci., 70: 178-187.
Aquaculture
133 ( 1995) 73-82
Chelated zinc reduces the dietary zinc requirement of channel catfish, Ictalurus punctatus ’ Tippawan Paripatananont,
Richard T. Love11 *
Departmentof Fisheries and Allied Aquacultures, Auburn University, Accepted
14 December
Auburn,
AL 36849 USA
1994
Abstract The dietary zinc requirements of year-l channel catfish were determined with an egg-white-based purified diet and with a soybean-meal-based practical diet, each supplemented with serial concentrations of zinc methionine ( ZnMet) or zinc sulfate heptahydrate ( ZnS). In the egg white diet, supplemental dietary zinc requirements, determined by broken-line regression analysis, for ZnMet and ZnS for maximum weight gain were 5.58 and 18.94 mg/kg, respectively, and for maximum bone zinc deposition were 6.58 and 19.91 mg/kg, respectively. In the soybean meal diet, supplemental dietary zinc requirements for ZnMet and ZnS for maximum weight gain were 5.91 and 30.19 mg/kg, respectively, and for maximum bone zinc deposition were 12.82 and 2 80 mg/kg, respectively. The relative bioavailabilities of ZnMet, with ZnS as the standard, were 352% for weight gain and 305% for bone zinc deposition in the egg white diet, and 482% for weight gain and 586% for bone zinc deposition in the soybean meal diet. This experiment showed that ZnMet has approximately 3 times the potency of ZnS in a purified diet and 4-5 times the potency of ZnS in a practical diet containing phytic acid for meeting the dietary zinc requirements of channel catfish. Kqvwords: Zinc methionine; Zinc sulfate; lctlcrurus puncfutus; Growth fish; Bone zinc deposition
1. Introduction
Zinc is required by animals for a number of biochemical processes. Channel catfish fed zinc-deficient diets show reduced growth rate, anorexia, reduced serum zinc, and reduced bone zinc and calcium deposition (National Research Council, 1993). The zinc requirement of channel catfish has been determined to be 20 mg/kg in purified diets (Gatlin and Wilson, * Corresponding author. ’ Part of this information
wzx presented
in a popular article in Aquuculture
pp. 66-68. 0044~8486/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDlOO44-8486(94)00404-8
Muguzine, March/April 1994,
14
T. Paripatananont,
R.T. Love11 /Aquaculture
133 (1995) 73-82
1983) and 150 mg/kg in practical (phytate-containing) diets (Gatlin and Wilson, 1984). These requirements were determined with zinc sulfate as the source of supplemented zinc. Amino-acid-chelated zinc has been shown to have a higher absorption rate in animal intestine than inorganic forms of zinc, such as zinc carbonate, zinc sulfate, and zinc oxide (Ashmead, 1992). Wedekind et al. (1992) reported that the bioavailability of zinc from zinc methionine (ZnMet) in poultry was greater than that of zinc sulfate and the difference in bioavailability increased as complexity of the diet increased. The bioavailability of ZnMet relative to that of zinc sulfate was 117% in a crystalline amino acid purified diet and 206% in a complex corn-soybean diet. Hardy and Shearer (1992) found that feeding a zinc-amino acid chelate resulted in greater zinc deposition in body tissues than zinc sulfate or zinc sulfateEDTA in low calciumphosphorus diets but not in high calcium-phosphorus diets. Gomes and Kaushik (1993) replaced inorganic zinc with ZnMet in rainbow trout diets containing vegetable or animal proteins and found no difference in zinc concentrations in plasma, whole body or viscera between fish fed the two sources of zinc. There is no information on the effects of organic and inorganic sources of dietary zinc on growth or zinc deposition in channel catfish. The objective of this study was to determine the dietary zinc requirement of channel catfish with ZnMet and zinc sulfate (ZnS) and to compare the bioavailability of the two zinc sources, using a purified egg-white-based diet and a practical soybean-meal-based diet.
