Apparent digestibility of invertebrate biomasses by rainbow trout

Aquaculture, 50 (1985) 103-112 Elsevier Science Pub~~he~ B. V, , Amsterdam - Printed in The Netherlands

APPARENT DIGESTIBILITY BY RAINBOW TROUT

OF INVERTEBRATE

103

BIOMASSES

J. DE LA NOUE’ and G. CHOUBERT2 ‘Centre de Recherche en Nutrition and Dgpartement de Biologic, Universit& Lava& @&bee, Gl K 7P4 (Canada) z~aborato~re de Nut~t~o~ des Poissons, Centre de Re~herches ~ydrob~ologiques, INRA, it-Pee-sur-Nivel~e, 64310 Ascain (France) (Accepted 2 August 1985)

ABSTRACT De la Noiie, J. and Choubert, G., 1985. Apparent digestibility of invertebrate biomasses by rainbow trout. Aquaculture, 50: 103-112. This study was aimed at comparing the apparent digestibility of chironomid larvae, daphnid, and gammarid biomasses by rainbow trout and characterizing the amino acid profiles of each of these food sources. Rainbow trout were fed twice daily on a reference diet (91.5% fish meal) and three other diets con~i~ng 30% of chironomids, daphnids or gammarids and 70% reference diet (dry weight basis). Dry matter, crude protein, energy content and chromic oxide were determined in diets and feces and the amino acid composition of the food was established. The digestibility of energy showed decreasing values from the reference diet to daphnids, the chironomids and the gammarids (89.7, 80.6, 73.6 and 65.3% respectively). For crude protein, the results were essentially the same; the daphnids and chironomids gave the same apparent digestibility coefficient (82.6 and 83.6% respectively).

INTRODUCTION

Invertebrates are the main food source for salmonids in the natural env~onment. For example, daphnids can represent up to 98% of the total food for trout during certain periods of the year (Galbr~th, 1967). Several other invertebrates have been found to be valuable sources of protein for fish (Watanabe et al., 1978; Yurkowski and Tabachek, 1979). It was therefore appropriate to compare the digestibility of daphnid biomass to that of gammarids and chironomid larvae. These invertebrate biomasses can be obtained from the natural environment (Mathias et al., 1982), cultured (Shaw and Mark, 1980; Kawasaki et al., 1982; Myrand and De la Noiie, 1983;Proulx and De la Notie, 1985), or purchased. Apart from the work of Elliott (1975a, b), little seems to be known, however, about the nutritional value of these protein sources for fish (Smith et al., 1980). One potenti~ly interesting solution is to incorporate protein 0044~8486/85/$03.30

o 1985 Elsevier Science Publishers B.V.

104

from invertebrate biomasses, especially daphnids obtained through biological recycling of wastewaters by intensive systems (Kawasaki et al., 1982; Proulx, 1984), into the food ration. On the basis of approximate composition of these animal biomasses one would predict good potential for their inclusion in fish food (Proulx and De la Noiie, 1985), or as live food for fish larvae and fry. The amino acid composition of the protein source (NCR, 1981) is one of the most important factors to be considered in fish nutrition. Hence, the second goal of the present study was to characterize the amino acid profile of each of the invertebrate biomasses that were used. MATERIALS

