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Digestibility of low-cost ingredients in pelleted feed by grass carp (Ctenopharyngodon idella C. et V.)
Aquaculture, 51 (1986) 97-103 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
97
DIGESTIBILITY OF LOW-COST INGREDIENTS IN PELLETED FEED BY GRASS CARP (CTENOPHAR YNGODON IDELLA C. et V.)
A.T. LAW Faculty of Fisheries and Marine Science, (Malaysia) (Accepted
Uniuersiti Pertanian Malaysia, Serdang, Sehngor
3 October 1985)
ABSTRACT Law, A.T., 1986. Digestibility of low-cost ingredients in pelleted (Ctenopharyngodon idelIa C. et V.). Aquaculture, 51: 97-103.
feed by grass carp
The digestion coefficients of nutrients in 37% protein MARDI feed as well as in napier and carpet grass meaIs were evaluated in grass carp. Cr,O, was used as an internal marker for the evaluation of digestibility. In the MARDI feed, the fish meal and soya bean meal were digested most by the fish: the digestion coefficients for protein were 90.81% and 96.21%, respectively; for fat the values were 100% and 98.79%, respectively; and for gross energy the values were 83.37% and 82.71%, respectively. These results indicate that it may be feasible to replace fish meal partially with soya bean meal in the MARDI feed for grass carp. The digestion coefficients for dry matter and carbohydrate of maize were 64.76% and 87.85%, respectively, although protein, fat and gross energy in maize were poorly utilized by the fish. Copra cake and rice bran were poorly digested by the fish. These two ingredients should be deleted in feed formulations for this fish. The digestion coefficients of nutrients in napier and carpet grass meals were much higher than those of maize, copra cake and rice bran in the fish, which suggests that grass meals may possibly be used as ingredients in feed formulation for grass carp.
INTRODUCTION
The culturing of grass carp, Ctenopharyngodon idella (C. et V.), has been given top priority by the Government of Malaysia (Pathansali and Zainol, 1976; Ong, 1983). Information on the digestibility of various feeds and locally available grasses and vegetables by this fish is limited and scattered except for studies of the digestibility of guinea grass, Panicum maximum (Hickling, 1966), napier grass, Pennisetum purpureum (Law, 1978), and carpet grass, Axonopus compressus (Law and Syed RazIan, 1981). Previous studies have indicated that the apparent digestibilities of the locally available grasses were very low in this fish; less than 20% dry matter (Law, 1978; Law and Syed Razlan, 1981). This low digestibility of grasses was attributed to the poor grinding mechanism of the alimentary system of this 0044-8486/86/$03.50
0 1986 Elsevier Science Publishers B.V.
1
of
4409.5 k33.6 1.102 0.03 60.86
57.08
Carbohydrate (%)
0.51 0.03 0.03
4203.7 +33.8 2.81i- 0.13 -
59.94
20.45i 3.68* 15.93*
Feces 0.17 0.12 0.01
4609 i- 54.3 l.lO+ 0.03 44.16
49.43
34.54+ 6.15* 9.88*
0.29 0.05 0.28
3980 * 12.5 1.972 0.01 -
69.93
13.50+ 0.97+ 15.602
Feces
3397.7 *28.5 2.78-+ 0.02 -
49.28
0.08 0.05 0.33
0.78 0.12 0.07
4428.9 f 34.3 1.162 0.01 42.86
53.46
29.07* 3.57* 13.272
Feed
0.16 0.05 0.10
3672.6 128.5 2.03-c 0.13 -
65.74
10.22+ 1.28+ 22.74+
Feces 0.02 0.09 0.05
3835.3 k17.3 3.32? 0.13 -
63.56
15.76r l.Ol+ 19.67+
Feces
Ref. diet + rice bran
4497.8 k37.6 1.13-+ 0.03 65.96
44.64
42.7 * 0.56 2.67? 0.12 9.99i 0.04
Feed
Ref. diet + soya bean meal
in grass carp
18.11+ 0.96* 31.35+
Feces
Feed
30.51+ 3.93* 8.48i
aMean 2 S.D.