2. Materials and methods Experimental design and diets Two basal diets were used in the experiment, an egg-white-based diet and a practical type, soybean-meal-based diet (Table 1) . The egg-white-based diet was supplemented with 0, 5, 10, 15, or 30 mg of zinc/kg from either ZnMet (Zinpro, Chaska, MI) or zinc sulfate heptahydrate (ZnSO,. 7H02, Fisher Scientific, Norcross, GA). The egg white diets were formulated from purified ingredients to contain 34% crude protein and 3.1 kcal of digestible energy/g based on tabular values of the diet ingredients provided by the National Research Council ( 1993) and ICN Nutritional Biochemicals (Irvine, CA). The spray-dried egg white was obtained from ICN Nutritional Biochemicals, and the other ingredients were obtained from United States Biochemical Corp. (Cleveland, OH). The egg white diets were prepared as 3-mm diameter, semi-moist (approximately 30% moisture) pellets as described by El Naggar and Love11 ( 199 1) . Additional biotin was included in the egg white diet to compensate for biotin binding of avidin (Scarpa and Gatlin, 1992). Diets were stored at - 18°C and thawed in a refrigerator for 24 h before feeding. The soybean-meal-based diets were supplemented with 0,5, 10,20, or 80 mg of zinc/kg from either ZnMet or ZnS. The soybean meal diets were formulated to contain 32% crude protein and 2.9 kcal/g, based on tabular values for the diet ingredients (National Research Council, 1993)) and prepared as semimoist pellets and stored at - 18°C. The diets were analyzed for crude protein by the macroKjeldahl method (Association of the Official Analytical Chemists, 1984) and for zinc by an inductively-coupled argon plasma spectrometer (ICAP Model 9000, Jarrell-Ash Division, Fisher Scientific Company, Waltham, MA) using the procedure described by the manufacturer.
T. Paripatananont, Table 1 Composition
R.T. Lovell/Aquaculture
133 (1995) 73-82
75
of the basal diets
Ingredient
Egg white diet (g/kg)
Spray-dried egg white Dextrin Cellulose Biotin Corn oil Cod liver oil Calcium carbonate Zinc-free mineral mixa Vitamin mix” Ascorbic acid polyphosphate’ Soybean meal Cottonseed meal Corn Wheat Carboxymethylcellulose
400.0 370.0 100.5 0.0005 30.0 30.0 12.0 40.0 14.0 3,s
Soybean meal diet (g/kg)
30.0 30.0 12.0 40.0 14.0 3.5 550.0 145.0 110.0 45.5 20.0
Yontains (as g/kg ofpremix): FeS0,.7Hz0, 5.0; MgS0,.7H,O, 132.0; K2HP0,, 240.0; NaH,P0,.H20, 231.0; NaCI, 45.0; AICl, .6H,O, 0.15, CuSO,. 5Hz0, 0.5; MnSO, HzO, 0.7; CoClz. 6HZ0, I .O; Na,SeO,, 0.0 II; celhlose, 344.49 ( McClain and Gatlin, 1988). “Provides the following diluted in cellulose (mg/kg of diet): thiamin, 10; choline, 500; niacin, 150; riboflavin, 20; pyridoxine, 20; calcium pantothenate, 200; vitamin B,Z, 0.06; retinyl acetate (500 000 IU/g), 12; cY-tocopherol, 50; cholecalciferol ( 1 000 000 ICU/g), 1; menadione Na-bisulfite, 80; inositol, 400; biotin, 1. “Sourceof ascorbic acid polyphosphate( 15%ascorbicacid) was HoffmanLa Roche (Basel, Switzerland).