AND METHODS

The experiments were done with 63-70-g (initial weight) rainbow trout (Sulmo guirdneri Rich.); 15 individuals were kept in each of six 60-l cylindroconical tanks (1.0 kg fish/tank). Water temperature was 19 _+1°C. Four types of food were used in succession. These were (1) a reference diet [91.5% fish meal, 1% mineral mix (Luquet, 1971); 3% vitamin mix (EIFAC, 1971); 1% lignosulphite; 2% alginate; 1.5% chromic oxide], (2) a reference : daphnid diet (70 : 30, w/w dry wt basis), (3) a reference : chironomid larvae diet (70 : 30 w/w, dry wt basis) and (4) a reference : gammarid diet (70 : 30, w/w, dry wt basis). In the text, these diets will be refered to as daphnid diet, chronomid diet and gammarid diet, respectively. The daphnids were collected in a natural water body near Sete, France. The gammarids and the chironomid larvae were purchased at Lyard (F73370 LeBourget du Lac) and Gresbil (F95880 Enghien-les-Bains) productions, respectively. All the invertebrate biomasses were lyophilised before their incorporation into the diets. After an adaptation period of 15 days to the tanks, the fish were fed twice daily (9.00 a.m. and 4.00 p.m.) with their respective diets at a level of 1.5% of their live weight/day. Non-ingested food was collected, dried and weighed. The fish were adapted for 2 days to their food (De la Noiie et al., 1980) and then the feces were quantitatively collected from the third day on using an automatic fish feces collector (Choubert et al., 1982). The frozen collected feces were pooled for each tank over a period of 5 days. Thereafter they were lyophilised, weighed and finely ground. Dry matter was measured by drying at 95°C for 24 h or until a constant weight was achieved. Crude protein was determined by Kjel-Foss, energy content by a Parr adiabatic bomb microcalorimeter and chromic oxide by the procedure described by Bolin et al. (1952). The amino acid profiles of the invertebrate biomasses were determined with an LKB amino acid analyzer after acid hydrolysis with 6 N HCl at 100°C for 24 h. The apparent digestibility coefficients (ADC) for dry matter, crude protein and energy were calculated by the following formula (Maynard and Loosli, 1969) :

105

ACD=lOO

l[

% nutrient

in feces x % CrJ& in diet

% nutrient

in diet

% Cr,O, in feces

1

The apparent digestibility coefficient for a given invertebrate contribution was measured according to Cho and Slinger (1979) as: (ADC of test diet - 0.7 ADC of reference

biomass

diet)/0.3.

Data were processed through classical methods of variance analysis (Snedecor and Cochran, 1980). Significant differences were established using Student’s “t” test. RESULTS

The dry matter, crude protein and energy content of the various diets and protein sources are presented in Table I. The dietary chromic oxide content of invertebrate diets, also shown in Table I, was found to be approximately the same as calculated (1.05%) except for the daphnid diet, for which a somewhat higher value was obtained (1.16%). The diets were comparable in their crude protein contents (60-67s dry weight), gammarid and chironomid diets showing the lowest values. The energy content was similar for all diets. Table 2 gives the amino acid composition of the protein sources used. The three invertebrate biomasses showed similar amino acid patterns with the notable exception of chironomid larvae which had a histidine content (10.64 mg/lOO mg dry matter) more than ten times higher than that measured in daphnids or gammarids. Quantitatively, the total amino acid content increased in the following order: gammarids < daphnids < chironomids < reference diet. The levels of total and essential amino acids in gammarids were about half those in the reference diet. TABLE 1 Dry matter, chromic oxide, crude protein and energy content of the diets and invertebrate sources (M % * SD, N = 4) Diet or protein source

Dry matter (% f.w.)a

Cr,O,

Diet 1 Diet 2 (daphnid) Diet 3 (chironomid) Diet 4 (gammarid) Chironomids Daphnids Gammarids

92.1 93.7 91.7 91.7 -

1.47 1.16 1.09 1.04 -

af.w. : fresh weight. bd.w. : dry weight. CCalculated values.

+ i t *

0.3 0.6 0.4 0.6

(% d.w.)b t * * *

0.12 0.06 0.04 0.06

N x 6.25 (% d.w.)

Energy @J/g d-w.)