0.29 0.02 0.08
4493.2 227.2 1.06+ 0.01 61.87
33.4
49.49i 3.502 13.61?
Feed
Feed 1.28 0.11 0.27
feces
Ref. diet + fish meal
and the resulting
cake
3705.3 k41.9 2.45k 0.23 -
61.6
0.46 0.16 0.10
diets,
Ref. diet + copra
Protein (%) Fat (%) Ash (%)
Gross energy (Cal/g) Cr,G, (%) Dry matter (%)
test
15.35* 1.38i 21.675
Feces
diet
diet,
Ref. diet + maize meal
4440.5 i47.8 1.0 i 0.01 59.18
46.94
(%) Gross energy (Cal/g) Cr,C, (%) Dry matter (%)
0.35a 0.04 0.05
Reference
reference
38.32i 3.15+ 11.59+
Feed
MARDI
analyses
Protein (%) Fat (%) Ash (%) Carbohydrate
Proximate
TABLE
99
fish, although once the cell wall of the grass was ruptured, grass carp had a very high ability to absorb the released soluble protein (Law, 1978). This information indicates that the growth rate of grass carp could be increased if the fish were provided with a nutrient-balanced pelleted feed instead of the grasses and leaves of vegetables traditionally used for feeding the fish. A growth study of grass carp fed on a pelleted feed in basins had also indicated that there was a great potential for intensive culture of grass carp using pelleted feed (Huisman and Valentijn, 1981). This preliminary study was undertaken to evaluate the digestibility of low-cost ingredients, including grass meals, in pelleted feed by grass carp. MATERIALS
AND METHODS
Thirty fish with an average weight of 15.3 g were kept in each trial run of the funnel-shaped experimental tank (1.3 m diameter, 0.7 m height) used for the study. There were three runs on each of the test diets and each run lasted 2 to 3 weeks. The description and operation of the experimental tank, the procedures for feeding and feces collection, the analyses of crude protein, fat, ash, dry matter, gross energy and chromic oxide were similar to those described previously (Law, 1984). All analyses were performed in triplicate. Napier or carpet grass meal was prepared as follows: fresh young grass was collected from the University experimental farm, washed with water, dried in an oven at 50°C for one week, and then the dried grass was ground to 2 mm diameter with a feed mill grinder. All test diets were composed of 30% of the test ingredient and 70% of the reference diet, and then 1% of Cr,O, was incorporated as an internal marker. The 37% protein MARDI (Malaysian Agriculture Research and Development Institute) feed was chosen as the reference diet (Law, 1984), while the test ingredients were fish meal, soya bean meal, copra cake, maize meal, rice bran, napier and carpet grass meals. The apparent digestibility of dry matter and nutrients in the diets was evaluated according to Schneider and Flatt (1975). The digestion coefficients of nutrients in the ingredients were estimated according to Cho and Slinger (1979). RESULTS
The proximate analyses of the reference diet, test diets incorporating the MARDI feed, and the resulting feces are shown in Table 1, while the digestion coefficients of the nutrients in the ingredients are summarised in Table 2. The results revealed that both fish meal and soya bean meal were highly digested by this fish. The digestion coefficients of protein, fat, and gross energy for fish meal were 90X%, 100% and 83.37%, respectively,
100 TABLE 2 Digestion coefficients
Dry matter (%) Protein (%) Fat (%) Gross energy (%) Carbohydrate (%) Ash (%)
of nutrients in the ingredients of the MARDI feed for grass carp Fish meal
Soya bean meal
Maize meal
Copra cake
Rice bran
68.13 90.81 100.00 83.37 37.43 nd
81.76 96.21 98.79 82.71 63.37 54.61
64.76 50.61 19.52 55.07 87.85 32.87
9.10 65.35 100.00 18.74 nd nd
4.77 71.11 73.42 21.54 nd nd
nd = not digestible.
