APPARENT DIGESTIBILITY OF SELECTED FEED INGREDIENTS IN DIETS FOR MUD CRAB ( Scylla paramamosain )

Cultured mud crabs (Scylla spp.) are commonly fed with ‘trash’ fish. Insufficient supply, high cost and variable quality of ‘trash’ fish has lead to a need to develop costeffective and environmentally friendly formulated diets. This study was conducted to determine quality of selected feed ingredients as protein sources in mud crab diets based on their nutrient composition and digestibility coefficients for dry matter (ADMD), crude protein, lipid and energy. The digestibility coefficients for ADMD ranged from 82.46% to 89.20%. Animal-based feedstuffs such as shrimp head, tiny shrimp and squid liver meal had higher ADMD values than fish meal. Of the plant-based feedstuffs, soy bean meal had the highest ADMD values (89.20%) and corn gluten had the lowest (82.46%). Corn gluten had the lowest protein digestibility (78.81%) and soy bean meal had the highest (96.05%). The lowest energy digestibility (71.13%) was obtained in corn gluten meal. Soy bean meal had a higher energy digestibility value (98.48%) than fish meal (85.95%). All animal meal sources had similar energy digestibility values (85.86%—92.09%).

value unless it can be digested and absorbed by the targe t spe cie s.Co nse que ntly, knowledge of nutrient digestibility of various feed ingredients used in formulating diets for the target species is important.Lee & Lawrence (1997) recommended the use of chromic oxide (Cr 2 O 3 ) as an inert indicator to measure dige stibility o f fe e d ingre dients fo r crustaceans and many researchers have reported the apparent digestibility of dry matter, protein, lipid, carbohydrate using Cr 2 O 3 (Forster & Gabbott, 1971;Fennuci et al., 1982;Akiyama et al., 1989;Tuan et al., 2006;Catacutan et al., 2003).
Digestibility studies of some ingredients by Scylla serrata have been reported by Tuan et al. (2006) and Catacutan et al. (2003).These results indicated that S.serrata can efficiently utilize certain feed ingredients.Apparent dry matter digestibility of both studies was 85.2%-93.6%(Catacutan et al., 2003) and 70.0%-95.7%(Tuan et al., 2006).This information is not yet

INTRODUCTION
Mud crab has good potential for commercial culture.Cultured mud crabs are commonly fed with 'trash' fish.Ho weve r, due to the insufficient supply, variable cost and quality of 'trash' fish, there is a need to develop coste ffe ctive and enviro nmentally frie ndly formulated diets.Cost effective feed can be produced thro ugh the fo rmulatio n o f inexpensive feed ingredients and inclusion of ingredients with high digestibility which is beneficial for the environment.Some potential ingredients available for formulated crab diets are: fish, squid liver, tiny shrimp, shrimp head, corn gluten, and soy bean meal.Effective incorporation of an ingredient, however, requires information on its digestibility by the target species.
A feed ingredient may appear from its chemical composition to be an excellent source of nutrients but may have little actual available for Scylla paramamosain.This study was conducted to determine the suitability of selected feed ingredients as protein sources for S. paramamosain diets based on their nutrient composition and the digestibility coefficients for dry matter, crude protein, lipid and energy.

MATERIAL AND METHODS
A total of 48 mud crabs (mean body weight 120.5 ± 7.1 gram) were used to test the suitability of the following test ingredients for inclusion in mud crab diets: local fish meal, shrimp head meal, tiny shrimp meal, squid liver meal, corn gluten meal, defatted soybean meal, and feather meal.
The methods of Cho et al. (1982) and Forster (1999) were adapted for this study and used a ratio of 70:30 of the reference diet to test ingredient (Table 1).The reference diet was formulated to meet known nutrient requirements of mud crabs.All experimental diets contained 1% Cr 2 O 3 as an external indicator and 2% carboxymethylcellulose (CMC) as a binder.The mud crabs were acclimated with a reference diet (without Cr 2 O 3 ) fo r 2 we eks afte r which the y we re fed experimental diets twice daily (08.00 h and 15.00 h) at a rate of 5% body weight per day.After acclimation, all mud crabs were assigned to the experimental diets groups.Six crabs were included for each group with triplicates.Faeces were pooled from crabs in each replication until enough was obtained for analysis.All sample s were store d in a refrigerator until required for analysis.The feeds and faeces were analyzed for proximate analysis using standard methods (AOAC, 1990) and for Cr 2 O 3 (Furukawa & Tsukahara, 1966).
Apparent digestibility coefficients (ADCs) of dry matter, protein, energy and lipid were then measured using the methods of Cho et al. (1982) and Forster (1999) with chromic oxide as the inert marker.Apparent digestibility coefficients (ADCs) of each nutrient were calculated from the equation: Where M and N are the percentage of marker and nutrient, respectively, and d and f are diet and faeces, respectively.When ingredients are partially substituted into the reference diet to give a combined diet, the equation for any given nutrient becomes: All data were analyzed by one-way ANOVA and differences between means treatment were considered significant at P<0.05 (Steell & Torrie, 1960).

