The use of fish silage as an ingredient for eel fingerling nutrition

Aquaculture, 80 (1989) 135-146 Elsevier Science Publishers B.V., Amsterdam

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Printed

in The Netherlands

The Use of Fish Silage as an Ingredient for Eel Fingerling Nutrition JOSE FERNANDO GONCALVES’, SOFIA SANTOS, IRINEU BAPTISTA’ and JOAO COIMBRA’

VICTOR SOUSA PEREIRA’,

‘Institute of Biomedical Sciences “Abel Salazar”, Large do Prof. Abel Salazar 2,400O Porto (Portugal) ‘National Institute of Fisheries Research, Au. Brasilia, 1200 Lisbon (Portugal) (Accepted

12 August 1988)

ABSTRACT Goncalves, J.F., Santos, S., Pereira, V.S., Baptism, I. and Coimbra, J., 1989. The use of fish silage as an ingredient for eel fingerling nutrition. Aquaculture, 80: 135-146. This study was undertaken to test the growth parameters and the body composition of eel fingerlings (1.7 g) fed isoproteic and isocaloric diets with different percentages (lo,15 and 20% ) of protein from fish silage. The incorporation of silage in the diet resulted in an increase in the specific growth rate, the food conversion efficiency and the protein efficiency ratio, when compared to a control population fed only a fish and meat meal, as protein source, during a 4-month period. No differences were seen in the effectiveness of the diets incorporating different percentages of fish silage. The increase in growth rate and the presence of greater amounts of lipids in the carcasses of eels receiving silage are partially due to greater food ingestion, owing probably to a different texture of the ration or the possible presence of food attractants. The pattern of amino acids did not differ much between diets, and the essential amino acids were always present in a sufficient amount. Hence the better food conversion efficiency and protein efficiency ratio (PER) of eels on the diets containing silage probably result from the good quality of the fatty acids present in the silage (great percentage of the w-3 series) and possibly on the greater amount of sodium present.

INTRODUCTION

There is a high demand for eels in virtually every European country, as wild stocks decline due to increased pollution of rivers (Bardach et al., 1972; Bellepaire and Ollevier, 1987). Because of this market demand, eel culture is becoming increasingly important (Vassal and Brusle, 1984; Gallagher and Matthews, 1987). In any eel culture system, it is primarily feeding which determines the success of the operation. In many countries food accounts for an average of 51 to 55% of the expenses of growing eels for the market (Bardach et al., 1972; De-

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hapiot, 1980). The formulation of an economical and nutritious eel feed is therefore important for the success of aquaculture (Gallagher and Matthews, 1987 ) . Industrial feeds for eels are characterized by high protein (not less than 50% ) and fat contents and a low crude fibre content (Koops and Kuhlmann, 1976; Descamps et al., 1981). As for other fish (Page and Andrews, 1973), fingerling feeds are higher in protein than feeds for larger eels (Koops, 1979 ). Generally high quality fish meal is used as a protein source (Bardach et al., 1972; Koops, 1979). Due to the high price of this raw material, one of the main investigations in developing a commercial eel culture industry is the development of feeds based on local ingredients (EIFAC, 1985). In Portugal, one possible cheap source of protein for eel nutrition is fish silage, obtained from residues from the fishing and canned fish industries. The spread of these industries, and the existence of excellent conditions for eel culture throughout the country (Coimbra, 1985; Bessa, 1987), mean that fish silage could become an ingredient for eel food in Portugal. The objective of this work was to test the specific growth rate, the efficiency of food conversion, the digestibility and other basic parameters related to growth and body composition of eels fed isoproteic and isocaloric diets, but with different percentages of protein from fish silage. MATERIAL AND METHODS

The facilities included 20 tanks each of 50 1, with mechanical and biological filtration, decantation and UV sterilization, the total volume being 2 m3 (1000 1 for the tanks and 1000 1 for the filtration unit) (Fig. 1) . In the filters, tropical plants (genus Drucaena) were incorporated in order to reduce nitrate accumulation. The total system had a flow of 1000 l/h, and a photoperiod of 12 h, with a light intensity of 20 lux for the tanks and 100 lux for the plants. The stock was randomly distributed (Table 1). Four feeding regimes were compared (four tanks for each regime). The four diets were isoenergetic and isoproteic. The energetic content of the different components of the diets was calculated by the use of a calorimetric bomb (Parr 1341). A 5th diet of commercial origin was used for comparison with our control. Increasing percentages of fish and meat meal were substituted by silage from sardine and blue whiting at lo,15 and 20% of the total protein in the dry matter, which corresponds to incorporations up to 55% in the wet matter for the diet with 20% total protein substitution (Tables 2 and 3 ). The pH of all the diets was adjusted to 6.3, which was the pH of the control diet. The feeding rate was 2% of body weight (dry weight), distributed in two meals a day. Mortality was registered daily, and the specific growth rate and the effi-

137

Fig. 1. Layout of the experimental unit: 1, biological filters; 2, UV sterilizer; 3, tanks; 4, sedimentation unit; 5 and 6, mechanical filters; 7, collector.

