REPLACEMENT OF FISH MEAL PROTEIN BY SOY BEAN AND CORN GLUTEN MEAL PROTEINS IN THE DIET OF MUD CRAB , Scylla paramamosain

Mud crab culture relies heavily on trash fish as the main source of feed ingredients. Artificial diets have been developed for mud crab and most of them have high content of fish meal. The increasing cost and demand of fish meal has encouraged feed manufacture to search for cheaper alternative protein sources such as plant protein. There is an urgent need to find suitable alternative protein sources to reduce the dependence of fish meal in mud crab diet. The objective of this study was to develop compounded feeds for juvenile of mud crab with reduced fish meal content, and as an alternative of trash fish feeding. For that reason, the experiment was done. Experimental diets were fish meal, 20% of soy bean (20% SBP), 40% of soy bean (40% SBP), 20% of corn gluten (20% CGP), and 40% of corn gluten meal protein (40% CGP). Average initial mud crab body weight of 0.65 ± 0.03 g was fed experimental diets for 56 days. The result showed that dietary fish meal protein can be replaced by 20% of soy bean and 20%–40% of corn gluten proteins for mud crab (Scylla paramamosain) diet. Thus, it can arguably be concluded that soy bean and corn gluten proteins are the alternative protein sources to partially replaced fish meal.


INTRODUCTION
Mud crab culture relies heavily on trash fish to feed cultured fish.Artificial diets have been developed for mud crab (Chin et al., 1992).These diets have high content of fish meal, the most common protein source in aquafeeds.With the increasing population and increased fishing pressure, the global production of fish meal has been in a state of decline whilst the demand for aquaculture has been steadily increasing (Tacon, 1996).
Fish meal is readily recognized as the best source of dietary protein and n-3 fatty acid e ico sape ntae no ic acid (EPA) and docosahexaenoic acid (DHA), which are the essential dietary requirement of tropical marine species (King, 2004).Fish meal is also one of the most expensive and demanded ingredients and has become the main and most critical ingredient in aquafeed production.The increasing cost and demand of fish meal has encouraged feed manufacturer to search for cheaper alternative protein sources such as plant protein.Fish nutritionists have tried to use less expensive plant proteins to partially or totally replace fish meal.Substitution with other ingredients, especially from plant origin, is likely to compromise nutrient balance.
Considering the increasing cost of fish meal and doubt concerning its long term availability, many researches have been carried out to find alternative protein sources as fish meal substitutes.Williams et al. (2003) reported that in order aquaculture to make a net contribution to human supplies, the present use of fish meal in aquaculture diets must be substantially reduced.
From market availability and nutritional value, the prime candidates for replacing fish meal in mud crab diet are soy bean meal and corn gluten although the protein content of soy bean meal is less than that of fish meal.
Until present, artificial feed for mud crab has not available yet.In mud crab feed development, it is an urgent issue to find a suitable alternative to reduce fish meal portion in mud crab diet.The objective of this study was to develop compounded feeds for juveniles of mud crab with reduced fish meal content, and serve as alternative feed ingredients to trash fish feeding.

MATERIALS AND METHODS
Mud crab juveniles (crablet) were produced in an oval tank of 5-m 3 volume, after which 120 of mud crab juveniles with the average initial body weight of 0.65 ± 0.03 g were transferred and reared individually using PVC compartments in several 30 L tanks equipped with flow through system and aeration.Eight juveniles of mud crab were reared in each tank.The experiment was arranged in complete randomized design (CRD) with 5 treatments and 3 replications.
Crabs were fed with 5%-10% of body weight twice a day for 9 weeks.All crabs were individually measured body weight every week.All data were analyzed using one-way ANOVA and the differences between means treatment were considered significant at P<0.05 (Steel & Torrie, 1980).

RESULT AND DISCUSSION
The response of mud crab juveniles, in term of average body weight, toward different levels of soy bean and corn gluten proteins containe d in the expe rimental die ts is presentented in Figure 1.The best trend of growth after 2 weeks was shown by crab juveniles fed with the experimental diet of 40% SBP.
The initial average body weight of mud crab was 0.6 gram and gaining weight of 3.52 to 4.98 gram after 56 days.Analysis variance showed that the average weight gain and final body weight were significantly affected by the levels of soy bean and corn gluten proteins in the diets (P<0.05)(Table 2).The increasing level of soy bean protein in the diet reduced weight gain.Mud crab fed on diet of 40% of soy bean protein (40% SBP) had significant lower weight gain than those fed on diet containing fish meal.This result indicates that replacement of fish meal protein by soy bean protein for better growth of mud crab should be less than 40% percent.
Mud crab fed on diet with the replacement of fish meal protein by 20% of soy bean protein (20% SBP), 20% of corn gluten (20%CGP), and 40% of corn gluten protein (40% CGP) had not shown significant different weight gain (P<0.05).Marasigan et al. (1999) reported that mud crab, Scylla serrata and Scylla transquebarica This result indicates that source of protein affected the growth of mud crab.Dietary fish meal protein can be replaced by 20% of soy bean and 20%-40% corn gluten protein in the diet of mud crab (Scylla paramamosain).Thus, it can possibly state that soy bean and corn gluten protein can serve as alternative protein sources to partially subtitute fish meal.
The result of this experiment was supported by analysis of feeding habit of mud crab itself.The mud crab belongs to omnivore group, which feeds on detritus (35.7%), fish (23.6% ), and crustacean (18.3%) (Prasad & Neelakantan, 1988).In other word, mud crab has the ability to use protein from plant sources such as soy bean and corn gluten protein.

CONCLUSSION
Dietary fish meal protein can be replaced by 20% of soy bean and 20%-40% of corn gluten pro te ins fo r mud crab (Scylla paramamosain) die t.This leads to the conclusion that soy bean and corn gluten proteins might serve as potential alternative protein sources to partially or fully subtitute fish meal content in the diet of mud crab.

Figure 1 .
Figure 1.Rate of body weight gain of mud crab juveniles

Table 1 .
Composition of experimental diets

Table 2 .
Initial, final weight, and weight gain of mud crab fed on experimental diets after 56 days Values in the column with the same letter are not significantly different (p>0.05)