Fish andfeeding
trials
Newly-hatched channel catfish, Zctalurus punctatus, from a single egg mass from the Alabama Agricultural Experiment Station were brought into the fish nutrition laboratory at the Auburn University Fisheries Research Unit and maintained on a vitamin-refortified commercial salmon starter diet for 3 weeks. The fish were subsequently stocked into 40liter aquaria (50 fish per aquarium) which were supplied with a continuous flow of sandfiltered water from a IO-ha reservoir. Water flow rate through each aquarium was 1 l/min and temperature was maintained at 28 f2”C. A 12-h light/ 12-h dark photoperiod was maintained. Zinc concentration in the water flowing into the aquaria was 19 &l as determined by ICAP spectrophotometry. The fish were fed a zinc-depleted egg-white-based diet (Table 1) for 2 weeks after which time 3 aquaria of fish were randomly assigned to each of the 18 experimental diets. The fish were fed twice daily to satiation for 10 weeks. Handling procedures and facilities were in compliance with the guidelines of the Animal Care and Use Committee of Auburn University. When a bacterial infection occurred in any aquarium, fish in all aquaria were given a 1-h static bath in an aqueous solution of oxytetracycline at 20 mg/l (Sigma Chemical Co.) followed by two additional treatments at 3-day intervals. At the end of the experimental period, the fish were counted and weighed and 3 fish from each aquarium were sampled, killed by pithing the brain and frozen at - 60°C for subsequent zinc analysis of vertebrae. The frozen fish were thawed at room temperature, heated in a microwave oven for 3 min, and the flesh was removed from the vertebrae. The vertebrae were boiled in distilled water
76
T. Paripatananont,
R.T. Love11 /Aquaculture
133 (1995) 73-82
for 10 min to remove remaining soft tissue and oven-dried for 2 h at 125°C. The dried bones were ground, ashed and prepared for atomic absorption analysis as described by Campbell and Plank ( 1992). The zinc concentration was determined with the ICAPspectrometer. Statistical analysis Weight gain and bone zinc content data were analyzed using the General Linear Model procedures of SAS (1987) to establish the regression of weight gain or bone zinc content on increasing level of dietary zinc. Where the regression was non-linear, the data were analyzed by the broken line regression procedure (Robbins et al., 1979; Robbins, 1986) to determine the breakpoint in the response curve which represents the optimum dietary concentration of zinc. The linear segments of the regression lines below the breakpoints were used to compare the bioavailability of zinc from &Met with that from ZnS by deriving the ratio of the slopes of the lines (Forbes and Parker, 1977).
3. Results white diet The amount of zinc in the egg white basal diet was 1.6 mglkg. Fish fed the basal diet showed anorexia, extremely poor growth and markedly low bone zinc content in comparison with the fish fed the diets with zinc supplements (Table 2). There was no difference in mortality among the treatments and mean survival for all fish fed egg white diets was 98.1%. Weight gain and apparent feed efficiency responded in a quadratic manner to increases in zinc supplementation with both sources of zinc (P < 0.01). Apparent feed efficiency values increased approximately in proportion to increases in weight gains for both sources of zinc. There were significant differences in the slopes and breakpoints in the weight gain regression lines for the two zinc sources. The regression of weight gain on dietary zinc supplementation Egg
Table 2 Weight gain, apparent feed efficiency and bone zinc content of channel catfish fed various levels of supplemental zinc from zinc methionine ( ZnMet) or zinc sulfate ( ZnS) in egg-white-based diets for 10 weeks Supplemental
zinc
Weight gain (g)”
Apparent feed efficiency gain/g feed)”
ZnMet
ZnS
ZnMet
ZnS
ZnMet
ZnS
2.4 22.1 22.5 24.3 26.3 0.78 Q(P
2.4 12.3 16.6 19.7 25.6 0.59 Q(P
0.33 0.67 0.67 0.70 0.7 I 0.024 Q(P
0.33 0.41 0.54 0.62 0.73 0.017 Q(P
73.7 I S8.2 166.5 176.9 211.0 10.37 Q(f
73.7 101.7 129.0 162.7 203.2 8.11 Q(PiO.01)
(mg/kg)
0 5 IO 15 30 Pooled SEM Regression
“Means of 3 replicate groups. Average intial weight of fish was “Means of 8 fish.