66.7 65.8 61.5 59.9 49.5 56.2 48.4

19.81 r 20.00 f 19.07 f 19.02 t 17.33c 20.43’= 17.16c

* + * +

2.0 0.9 0.8 1.2

0.42 0.79 0.44 0.38

106 TABLE 2 Total amino acid content and the reference diet Amino acid

Leucine Isoleucine Lysine Threonine Tryptophane VaIine Methionine Phenylalanine Histidine Arginine Cystine Tyrosine Serine Alanine Aspartic acid Glutamic acid Glycine Proline NH, Total essentialb Total non-essentialc*d Totalb,c,d

(mg/lOO g dry matter) in each of the invertebrate biomasses

Reference diet 5.41 3.45 4.89 2.75 z3 2.20 3.22 1.32 3.51 3.79 2.49 2.89 4.01 5.61 8.03 3.53 2.69 1.12 30.84 30.35 61.19

El

Chironomids (diet 3)

Daphnids (diet 2)

2.68 1.93 3.00 1.85 n.m. 2.14 0.83 3.63 10.64 2.42 0.69 1.48 2.04 2.78 4.09 5.47 1.84 n.m. 0.91 29.12 18.39 47.51

3.33 2.07 2.92 2.24 n.m. 2.45 0.98 3.39 0.96 2.85 0.52 1.75 2.14 2.64 4.09 5.45 1.99 n.m. 0.94 21.19 18.59 39.77

Gammarids (diet 4) 2.28 1.43 1.80 1.40 ::; 0.60 3.79 0.60 2.11 0.59 1.11 1.42 2.18 3.05 4.21 1.74 n.m. 0.98 15.73 14.30 30.03

%m. : not measured. bExcluding tryptophane. CExcluding proline. d Excluding N&.

In the reference diet, the greatest amino acid contribution was from glutamic acid, aspartic acid, leucine and lysine. In chironomid larvae, the dominant amino acids were histidine and glutamic and aspartic acids. In gammarids, glutamic acid and phenylalanine were the most abundant amino acids, whereas in daphnids these were glutamic and aspartic acids. Histidine was at lowest concentration in the reference diet, whereas the levels of cystine and methionine were lowest in chironomid larvae; histidine, cystine and methionine were lowest in gammarids and daphnids. The amount of feces collected (Table 3) varied in the following order: reference diet < chironomid diet < daphnid diet < gammarid diet, the last yielding almost twice the quantities measured with the reference diet. The major difference observed for the feces obtained from fish fed the four diets pertained to the Cr,O, content. The apparent digestibility coefficients for the four diets and the invertebrate biomasses are presented in Table 4. For dry matter, crude protein

107 TABLE 3 Weight, crude protein, energy and chromic

oxide contents of feces (M ?- SD, N = 6)

Component

Reference diet

Daphnids (diet 2)

Chironomids (diet 3)

Gammarids (diet 4)

Ingested food (g d.m./5 days) Feces (d.m.) (g/5 days) Cr,G, (% d.m.) Crude protein (% d.m.) Energy (kJ/g d.m.)

69.1

70.3

68.8

68.8

12.35a * 0.39 6.89’ +0.22 32.2a ltO.88 9.52a f 0.61

17.27b ~0.62 4.55c *O.lO 31.9a t1.11 11.29c eO.24

16.46b kO.58 4.24b *0.08 28.8b to.65 11.20b +0.27

21.93c +0.65 3.36e +0.07 27.8c to.65 10.79d + 0.29

a,bc,dValues bearing the same letter in a given row are not significantly (P > 0.05) different. TABLE 4 Apparent digestibility coefficients measured for the reference diet, the diets incorporating invertebrate biomasses and calculated for the invertebrate biomasses (Mean % * SD, N=6) Diet or component

Dry matter

Nitrogen + 6.25

Energy

Diet 1 Diet 2 (daphnid) Diet 3 (chironomid) Diet 4 (gammarid) Chironomids Daphnids Gammarids

78.7 74.5 74.3 69.0 63.9 64.6 46.3

89.7 87.6 87.9 85.6 83.6 82.6 75.9

89.7 87.0 84.9 82.4 73.6 80.6 65.3

f * f. +

0.48a 0.36b 0.24b 0.45c

f 0.26a ?: 0.2gb f 0.18b +_0.42c

t * + i

0.84a 0.38c 0.35b 0.5gd

a*b*c*dValuesbearing the same letter in a given column are not significantly (P > 0.05) different.