TABLE 1 Experimental conditions at the start Diets

Total wt. (g) Initial indiv. wt. (g) Initial no. of fish Stock density ( kg/m3)

Control

SlO%

S15%

S20%

Commercial

126.5 1.73 73 2.5

122.6 1.70 73 2.5

128.4 1.77 73 2.6

129.2 1.77 73 2.6

125.2 1.72 73 2.6

TABLE 2 Diet components Control

SlO%

S15%

S20%

Fish silage Blood meal Meat meal Fish meal Wheat meal

5.0 21.0 39.5 2.0

9.0 5.0 12.6 37.8 2.6

12.8 5.0 11.7 34.5 1.5

17.0 5.0 10.5 31.5 -

Soybean Dried skim milk Distillers solubles Mineral and vitamin complex Binder

22.5 1.5 5.0 1.5 2.0

19.5 5.0 5.0 1.5 2.0

21.0 5.0 5.0 1.5 2.0

12.5 5.0 15.0 1.5 2.0

138 TABLE 3

(% in dry weight) and energy content

Diet composition

Crude protein Lipids Ash Ca P Energy

(kJ/g)

(kJ/g)

Control

SlO%

S15%

S20%

Commercial

49.8 9.1 13.8 4.80 1.61

49.7 9.5 12.6 3.74 1.26

49.9 9.4 12.5 3.38 1.22

49.4 9.8 12.0 2.92 1.20

49.0 9.3 12.4 -

17.63

16.66

17.51

16.46

17.85

TABLE 4 Chemical parameters

Ammonia (NH: Nitrites (NO,) Nitrates

)

of the water after passing biofilters

(w/l) (mg/l) (mg/l)

(water in) and fish tanks (water out)

Water out

Water in

0.183-0.206 0.147-0.169 0.155-0.232

0.131-0.151 0.101-0.141 0.122-0.190

ciency of food conversion were evaluated every month, after weighing and measuring all the stock. The chemical water parameters were controlled. The water temperature was constant and approximately 24’ C. The pH of the water varied between 6.5 and 7.1; ammonia, nitrite and nitrate levels were very low (Table 4). Dissolved O2 varied between 6.8 and 8.0 mg/l. The experiment lasted for 4 months. A digestibility test, using the classical technique of incorporating chromium in the food, and some carcass analysis were carried out. F and t tests were used to evaluate the differences of the means. RESULTS

Growth Fig. 2 shows the growth (medium individual weight) of eels fed each of the five diets. Each point represents the mean of the four replicates. After the fourth month the weight of the eels fed diets containing silage was significantly higher than that of eels fed the control diet. The growth of eels fed the commercial diet was lower than all the others (Table 5). Mortality of the stock was not too high (21% ), and most of it was due to eels escaping from the tanks. The specific growth rates (SGR) of the five groups are summarized in Table 6. The results reinforce the reported differences.

139

months 4

Commercial

--g Control

hSlO%

+

s 15%

-6S20%

Fig. 2. Growth (g) over a 4-month period.

TABLE 5 Growth (g ) and standard deviation (S ) 1st Month

2nd Month

3rd Month

4th Month

x s n

1.699 0.148 266

2.087 0.173 218

2.098 0.184 178

2.147 0.119 128

Ic

1.812 0.078 271

2.023 0.063 239

2.195 0.112 187

2.420”~~ 0.076 128

1.893 0.280 267

2.242 0.148 218

2.455 0.233 176

2.561”~~ 0.196 128

1.922 0.173 275

2.319 0.241 237

2.457 0.167 182

2.572”.b 0.173 128

1.677 0.082 264

1.817 0.102 237

1.902 0.127 175

1.953” 0.102 128

Diet Control

SlO%

S

n S15%

x S

n S20%

i S

n Commercial

5 S

n

“Different from control. bDifferent from commercial diet.