I .07 g.
(g
Bone zinc (pg/g)
h
T. Paripatananont, R.T. Lmell /Aquaculture 133 (1995) 73-82
17
30 bkpt = 18.94 mgikg
bkpt = 5.58 mg/kg
.____________----------.:
--ZnMet .-__$7nS
L
0
5
10
SUPPLEMENTAL
Fig. 1.Regression of weight gain on supplemental egg-white-based diets containing zinc methionine
~
15
-_
20
~~
25
30
DIETARY ZINC (mgkg)
dietary zinc and breakpoints in the lines for channel catfish fed (ZnMet) or zinc sulfate (ZnS).
was markedly greater for ZnMet than for ZnS (Fig. 1) The breakpoint in the regression line, which was considered to be the minimum dietary concentration for optimum response, for ZnMet was 5.58 mg zinc/kg diet and the breakpoint for ZnS was 18.94 mglkg. The regression of bone zinc deposition on dietary zinc was also quadratic for both zinc sources (P < 0.01) (Table 2). There were significant differences in the slopes and breakpoints in the regression lines for the two zinc sources (Fig. 2). The breakpoint for ZnMet occurred at 6.58 mg zinc/kg diet and that for ZnS occurred at 19.91 mg/kg. The ratios of the slopes of the regression lines below breakpoints were 3.52 (3.94/ 1.12) for weight gain and 3.05 ( 16.89/5.53) for bone zinc deposition. The bioavailability of zinc from ZnMet in relation to that from ZnS was 352% (3.52 X 100) for weight gain and 305% (3.05 X 100) for bone zinc deposition (Table 4). .
Soybean meal diet
The amount of zinc in the soybean meal basal diet was 46.1 mg/kg. Apparently this amount was not sufficiently available to meet the requirement of the fish because the fish fed the basal diet were more anorexic and weight gain and bone zinc content were markedly
bkpt = 6.58 mgikg
m . _,C_____________-------~ ..-
,_/’
” bkpt = 19.91 mg/kg
*aMet .---ZnS
01
0
5
10
SUPPLEMENTAL
15
20
30
DIETARY ZINC (mg:g)
Fig. 2. Regression of bone zinc deposition on supplemental catfish fed egg-white-based diet containing zinc methionine
dietary zinc and breakpoints in the lines for channel (ZnMet) or zinc sulfate ( ZnS).
78
T. Paripatananont,
R.T. Love11 /Aquaculture
133 (1995) 73-82
Table 3 Weight gain, apparent feed efficiency and bone zinc content of channel catfish fed various levels of supplemental zinc from zinc methionine (&Met) or zinc sulfate (ZnS) in soybean-meal-based diets for 10 weeks Supplemental
zinc
Weight gain
(g )”
(mglkg)
Apparent feed efficiency (g gain/g feed)”
Bone zinc (pglg)”
ZnMet
ZnS
ZnMet
ZnS
ZnMet
ZnS
3.9 20.0 22.4 22.4 24.1 1.05 Q(P
3.9 7.8 10.8 17.5 24.4 0.61 Q(P
0.28 0.63 0.65 0.64 0.68 0.029 Q(P~0.01)
0.31 0.36 0.40 0.64 0.75 0.023 Q(P
96.6 160.6 176.2 193.7 219.8 18.60 Q(P
96.6 107.6 114.1 136.5 208.3 9.82 L(P
0 5 10 20 80 Pooled SEM Regression
“Means of 3 replicate groups. Average initial fish weight was 1.07 g. ‘Means of 8 fish.