and energy, the reference diet gave the highest digestibility. The daphnid diet came next with significantly (P < 0.01) lower values (2%) for crude protein and energy and with significantly (P < 0.01) lower results (4%) for dry matter. The lowest digestibilities were obtained with the gammarid diet, for which significantly (P < 0.01) smaller values were measured for energy (-7.3% as compared to the reference diet), crude protein (-4.1%) and dry matter (-9.7%). From the digestibility data obtained for the mixed diets incorporating invertebrate biomasses, apparent digestibility coefficients of test ingredients alone were calculated (Table 4). It can be seen that daphnids gave higher digestibility coefficients than chironomid larvae (except for crude protein

108

which was 1% lower). Gammarids biomass in terms of the digestibility

appeared to be a much inferior quality of dry matter, crude protein and energy.

DISCUSSION

Although evaluating the nutritional value of substitutes for fish meal becomes increasingly necessary, there is as yet no agreement between laboratories with respect to the methodology to be used for digestibility studies. Although this basic difficulty precludes many useful comparisons, the results obtained can be sufficiently indicative to retain or rule out some of the tested substitutes. In order to feed nutritionally balanced diets, we chose to use diets containing 70% of a reference diet and 30% of substitution test products as did Cho and Slinger (1979). One of the factors to be considered in substituting invertebrate biomasses for fish meal in diets for fish is their origin (Watanabe et al., 1978) and the time of the year of their harvesting. Their biochemical composition may vary significantly on a seasonal basis (Sadykhov et al., 1975) and heat processing of biomasses has consequences for the digestibility of protein and amino acids, whereas lyophilisation is without effect (Opstvedt et al., 1984). It is also important to consider the collection strategy used, selective versus non-selective, as this will have consequences on the composition of the biomass. This is especially true for Duphnia, since a difference of 1000 Cal/g dry weight has been reported between reproductive females and immature individuals (Richman, 1958), the former showing a much higher fat content than the latter (Birge and Juday, 1922). The non-selective mode of harvesting might help in minimizing the possible variations in nutritional quality of the biomass. In general, the amino acid composition of invertebrates is quite variable (see Yurkowski and Tabachek, 1979). The amino acid composition of the daphnid biomass used in the present work, which was collected from the natural environment, is virtually identical to that of Daphnia grown on wastewaters (Proulx and De la Noiie, 1985) and non-selectively harvested. The total amino acid composition (excluding tryptophane and proline) of the daphnid biomass used in our study was about the same as that reported by Dabrowski and Rusiecki (1983) for Daphnia pulex (0.61-0.95 mm length; 41.46 mg total amino acid/100 mg dry weight). This figure is, however, lower than that reported for bigger D. pulex (0.95-1.35 mm length) by these authors, who measured a total amino acid content of 51.06 mg/lOO mg dry weight. The different species or strains used in different laboratories may of course explain this discrepancy, as shown by Yurkowski and Tabachek (1979). The amino acid composition of the gammarid biomass (30.03 mg total amino acid/100 mg dry weight) reported here was lower than the compositions reported by Mathias et al. (1982), which amounted to 38.040.3 mg amino acid/100 mg dry solids (including 1.8-1.9 mg proline/ 100 mg).