140 TABLE 6 Specific growth rate = ( (In wt - In wO)/t ). 100 where t= time of the experiment w = weight

(128 days) and

Control

SlO%

S15%

S20%

Commercial

-0.315 0.595 0.005 0.073

0.188 0.320 0.288 0.323

0.194 0.498 0.324 0.141

0.229 0.552 0.206 0.154

- 0.082 0.236 0.163 0.088

Total

0.165

0.280

0.289

0.291

0.095

s(k)

0.04

0.03

0.06

0.05

0.04

1st Month 2nd Month 3rd Month 4th Month

TABLE 7 Apparent

s(k)

food conversion

efficiency

Control

SlO%

S15%

S20%

12.7 3.5

8.6 1.3

9.0 2.3

8.7 2.0

TABLE 8 Ingested food evaluation Diet

No. of eels

Feeding rate (% live weight)

Ingestion (% total food)

Control SlO% S15% S20%

128 128 128 128

2 2 2 2

69.8 79.9 79.8 88.9

Food conversion efficiency (FCE) The apparent food conversion efficiencies of the animals fed the four diets, during the 4 months of the experiment, are presented in Table 7. To estimate the food conversion efficiency, the percentage of ingested food was evaluated in a l-week experiment reproducing the general conditions reported, but utilizing silos in order to retrieve the wasted food in an easier way. The results of these experiments are reported in Table 8. These results allowed the mean individual FCE to be calculated for each of the diets (Table 9). The FCE of the diets with silage was higher than the

141 TABLE 9 Calculated food conversion

s(k)

efficiency

Control

SlO%

S15%

S20%

8.87 2.46

6.00” 0.93

6.26” 1.57

6.10” 1.38

“Different from control. TABLE 10 Digestibility Diet

Control SlO% S15% S20%

evaluation No. of eels

128 128 128 128

Feeding rate ( % live weight )

Digestibility

2 2 2 2

38.8 41.9 31.1 -

(%o)

TABLE 11 Protein efficiency ratio (PER)

s(i)

Control

SlO%

S15%

S20%

Commercial

0.24 0.067

0.34 0.057

0.34 0.097

0.34 0.091

0.11 0.023

control, but there was no difference percentages of silage.

between

the diets containing

different

Digestibility

The results from a l-week evaluation of the digestibility of the different using chromic oxide (Cr,O,) as a marker are shown in Table 10.

Protein efficiency

diets

ratio (PER)

The protein efficiency ratio (weight gain/protein ingested) for each diet is shown in Table 11. The protein efficiency ratio was the same for the different diets containing silage but was lower in the control.

142 TABLE 12 Amino acid analysis of the different diets (g/100 g) Amino acid

Control

SlO%

S15%

S20%

Aspartic Threonine Serine Glutamic acid Proline Glycine Alanine Cystine Valine Methionine Isoleucine Leucine Thyamine Phenylalanine Histidine Lysine

9.37 4.21 4.43 14.99 6.59 8.61 6.79 0.34 5.76 2.44 4.03 8.06 3.09 4.58 3.15 7.25

9.72 4.27 4.46 14.45 5.89 7.16 6.31 0.48 5.68 2.34 4.09 7.93 3.42 4.43 2.74 7.31

9.81 4.14 4.16 14.44 5.78 6.80 6.18 0.54 5.76 2.34 4.13 7.62 3.34 4.37 2.76 7.08

9.76 4.17 4.29 14.19 5.72 6.77 6.16 0.63 5.71 2.30 4.12 7.45 3.24 4.59 2.70 6.90

TABLE 13 Fatty acid composition of “blue whiting” silage (% ) c 9:o c1o:o Cll:O c12:o c13:o c14:o c15:o C15:l C16:O C16: 1 C16:l C16:3 C16:4 c17:o C18:O C18:l C18:l C18:2

(~9) (~7) (04) (01)

(w9) (~7) (~6)

0.32 0.00 0.36 0.20 0.00 1.35 0.34 0.13 27.60 0.26 1.95 0.31 0.13 0.34 6.23 31.37 2.36 14.00

C18:3 (~3) C18:4 (1x3) c2o:o C2O:l (wll) C2O:l (0x3) C2O:l (w7) C20: 4 (~6) C20:5 (~03) C21:3 (~6) c22:o C22:l (011) C22:l (us) C22:5 (~3) C22:6 (~3) C24:O C24: 1 (-_) Unknown

0.27 0.49 0.49 0.82 0.76 0.15 0.31 1.56 0.42 0.43 0.63 0.89 0.36 2.48 0.39 0.45 1.52

143 TABLE 14 Carcass analysis ( % ) for crude protein (CP ) and fat

CPilha, CP final ACP 128dsyss Fatinitial

Fatfinal A Fat 128daysa

Control

SlO%

S15%

S20%

Commercial

68.5 65.4 -5.0 14.2 25.9 12.0

68.5 66.1 -3.5 14.2 20.2 12.2

68.5 63.7 -7.0 14.2 18.4 29.6

68.5 66.6 -2.8 14.2 19.7 38.7

68.5 67.0 -2.2 14.2 15.5 9.1

“Different from control.