lower than those of the fish fed zinc supplements (Table 3). There was no difference in mortality among the treatments and mean survival for all fish fed soybean meal diets was 98.4%. Weight gain of fish fed the soybean meal basal diet was nearly the same as that of fish fed the egg white basal diet. Weight gain and apparent feed efficiency of fish fed the soybean meal diets supplemented with ZnMet or ZnS increased quadratically with increases in dietary zinc (P < 0.01). Increases in apparent feed efficiency were approximately in proportion to the increases in weight gain for both sources of zinc. The slopes and breakpoints in the weight gain regression lines were significantly different for the two zinc sources. The breakpoint in the regression line for ZnMet was 5.91 mg/kg and that for ZnS was 30.19 mg/kg (Fig. 3). The regression of bone zinc deposition on dietary content of ZnMet was quadratic (P < 0.01) ; however, the regression of bone zinc deposition on dietary content of ZnS was linear (P < 0.01) (Fig. 4). The breakpoint in the bone zinc regression line for ZnMet was 12.82 mg supplemental zinc/kg diet. Because there was a continuous linear
30 bkpt = 5.91 mgikg
bkpt = 30.19 mg/kg
01 0
SO
&PLEkENTL D&AR:oz1Nc~nlglk;;
Fig. 3. Regression of weight gain on supplemental dietary zinc and breakpoints in the lines for channel cattish fed soybean-meal-based diets containing zinc methionine ( ZnMet) or zinc sulfate ( ZnS) .
T. Paripatananont. R.T. Lovell/Aquaculture
I33 (1995) 73-82
79
$ % bkp: = 12.82 me/kg
0
10
20
30
SUPPLEMENTAL
40
50
M)
70
so
DIETARY ZINC (mg/kg)
Fig. 4. Regression of bone zinc deposition on supplemental dietary zinc and breakpoints in the lines for channel catfish fed soybean-meal-based diets containing zinc methionine (ZnMet) or zinc sulfate (ZnS). Table 4 Dietary zinc requirements for growth and bone zinc deposition determined with zinc methionine (ZnMet) and zinc sulfate (ZnS) and relative bioavailability of ZnMet compared to ZnS in channel catfish fed egg white (EW) and soybean-meal( SBM)-based diets Criterion
Diet
Zinc source
Zinc” requirement
Weight gain
EW
ZnMet ZnS ZnMet ZnS ZnMet ZIIS ZnMet ZnS
5.58 18.94 5.91 30.19 6.58 19.91 12.82 280
SBM Bone zinc
EW SBM
“Breakpoint in the regression line. bathe ratio of the slope of ZnMet regression
(mg/kg
diet)
line to the slope of ZnS regression
Relativeb bioavailability
(%)
352 482 305 586
line X
100.
regression of bone zinc on all levels of dietary ZnS, a breakpoint could not be established. However, bone zinc content was not significantly different in fish fed 80 mg supplemental zinc/kg (the highest concentration) from ZnMet and fish fed 80 mg zinc/kg from ZnS. The ratios of the slopes of the regression lines below breakpoints were 4.82 (3.2310.67) for weight gain and 5.86 (7.97/1.36) for bone zinc deposition. The bioavailability of zinc from &Met in relation to that from ZnS was 482% (4.82 X 100) for weight gain and 586% (5.86 X 100) for bone zinc deposition (Table 4).