TABLE 3 Proximate analyses of grass meal, test diets and the resulting feces in grass carp Ref. diet? + carpet grass meal
Ref. diet + napier grass meal
Feed
Feed
Feces
Protein (W) 33.43 Fat (%) 1.51 Ash (%) 11.10 Carbohydrate (%) 53.96 Gross energy (Cal/g) 4300 Cr,G, (%) 1.03 Dry matter (%) 47.72
* * c
0.24 0.08 0.06
12.11 * 0.88 2 15.56 +
0.34 0.05 0.05
71.45 f 28.7 k 0.03
3884.5 + 39.4 1.97 ?: 0.16 -
35.48 f 2.76 + 11.48 f 50.28
Feces 0.11 0.15 0.11
12.43 f 0.74 * 13.12 + 73.71
4438.0 + 82.6 4182.2 i: 73.1 0.83 + 0.08 1.55 f 0.10 46.45 -
*Proximate analyses of the reference diet are the same as shown in Table 1.
TABLE 4 Digestion coefficients
Dry matter (%) Protein (X) Fat (%) Gross energy (%) Carbohydrate (%) Ash (%) nd = not digestible.
of nutrients in grass meal for grass carp Carpet grass meal
Napier grass meal
20.96 73.37 40.11 22.08 nd 33.73
16.73 75.54 93.84 11.27 nd 74.06
0.39 0.06 0.07
101
while for soya bean, the values were 96.21%, 98.79% and 82.71%, respectively. The nutritive value of maize meal was lower than that of the fish meal and soya bean meal. Copra cake and rice bran were poorly digested by this fish. The proximate analyses of the grass meal diets and the digestion coefficients of the nutrients in the grasses are shown in Tables 3 and 4 respectively. For the carpet grass, the digestion coefficients of dry matter, protein, fat and gross energy were 20.96%, 73.37%, 40.11% and 22.08%, respectively, while for napier grass the values were 16.73%, 75.54%, 93.84% and 11.27%, respectively. DISCUSSION
In Malaysia, grass carp is cultured in earthen ponds and fed with the locally available leaves and grasses such as banana and tapioca leaves, napier and guinea grasses. It takes about 8 months for the fish to grow to a weight of about 2 kg (Hickling, 1960). Previous studies have indicated that grasses were poorly digested in grass carp (Law, 1978; Law and Syed Razlan, 1981); the apparent digestibility of dry matter and protein of napier and carpet grasses were below 20% and 63%, respectively. In order to meet its nutritional requirement, the fish consumes large amounts of grasses. Most probably, the fish is underfed, which results in a slower growth rate than may be possible. In this study, the apparent digestibility of dry matter of the MARDI feed in the fish was 59.18%, 3 to 4 times higher than that of napier (Law, 1978) and carpet grasses (Law and Syed Razlan, 1981). Similarly, the digestion coefficients of the protein and fat of the MARDI feed were much higher than those of the grasses. These data suggest that a faster growth rate and a shorter time to harvest may be expected if the fish were fed with a nutrient-balanced pelleted diet instead of grasses and vegetables, as supported by a preliminary growth study of this fish in tanks. The growth rate of grass carp given MARDI feed was much faster than that of fish fed on carpet grass, the daily weight gains being 1.3% and 0.3%, respectively. Owing to the shortage and high cost of fish meal, aquaculturists have been trying to replace fish meal in their feed formulation by locally available cheap ingredients (Anwar et al., 1982; Davis and Stickney, 1978; IDRC, 1983; Law et al., 1983; Viola and Arieli, 1983; Viola et al., 1982). Viola et al. (1982) successfully replaced fish meal by soya bean meal for the intensive culture of common carp. Davis and Stickney (1978) found that soya bean meal can be used for replacement of fish meal in the culturing of tilapia. However, for grass carp growing in aquaria, neither fish meal nor soya bean meal could be considered as a satisfactory major ingredient for the diet (Dabrowski and Kozak, 1979). Furthermore, grass carp fry fed with soya bean supplemented diets, which had the same protein level together with the same amino acid increment, showed growth retardation.