Amino-acid composition of the diets The amino-acid composition of the four diets is presented in Table 12. There are no great differences in the amounts of each amino acid. There is no lack of any of the essential amino acids and all of them are present in greater amounts than the established minimum for fish diets (Hashimoto et al., 1972; Halver, 1976; NRC, 1977). Fatty acids The nature of the fatty acids of one of the components of the silage is indicated in Table 13. It is important to notice the great percentage of fatty acids of the w-3 series (C22). Carcass analysis Table 14 shows the results of carcass analysis for crude protein and fat composition. As expected, the total amount of lipids is higher in the animals at the end of the experiment. Nevertheless, there are differences in the amount of lipids in the carcass of the eels given different feeds; those receiving silage had a greater amount of fat. DISCUSSION

The utilization of silage from non-economic fish or fish offal as a source of protein has been justified for salmonids (Hardy et al., 1984; Jackson et al., 1984; Asgard and Austreng, 1984; Austreng and Asgard, 1986). For eel, the utilization of 40% silage in a ration without previous neutralization (pH = 5.2 ) gave no satisfactory results: eels lost appetite and weight (Affandi, 1985). The present results obtained with diets incorporating fish silage and with pH corrected to that of the control diet (pH=6.3) show greater diet attractiveness and better growth performances than the control, and much better than the commercial diet tested. The growth efficiency for the diets incorpo-

144

rating three different percentages (10,X and 20% ) of protein from fish silage was very similar. The growth efficiency and the food conversion rates for these diets were better than the control (prepared with protein from fish and meat meal). Furthermore, the percent of ingestion was much better for the diets with silage incorporation, indicating.the existence of greater difficulties in the preparation of the control diet. Due to the feeding behaviour of the eels and to the withdrawal of feed particles by the expired water, part of the food is lost (Kuhlmann, 1974). The results (Table 8) show a loss of 11.1% to 20.1% in the diets with silage and of 31.2% in the control, indicating a better binding of the diets incorporating silage. The figures, however, lie in the same order of magnitude as those found by Jurgensen and Nielsen, 1982 (between l/6 and l/3) and Gibrat et al., 1985 (16.6 to 31.8%) in elvers fed different diets. Therefore, the better results obtained with diets containing silage are partially dependent on a greater amount of food actually being ingested by each animal. Even so, the incorporation of silage at lo-20% in the diet increases the growth rate, the food conversion efficiency, the protein efficiency ratio and also the amount of lipid incorporation in the body of eels. The growth rates measured (about 0.3% per day with the control diet and 0.37-0.39% per day with the diets incorporating silage) are in the same order of magnitude as those found by Vassal and Brusle (1984) working with eels of 20 g fed 2% body weight a day of liver paste (growth rate, 0.38%) or a commercial diet (growth rate, 0.30% ) and cultured in cages supplied with water of low salinity (1.2-1.6% ) and median temperature (17”-18.5’ C). Results obtained by Gibrat et al. (1985) working with eels (0.33 to 79 g median weight) in fresh water (25°C) are higher (1.18%-1.71%), but the animals were fed 4.5% wet weight per day of a diet isoproteic (49.2% protein) but hyperenergetic (17.05% fat and 5.703 kcal/g dry weight or 23.86 kJ/g). The food conversion efficiency for the different diets tested (6.1-8.87 ) was identical to those found by Vassal and Brusld (1984) (6-7.8 with liver food and 4.5-6.9 with an artificial diet) and Gibrat et al. (1985) (2.13-7.46 or 5.5610.88 after correction for the percent of food ingestion). The protein efficiency ratios (0.11-0.34 ) are similar to than those found by Vassal and Brush! (0.250.33 and 0.85-1.21% ). In view of the other results, it is difficult to accept the data of the digestibility tests (31.1%-41.9% ), about half of the expected values. Schmitz et al. (1984) found up to 78% in eels between 170 and 230 g, fed with artificial diets administered in gelatin capsules, and Gibrat et al. (1985) found 52.4-80.8% in glass eels fed with a natural and an artificial diet. A technical problem deriving from the low amount of faeces collected is probably at the origin of our unexpected results. The reason for the better growth performances obtained with fish silage diets is not related to the composition of the amino acids of the proteins, but prob-

145

ably to the presence of some food attractants to the eels, either the known mixtures of L amino acids (Mackie and Mitchell, 1983) or the better quality fatty acids present. In fact, one of the main components of the silage used has an excellent lipid composition for fish growth (high percentage of polyunsaturated C22 o-3 series). It is well known that polyunsaturated and longerchain fatty acids of the C22 or C24 o-3 series are required for maximum growth and diet utilization in fish (Lee and Sinnhuber, 1972 ). Another factor that can possibly explain the reported results is the presence of large amounts of sodium in the diets with silage incorporation (the acid is neutralized by NaOH). It will be necessary in future to test the effect of sodium on the intestinal absorption of the components of the diet, in order to evaluate the role played by this mineral in the results obtained. ACKNOWLEDGEMENTS

This work was supported by a NATO grant from the “Science for Stability” Program, project NATO-PO Fishes. The authors are indebted to Dr. Orlando Luis for help with the fatty acid analysis.

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