4. Discussion The dietary zinc requirement for channel catfish varied with zinc source, diet and criterion measured. In the egg white diet, which contained 1.6 mg zinc/kg, weight gain of fish fed ZnS increased as the dietary zinc level increased up to the breakpoint at 18.94 mg/kg. This
80
T. Paripatananont,
R.T. Love11 /Aquaculture
133 (1995) 73-82
was relatively similar to the National Research Council ( 1993) zinc requirement for channel catfish of 20 mg/kg which is based upon data obtained by Gatlin and Wilson ( 1983) with ZnS in an egg-white-based diet. However, when ZnMet was the zinc source, the requirement for optimum growth was only 5.58 mg/kg. The zinc requirements for optimum bone zinc deposition from ZnMet and ZnS were 6.58 and 19.91 mg/kg, respectively, and were similar to the requirements for weight gain, These values indicated that the young channel catfish required approximately 3 times more zinc in the inorganic form than in the organic form. The relative bioavailability values of ZnMet when compared to ZnS for weight gain, 352%, and bone zinc, 305%, accurately described the difference in these sources of zinc in meeting the dietary needs of young channel catfish. The supplemental zinc allowance for optimum weight gain from ZnMet was similar in the soybean meal diet and the egg white diet; however, the supplemental zinc allowance for optimum weight gain from ZnS was markedly higher in the soybean meal diet. There was a similar trend when zinc allowances for bone zinc deposition were compared; the zinc allowance from ZnS was approximately 4 times higher in the soybean meal diet than in the egg white diet whereas the allowance from ZnMet was approximately 2 times higher in the soybean meal diet. Gatlin and Wilson (1984) fed channel catfish ZnS and found that the zinc allowance should be higher in a soybean-meal-based diet than in an egg white diet, apparently because the zinc was complexed with phytic acid (Lo et al., 1981; Spinelli et al., 1983; McClain and Gatlin, 1988). Data from the present study indicate that zinc from ZnMet has less affinity for complexing with phytic acid than zinc from ZnS. Wedekind et al. (1992) found that the potency of ZnMet relative to ZnS for tibia zinc deposition in chickens was 117% when fed in a crystalline amino acid purified diet but was 206% when fed in a corn-soybean meal diet. Ashmead ( 1992) claimed that the higher bioavailability of amino-acid-bound trace elements to animals is because chelation protects the element from forming insoluble complexes in the digestive tract and by facilitating zinc transport across the intestinal mucosa. He also suggested that the chelate may remain intact until it reaches the site in the body where the element is needed. Spears (1989) found that zinc from ZnMet and zinc oxide (ZnO) were absorbed similarly in lambs, but that zinc retention was higher in animals fed ZnMet. He interpreted this to indicate that zinc from the two sources is utilized differently after absorption. No reports were found in the literature where zinc requirements were established for other animals with chelated zinc fed in highly purified diets. Wedekind et al. ( 1992) found that weight gain in chickens fed ZnMet in a crystalline amino acid purified diet increased linearly only up to 6 mg of zinc/kg diet, but that birds fed ZnS showed a linear increase in weight gain through the highest dietary concentration of zinc which was 9 mg/kg. The soybean-meal-based practical diet contained 46 mg/kg, yet the fish grew poorly. A supplement to this diet of only 5.91 mg/kg of zinc from ZnMet was sufficient for normal growth. This indicates the poor availability of zinc in soybean meal, and possibly other plant feedstuffs for channel catfish. A supplement of 150 mg zinc/kg diet was necessary to meet the zinc requirement of channel catfish fed soybean-meal-based diets containing ZnO (Gatlin and Wilson, 1984). Wedekind et al. (1992) reported that ZnO had 61% of the bioavailability of ZnS for chickens fed a corn-soybean meal diet. Therefore, the requirement
T. Paripatananont,
R.T. Love11 /Aquaculture
133 (1995) 73-82
81
of supplemental zinc from ZnS in practical diets for channel catfish may be lower than 150 mg/kg, perhaps near 90 mg/kg ( 150 mg/kg X 61%). This experiment showed that ZnMet has approximately 3 times the potency of ZnS in a purified diet and 4-5 times the potency of ZnS in practical diets containing phytic acid. This means that the dietary allowance of zinc in catfish feeds can be reduced by using the chelated zinc instead of the inorganic form.
Acknowledgements The authors wish to thank Dr. John C. Williams for his help with the regression analysis of the data.