This reveals that more nutritional research is required for the proper feed formulation for grass carp. In this study, the results indicated that nutrients in both fish meal and soya bean meal were digested equally well by grass carp. Thus it may be feasible to replace a certain amount of fish meal in the MARDI feed with soya bean meal in order to reduce the cost of the feed. However, further experiments are required in this respect, especially in the growth response of the fish fed with pelleted diets under culture pond conditions. Law (1984) reported that jelawat, Leptobarbus hoeuenii (Bleeker), could digest nutrients in copra cake better than soya bean and maize meals. The dry matter digestion coefficient of copra cake in jelawat was 72.28%, while in grass carp it was only 9.10%. The dry matter digestion coefficient of rice bran by grass carp was also very poor, 4.77% as compared to 51.71% in jelawat. Since both copra cake and rice bran were poorly digested by grass carp, they should be replaced by other more useful ingredients in feed formulation for this species. The dry matter and carbohydrate digestion coefficients of maize meal in the fish were 64.76% and 87.85% respectively, while for other nutrients the digestion coefficients were lower than in all other ingredients used in this study. These results indicate that maize meal could be a good source of carbohydrate and energy for grass carp. In the evaluation of the digestibility of fresh young grasses by grass carp, Law and Syed Razlan (1981) reported that the digestion coefficients of dry matter and protein of carpet grass were 20.92% and 62.98% respectively, while for napier grass, the corresponding values were 16.73% and 75.54%, respectively (Law, 1978). In this study, the digestion coefficients of dry matter and protein of the carpet grass meal (dry) and napier grass meal (dry) were not significantly different from the values reported earlier by Law and Syed Razlan (1981) and Law (1978). Thus, grass carp could digest fresh grass and dry grass meal equally, and even when the grass was dried and ground, digestibility by the fish did not improve. However, the digestion coefficients of the dry matter, protein, fat and gross energy of carpet and napier grass meals were much higher than those found in maize, copra cake and rice bran. This finding indicates that grass meal can be used as an ingredient in feed formulation for the intensive culture of grass carp, which would lower the cost of the feed. ACKNOWLEDGEMENTS
The author would like to thank the former head of the Freshwater Fisheries Research Station, MARDI, Melaka, Encik Ahmad Tajuddin bin Zainuddin and his research officer Encik S. Pathmasothy for their cooperation in providing the pelleted feed. The author also wishes to thank Dr. Ang Kok Jee and Dr. Ian G. Anderson for their comments and discussion, Encik Poh Yong Thong, Azahar bin Othman and Zainal Abidin bin Bahari for their technical help, and Puan Badariah Mohd. Yusof for her typing of the manuscript. This project was funded by IDRC/MARDI.
103 REFERENCES Anwar, A., Ishak, M.M., El-Zeiny, M. and Hassanen, G.D.I., 1982. Activated sewage sludge as a replacement for bran-cotton seed meal mixture for carp, Cyprinus curpio L. Aquaculture, 28: 321-325. Cho, C.Y. and Slinger, S.J., 1979. Apparent digestibility measurements in feed stuffs for rainbow trout. In: World Symposium on Finfish Nutrition and Fishfeed Technology. Hamburg, 20-23 June 1978, Vol. Il. Heenemann, Berlin, pp. 239-247. Dabrowski, K. and Kozak, B., 1979. The use of fish meal and soyabean meal as a protein source in the diet of grass carp fry. Aquaculture, 18: 107-114. Davis, A.T. and Stickney, R.R., 1978. Growth responses of Tilapia aurea to dietary protein quality and quantity. Trans. Am. Fish Sot., 107(3): 479-483. Hickling, C.F., 1960. Observations on the growth-rate of the Chinese grass carp, Ctenopharyngodon idellus C. et V. Malay. Agric. J., 43: 49-53. Hickling, C.F., 1966. On the feeding process in the white amur, Ctenopharyngodon idella. J. Zool., 148: 408-419. Huisman, E.A. and Valentijn, P., 1981. Conversion efficiencies in grass carp (Ctenopharyngodon idella, Val.) using a feed for commercial production. Aquaculture, 22: 279-288. IDRC, 1983. Workshop on Asian Finfish Nutrition. 