The chironomid larvae biomass showed the highest total amino acid content (47.51 mg/lOO mg dry weight). If we compare the amino acid profile obtained with that reported by Yurkowski and Tabachek (1979) for chironomids, the most striking difference is related to the histidine content, which is very high in our case. There is no obvious explanation for this discrepancy. It is interesting to note that all the invertebrate biomasses used in the present study satisfy the requirements for essential amino acids of salmonids (NRC, 1981). In the case of gammarids, the only relative deficiencies that could arise are for lysine, which was 1.8 mg/lOO mg dry weight, compared to a desirable level of 2.1 according to Halver (1976), and arginine (2.1 vs 2.5 mg/lOO mg dry weight according to the same author). The amino acid composition of these invertebrate biomasses is appropriate to meet the needs of salmonids; this is in line with the fact that these fish may feed heavily on daphnids (Galbraith, 1967), gammarids (Mathias et al., 1982) or chironomids (Frost, 1977) in the natural environment. For reference diet, which showed the highest digestibility for dry matter (78.7%), the quantity of feces collected was the least. The daphnid and chironomid larvae diets had similar dry matter digestibility and the amounts of feces collected were not significantly different. For the gammarid diet, the dry matter digestibility was much lower (69.0%) and the fecal output was the greatest (Table 3). This is a good indication that the methodology used for the collection of feces was quantitatively satisfactory. Despite the relatively low digestibility for dry matter measured for the gammarid biomass in the present study, it is worth noting that the dry matter digestibility for the gammarid diet was about the same as that reported for other trout feeds by Cho and Slinger (1979) and De la Noiie et al. (1980). The digestibility coefficient of crude protein for the reference diet (Table 4) was significantly higher (P < 0.01) than the values obtained for the chironomid and daphnid diets, which were themselves significantly higher (P < 0.01) than that measured for the gammarid diet. Although the inclusion of invertebrate biomasses lowered somewhat the digestibility coefficients for crude protein in the resulting mixtures, these biomasses generally showed better apparent digestibilities than other feed substitutes of animal origin (Cho and Slinger, 1979), namely feather meal (62.3%), poultry by-product meal (69.2%) and blood meal (39.8%) or Pruteen (digestibility coefficients of 7&O-82.4% for proteins; Luquet and Kaushik, 1978). The energy content of the three invertebrate biomasses was about the same (Table l), but the digestibility of the energy varied. This might be explained by the chitin content. Chitin is known to be difficult for fish to digest (Lindsay et al., 1984) and is present in large quantities in the invertebrates used, i.e. 4% in chironomid larvae, 7% in daphnids (Yurkowski and Tabachek, 1979) and around 7% in Gammarus lacustris (Mathias et al., 1982). The results obtained for the digestibility of energy (Table 4) show sig-

110

nificantly (P < 0.01) decreasing values from the reference diet to the daphnid, the chironomid and, finally, the gammarid diet. Despite the lower performance of fish fed diets containing invertebrates, the values obtained were still higher than those reported for trout receiving conventional diets (Cho and Slinger, 1979; De la Noiie et al., 1980) where energy digestibility amounted to only 70-75%. For the substitution components considered alone, chironomid larvae and daphnids gave high digestibility compared to substitutes from commercial ingredients as reported by Cho and Slinger (1979). Gammarids were the only invertebrates that gave less satisfactory results with respect to energy digestibility. In conclusion, the results obtained for the digestibility of diets containing chironomid, daphnid or gammarid biomasses, showed that such sources can be utilized efficiently by juvenile rainbow trout. It would be interesting to assess through digestibility studies the nutritional value of these biomasses for fish larvae and fry, especially as live food. An adaptation of the collection technique of the feces used in the present work should be used since it allows digestibility measurement by the direct method. ACKNOWLEDGMENTS

We wish to thank M.P. Luquet for his interest in the present work and for providing us with the facilities of the Fish Nutrition Laboratory (INRA, Saint-Pee-sur-Nivelle, France). Thanks are expressed to Mr. G. Barnabe who provided us with the daphnid biomass. We thank T. Pouliot for his excellent assistance, Dr. P. Ross for useful criticisms, and D. Ni Eidhin for improving the style. This work was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Fonds FCAC of the Ministere de 1’Education du Quebec; a travel grant was provided to Joel de la Noiie for work at the Fish Nutrition Laboratory (INRA, Saint-Pee-sur-Nivelle, France) by the France-Quebec exchange program.

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112 Watanabe, T., Arakawa, C., Kitajima, C. and Fujita, S., 1978. Nutritional evaluation of proteins of living feeds used in seed production of fish. Bull. Jpn. Sot. Sci. Fish., 44: 985-988. Yurkowski, M. and Tabachek, J.L., 1979. Proximate and amino acid composition of some natural fish foods. In: J. Halver and K. Tiews (Editors), Proc. World Symp. on Finfish Nutrition and Fishfeed Technology, Vol. I. Heenemann, Berlin, pp. 435-448,