References Ashmead, H.D., 1992. The Roles of Amino Acid Chelates in Animal Nutrition. Noyes Publications, New Jersey, 419 pp. Association of the Official Analytical Chemists, 1984. Method of Analysis, AOAC, Washington, DC, 1141 pp. Campbell, CR. and Plank, C.O., 1992. Organic matter destruction: dry ashing. In: CO. Plank (Editor), Plant Analysis Reference Procedures for the Southern Region of the United States, The Georgia Agricultural Experiment Stations, College of Agricultural and Environmental Sciences, Southern Cooperative Series Bulletin 368. El Naggar, G.O. and Lovell, R.T., 1991. L-Ascorbyl-2-monophosphate has equal antiscorbutic activity as Lascorbic but L-ascorbyl-2-sulphate is inferior to L-ascorbic acid for channel catfish. J. Nun., 121: 1622-1626. Forbes, R.M. and Parker, H.M., 1977. Biological availability of zinc in and as influenced by whole fat soy flour in rat diets. Nutr. Rep. Int., 15: 681-689. Gatlin, D.M., III and Wilson, R.P., 1983. Dietary zinc requirement of fingerling channel catfish. J. Nutr., 113: 630-635. Gatlin, D.M., III and Wilson, R.P., 1984. Zinc supplementation of practical channel catfish diets. Aquaculture, 41: 31-36. Gomes, E.F. and Kaushik, S.J., 1993. Effect of replacement of dietary inorganic zinc by zinc methionine on vegetable and animal protein utilization by rainbow trout. In: S.J. Kaushik and P.J. Luquet (Editors), Fish Nutrition in Practice: 4th International Symposium on Fish Nutrition and Feeding, Bianitz, France, June 2427, 199 1, pp.897-902. Hardy, R.W. and Shearer, K.D., 1992. The use of zinc amino acid chelates in high calcium and phosphorus diets of rainbow trout. In: H.D. Ashmead (Editor), The Roles of Amino Acid Chelates in Animal Nutrition. Noyes Publications, New Jersey, pp. 424-439. Lo. G.S., Settle, S.L., Steinke. F.H. and Hopkins, D.T., 1981. Effect of phytate: zinc molar ratio and isolated soybean meal protein on zinc bioavailability. J. Nutr., 1 I I: 2223-2235. McClain, W.R. and Gatlin, D.M., 111, 1988. Dietary zinc requirement of Oreochromisaureus andeffects of dietary calcium and phytate on zinc bioavailability. J. World Aquacult. Sot., 19: 103-108. National Research Council, 1993. Nutrient Requirements of Fish. National Academy Press, Washington, DC, 114 PP. Robbins, K.R., 1986. A method, SAS program, and examples for fitting the broken line to growth data. Univ. Tenn. Res. Rep. 8609. Univ. of Tenn. Agric. Exp. Sta., Knoxville. Robbins, K.R., Norton, H.W. and Baker, D.H., 1979. Estimation of nutrient requirements from growth data. J. Nutr., 109: 1710-1714. SAS, 1987. SAS User’s Guide. SAS Institute, Gary, NC. Scarpa, J. and Gatlin, D.M., III, 1992. Zinc supplementation of practical channel catfish diets. Aquaculture, 41: 31-36.
82
T. Paripufananont,
R. T. Love11 /Aquaculture
133 (I 995) 73-82
Spears, J.W., 1989. Zinc methionine for ruminants: relative bioavailability of zinc in lambs and effects of growth and performance of growing heifers. J. Anim. Sci., 67: 835-843. Spinelli, J., Home, C.R. and Wekell, J.C., 1983. The effect of phytates on the growth of rainbow trout (Sa[mo gairdneri) fed pure diets containing varying quantities of calcium and magnesium. Aquaculture, 30: 71-83. Wedekind, K.J., Hottin, A.E. and Baker, D.H., 1992. Methodology for assessing zinc bioavailability: efficacy estimates for zinc-methionine, zinc sulfate, and zinc oxide. J. Anim. Sci., 70: 178-187.