23-26 August 1983. Singapore. Law, A.T., 1978. Digestibility of napier grass (Pennisetum purpureum) in grass carp (Ctenopharyngodon idella). Pertanika, l(1): 51-54. Law, A-T., 1984. Nutritional study of jelawat, Leptobarbus hoeuenii (Bleeker), fed on pelleted feed. Aquaculture, 41: 227-233. Law, A.T. and Syed Razlan b. Syed Putra Jamalullail, 1981. Digestibility of carpet grass (Axonopus compressus) in grass carp (Ctenopharyngodon idella). Pertanika, 4( 1): 91--93. Law, A.T., Cheah, S.H. and Ang, K.J., 1983. An evaluation of the apparent digestibility of some locally available plants and a pelleted feed in three finfishes in Malaysia. Preprint IDRC Workshop on Asian Finfish Nutrition, 23-26 August 1983. Singapore. Ong Kah Sin, 1983. Development and management of aquaculture in Malaysia. Preprint: International Conference on Development and Management of Tropical Living Aquatic Resources. 2-5 August 1983. Universiti Pertanian Malaysia, Serdang, Selangor, Malaysia. Pathansali, D. and Zainol, S., 1976. National plan for development of Aquaculture in Malaysia. In: Aquaculture Planning in Asia, Report of the Regional Workshop in Aquaculture Planning in Asia, Bangkok, Thailand, l-17 October 1975. ADCP/Rep/76/2. Schneider, B.H. and Flatt, W.P., 1975. The Evaluation of Feeds through Digestibility Experiments. Univ. Georgia Press, Athens, GA, 423 pp. Viola, S. and Arieli, Y., 1983. Evaluation of different grains as basic ingredients in complete feeds for carp and tilapia in intensive culture. Bamidgeh 35(2): 38-43. Viola, S., Mokady, S., Rappaport, U. and Arieli, Y., 1982. Partial and complete replacement of fishmeal by soybean meal in feeds for intensive culture of carp. Aquaculture, 26: 223-236.
97
DIGESTIBILITY OF LOW-COST INGREDIENTS IN PELLETED FEED BY GRASS CARP (CTENOPHAR YNGODON IDELLA C. et V.)
A.T. LAW Faculty of Fisheries and Marine Science, (Malaysia) (Accepted
Uniuersiti Pertanian Malaysia, Serdang, Sehngor
3 October 1985)
ABSTRACT Law, A.T., 1986. Digestibility of low-cost ingredients in pelleted (Ctenopharyngodon idelIa C. et V.). Aquaculture, 51: 97-103.
feed by grass carp
The digestion coefficients of nutrients in 37% protein MARDI feed as well as in napier and carpet grass meaIs were evaluated in grass carp. Cr,O, was used as an internal marker for the evaluation of digestibility. In the MARDI feed, the fish meal and soya bean meal were digested most by the fish: the digestion coefficients for protein were 90.81% and 96.21%, respectively; for fat the values were 100% and 98.79%, respectively; and for gross energy the values were 83.37% and 82.71%, respectively. These results indicate that it may be feasible to replace fish meal partially with soya bean meal in the MARDI feed for grass carp. The digestion coefficients for dry matter and carbohydrate of maize were 64.76% and 87.85%, respectively, although protein, fat and gross energy in maize were poorly utilized by the fish. Copra cake and rice bran were poorly digested by the fish. These two ingredients should be deleted in feed formulations for this fish. The digestion coefficients of nutrients in napier and carpet grass meals were much higher than those of maize, copra cake and rice bran in the fish, which suggests that grass meals may possibly be used as ingredients in feed formulation for grass carp.
INTRODUCTION
The culturing of grass carp, Ctenopharyngodon idella (C. et V.), has been given top priority by the Government of Malaysia (Pathansali and Zainol, 1976; Ong, 1983). Information on the digestibility of various feeds and locally available grasses and vegetables by this fish is limited and scattered except for studies of the digestibility of guinea grass, Panicum maximum (Hickling, 1966), napier grass, Pennisetum purpureum (Law, 1978), and carpet grass, Axonopus compressus (Law and Syed RazIan, 1981). Previous studies have indicated that the apparent digestibilities of the locally available grasses were very low in this fish; less than 20% dry matter (Law, 1978; Law and Syed Razlan, 1981). This low digestibility of grasses was attributed to the poor grinding mechanism of the alimentary system of this 0044-8486/86/$03.50
0 1986 Elsevier Science Publishers B.V.
1
of
4409.5 k33.6 1.102 0.03 60.86
57.08
Carbohydrate (%)
0.51 0.03 0.03
4203.7 +33.8 2.81i- 0.13 -
59.94
20.45i 3.68* 15.93*
Feces 0.17 0.12 0.01
4609 i- 54.3 l.lO+ 0.03 44.16
49.43
34.54+ 6.15* 9.88*
0.29 0.05 0.28
3980 * 12.5 1.972 0.01 -
69.93
13.50+ 0.97+ 15.602
Feces
3397.7 *28.5 2.78-+ 0.02 -
49.28
0.08 0.05 0.33
0.78 0.12 0.07
4428.9 f 34.3 1.162 0.01 42.86
53.46
29.07* 3.57* 13.272
Feed
0.16 0.05 0.10
3672.6 128.5 2.03-c 0.13 -
65.74
10.22+ 1.28+ 22.74+
Feces 0.02 0.09 0.05
3835.3 k17.3 3.32? 0.13 -
63.56
15.76r l.Ol+ 19.67+
Feces
Ref. diet + rice bran
4497.8 k37.6 1.13-+ 0.03 65.96
44.64
42.7 * 0.56 2.67? 0.12 9.99i 0.04
Feed
Ref. diet + soya bean meal
in grass carp
18.11+ 0.96* 31.35+
Feces
Feed
30.51+ 3.93* 8.48i
aMean 2 S.D.
0.29 0.02 0.08
4493.2 227.2 1.06+ 0.01 61.87
33.4
49.49i 3.502 13.61?
Feed
Feed 1.28 0.11 0.27
feces
Ref. diet + fish meal
and the resulting
cake
3705.3 k41.9 2.45k 0.23 -
61.6
0.46 0.16 0.10
diets,
Ref. diet + copra
Protein (%) Fat (%) Ash (%)
Gross energy (Cal/g) Cr,G, (%) Dry matter (%)
test
15.35* 1.38i 21.675
Feces
diet
diet,
Ref. diet + maize meal
4440.5 i47.8 1.0 i 0.01 59.18
46.94
(%) Gross energy (Cal/g) Cr,C, (%) Dry matter (%)
0.35a 0.04 0.05
Reference
reference
38.32i 3.15+ 11.59+
Feed
MARDI
analyses
Protein (%) Fat (%) Ash (%) Carbohydrate
Proximate
TABLE
99
fish, although once the cell wall of the grass was ruptured, grass carp had a very high ability to absorb the released soluble protein (Law, 1978). This information indicates that the growth rate of grass carp could be increased if the fish were provided with a nutrient-balanced pelleted feed instead of the grasses and leaves of vegetables traditionally used for feeding the fish. A growth study of grass carp fed on a pelleted feed in basins had also indicated that there was a great potential for intensive culture of grass carp using pelleted feed (Huisman and Valentijn, 1981). This preliminary study was undertaken to evaluate the digestibility of low-cost ingredients, including grass meals, in pelleted feed by grass carp. MATERIALS
AND METHODS
Thirty fish with an average weight of 15.3 g were kept in each trial run of the funnel-shaped experimental tank (1.3 m diameter, 0.7 m height) used for the study. There were three runs on each of the test diets and each run lasted 2 to 3 weeks. The description and operation of the experimental tank, the procedures for feeding and feces collection, the analyses of crude protein, fat, ash, dry matter, gross energy and chromic oxide were similar to those described previously (Law, 1984). All analyses were performed in triplicate. Napier or carpet grass meal was prepared as follows: fresh young grass was collected from the University experimental farm, washed with water, dried in an oven at 50°C for one week, and then the dried grass was ground to 2 mm diameter with a feed mill grinder. All test diets were composed of 30% of the test ingredient and 70% of the reference diet, and then 1% of Cr,O, was incorporated as an internal marker. The 37% protein MARDI (Malaysian Agriculture Research and Development Institute) feed was chosen as the reference diet (Law, 1984), while the test ingredients were fish meal, soya bean meal, copra cake, maize meal, rice bran, napier and carpet grass meals. The apparent digestibility of dry matter and nutrients in the diets was evaluated according to Schneider and Flatt (1975). The digestion coefficients of nutrients in the ingredients were estimated according to Cho and Slinger (1979). RESULTS
The proximate analyses of the reference diet, test diets incorporating the MARDI feed, and the resulting feces are shown in Table 1, while the digestion coefficients of the nutrients in the ingredients are summarised in Table 2. The results revealed that both fish meal and soya bean meal were highly digested by this fish. The digestion coefficients of protein, fat, and gross energy for fish meal were 90X%, 100% and 83.37%, respectively,
100 TABLE 2 Digestion coefficients
Dry matter (%) Protein (%) Fat (%) Gross energy (%) Carbohydrate (%) Ash (%)
of nutrients in the ingredients of the MARDI feed for grass carp Fish meal
Soya bean meal
Maize meal
Copra cake
Rice bran
68.13 90.81 100.00 83.37 37.43 nd
81.76 96.21 98.79 82.71 63.37 54.61
64.76 50.61 19.52 55.07 87.85 32.87
9.10 65.35 100.00 18.74 nd nd
4.77 71.11 73.42 21.54 nd nd
nd = not digestible.
TABLE 3 Proximate analyses of grass meal, test diets and the resulting feces in grass carp Ref. diet? + carpet grass meal
Ref. diet + napier grass meal
Feed
Feed
Feces
Protein (W) 33.43 Fat (%) 1.51 Ash (%) 11.10 Carbohydrate (%) 53.96 Gross energy (Cal/g) 4300 Cr,G, (%) 1.03 Dry matter (%) 47.72
* * c
0.24 0.08 0.06
12.11 * 0.88 2 15.56 +
0.34 0.05 0.05
71.45 f 28.7 k 0.03
3884.5 + 39.4 1.97 ?: 0.16 -
35.48 f 2.76 + 11.48 f 50.28
Feces 0.11 0.15 0.11
12.43 f 0.74 * 13.12 + 73.71
4438.0 + 82.6 4182.2 i: 73.1 0.83 + 0.08 1.55 f 0.10 46.45 -
*Proximate analyses of the reference diet are the same as shown in Table 1.
TABLE 4 Digestion coefficients
Dry matter (%) Protein (X) Fat (%) Gross energy (%) Carbohydrate (%) Ash (%) nd = not digestible.
of nutrients in grass meal for grass carp Carpet grass meal
Napier grass meal
20.96 73.37 40.11 22.08 nd 33.73
16.73 75.54 93.84 11.27 nd 74.06
0.39 0.06 0.07
101
while for soya bean, the values were 96.21%, 98.79% and 82.71%, respectively. The nutritive value of maize meal was lower than that of the fish meal and soya bean meal. Copra cake and rice bran were poorly digested by this fish. The proximate analyses of the grass meal diets and the digestion coefficients of the nutrients in the grasses are shown in Tables 3 and 4 respectively. For the carpet grass, the digestion coefficients of dry matter, protein, fat and gross energy were 20.96%, 73.37%, 40.11% and 22.08%, respectively, while for napier grass the values were 16.73%, 75.54%, 93.84% and 11.27%, respectively. DISCUSSION
In Malaysia, grass carp is cultured in earthen ponds and fed with the locally available leaves and grasses such as banana and tapioca leaves, napier and guinea grasses. It takes about 8 months for the fish to grow to a weight of about 2 kg (Hickling, 1960). Previous studies have indicated that grasses were poorly digested in grass carp (Law, 1978; Law and Syed Razlan, 1981); the apparent digestibility of dry matter and protein of napier and carpet grasses were below 20% and 63%, respectively. In order to meet its nutritional requirement, the fish consumes large amounts of grasses. Most probably, the fish is underfed, which results in a slower growth rate than may be possible. In this study, the apparent digestibility of dry matter of the MARDI feed in the fish was 59.18%, 3 to 4 times higher than that of napier (Law, 1978) and carpet grasses (Law and Syed Razlan, 1981). Similarly, the digestion coefficients of the protein and fat of the MARDI feed were much higher than those of the grasses. These data suggest that a faster growth rate and a shorter time to harvest may be expected if the fish were fed with a nutrient-balanced pelleted diet instead of grasses and vegetables, as supported by a preliminary growth study of this fish in tanks. The growth rate of grass carp given MARDI feed was much faster than that of fish fed on carpet grass, the daily weight gains being 1.3% and 0.3%, respectively. Owing to the shortage and high cost of fish meal, aquaculturists have been trying to replace fish meal in their feed formulation by locally available cheap ingredients (Anwar et al., 1982; Davis and Stickney, 1978; IDRC, 1983; Law et al., 1983; Viola and Arieli, 1983; Viola et al., 1982). Viola et al. (1982) successfully replaced fish meal by soya bean meal for the intensive culture of common carp. Davis and Stickney (1978) found that soya bean meal can be used for replacement of fish meal in the culturing of tilapia. However, for grass carp growing in aquaria, neither fish meal nor soya bean meal could be considered as a satisfactory major ingredient for the diet (Dabrowski and Kozak, 1979). Furthermore, grass carp fry fed with soya bean supplemented diets, which had the same protein level together with the same amino acid increment, showed growth retardation.
This reveals that more nutritional research is required for the proper feed formulation for grass carp. In this study, the results indicated that nutrients in both fish meal and soya bean meal were digested equally well by grass carp. Thus it may be feasible to replace a certain amount of fish meal in the MARDI feed with soya bean meal in order to reduce the cost of the feed. However, further experiments are required in this respect, especially in the growth response of the fish fed with pelleted diets under culture pond conditions. Law (1984) reported that jelawat, Leptobarbus hoeuenii (Bleeker), could digest nutrients in copra cake better than soya bean and maize meals. The dry matter digestion coefficient of copra cake in jelawat was 72.28%, while in grass carp it was only 9.10%. The dry matter digestion coefficient of rice bran by grass carp was also very poor, 4.77% as compared to 51.71% in jelawat. Since both copra cake and rice bran were poorly digested by grass carp, they should be replaced by other more useful ingredients in feed formulation for this species. The dry matter and carbohydrate digestion coefficients of maize meal in the fish were 64.76% and 87.85% respectively, while for other nutrients the digestion coefficients were lower than in all other ingredients used in this study. These results indicate that maize meal could be a good source of carbohydrate and energy for grass carp. In the evaluation of the digestibility of fresh young grasses by grass carp, Law and Syed Razlan (1981) reported that the digestion coefficients of dry matter and protein of carpet grass were 20.92% and 62.98% respectively, while for napier grass, the corresponding values were 16.73% and 75.54%, respectively (Law, 1978). In this study, the digestion coefficients of dry matter and protein of the carpet grass meal (dry) and napier grass meal (dry) were not significantly different from the values reported earlier by Law and Syed Razlan (1981) and Law (1978). Thus, grass carp could digest fresh grass and dry grass meal equally, and even when the grass was dried and ground, digestibility by the fish did not improve. However, the digestion coefficients of the dry matter, protein, fat and gross energy of carpet and napier grass meals were much higher than those found in maize, copra cake and rice bran. This finding indicates that grass meal can be used as an ingredient in feed formulation for the intensive culture of grass carp, which would lower the cost of the feed. ACKNOWLEDGEMENTS
The author would like to thank the former head of the Freshwater Fisheries Research Station, MARDI, Melaka, Encik Ahmad Tajuddin bin Zainuddin and his research officer Encik S. Pathmasothy for their cooperation in providing the pelleted feed. The author also wishes to thank Dr. Ang Kok Jee and Dr. Ian G. Anderson for their comments and discussion, Encik Poh Yong Thong, Azahar bin Othman and Zainal Abidin bin Bahari for their technical help, and Puan Badariah Mohd. Yusof for her typing of the manuscript. This project was funded by IDRC/MARDI.
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