RESULTS
The proximate composition (g/100 g dry weight) of various feed ingredients is shown in Table 2. Protein levels in fish meal and other feedstuffs of animal origin used in this experiment were generally high (34.69%-86.30%).Protein content of feed ingredients from plant sources ranged from 54.13% to 60.89%.Likewise, the levels of ash in fish meal and shrimp head meal were higher (19.38%-33.42%)than those in feed ingredients of plant origin (1.29%-6.92%).The level of fiber in fish meal was lower than that of other ingredients tested.Squid liver meal had the highest lipid content (17.76%).
Table 3 shows the apparent digestibility coefficients (ADCs) for dry matter (ADMD), protein, lipid, and energy.The digestibility coefficients for ADMD ranged from 82.46% to 89.20%.Of the feedstuffs of animal origin head shrimp, tiny shrimp and squid liver meal had higher ADMD values than fish meal.Soy bean Analysis of variance (Table 3) showed that protein, lipid and energy digestibility values of some ingredients were significantly different from one another (P<0.05).Corn gluten had the lowest protein digestibility value while soy bean meal had the highest (P<0.05).Protein digestibility values of local fish, head shrimp, and squid liver meal were not significantly different from one another (P>0.05).
Lipid digestibility values of squid liver and head shrimp meal were higher than soy bean meal (P<0.05).Lipid digestibility values of local fish, head shrimp, and corn gluten meal were not significantly different from one another (P>0.05).
Energy digestibility values of all ingredients were relatively high (71.13%-98.48%).The lowest energy digestibility value was obtained with corn gluten meal.Soy bean meal had a higher energy digestibility value than fish meal.All animal meal sources had similar energy digestibility values (Table 3).

DISCUSSION
Protein quality of dietary ingredients is generally a leading factor affecting mud crab performance, and protein digestibility is the first measure of its availability by mud crab.Protein quality of dietary protein sources depends on the composition of amino acids and the ir digestibility.Deficiency of an essential amino acid leads to poor utilization of dietary protein and consequently reduces growth and decreases feed efficiency (Halver & Hardy, 2002).The present study showed that ADCs of dry matter, protein, lipid, and energy in the test ingredients for mud crab, S. paramamosain were affe cte d by te st ingredients (P<0.05).The differences in ADCs of nutrients and energy may be explained by differences in chemical composition, origin, and the processing of these feed ingredients (Table 2).
The test ingredients were efficiently utilized by mud crab, S. paramamosain as indicated by the high ADMD values (82.46% to 89.20%).Akiyama et al. (1989) reported in Penaeus vannamei that purified feedstuffs were efficiently digested compared with practical feedstuffs, which ranged from 21.4% to 91.4%.The other result in P. setiferus showed that ADMD tended to decrease as dietary ash content of ingredients increased (Reigh et al., 1990).Soy bean meal protein is considered to be highly digestible to many crustacean species (Catacutan, 1997;Mu et al., 2000).In this study, the ADMD and ACPD of corn gluten were lower than for soy bean meal and similar results have been found for Penaeus setiferus (Brunson et al., 1997).However, the opposite was observed in crayfish, Procambarus clarkii (Reigh et al., 1990) and mud crab, S. serrata (Catacutan et al., 2003).
We therefore suggest that fish, head shrimp, and squid meal are suitable protein sources for mud crabs.Other ingredients, especially of soy bean meal, also appeared to be good dietary protein sources for mud crabs.It is therefore suggested that shrimp head meal and corn gluten meal are suitable dietary lipid sources for mud crabs (Table 3).
Fish meal is one of the most expensive and sought after ingredients for aquaculture diets and has become the most critical ingredient in aquafeed production.Increasing cost and demand of fish meal have encouraged feed manufacturers to se arch fo r che ape r alternative protein source such as plant protein.Fish nutritionists have tried to use less expensive plant protein to partially or totally replace fish meal.However, substitution of fish meal with other ingredients, especially of plant origin, is likely to compromise nutrient balance.Because of the increasing cost of fish meal and do ubts co nce rning its long-te rm availability, much research has been carried out to find an alternative protein source.Tuan et al. (2006) found that soy bean meal gave the highest ADMD (P<0.05) for juvenile mud crabs (S. serrata, Forskal 1775).In another study (Catacutan et al., 2003) showed that soy bean gave lower ADMD than corn meal for juvenile mud crabs (S. serrata).Moreover, protein digestibility for shrimp meal was not significantly different from fish meal (Pe"0.05);nevertheless, it was lower than that of soybean meal.Findings such as these indicate that plantbased nutrient sources can be exploited to substitute fishmeal in formulated diets for mud crabs.In particular, the current findings suggest that soybean meal may be a useful component for fo rmulating diets fo r S. paramamosain.
Based on its digestibility values, it is proposed that soy bean meal is a suitable ingredient to substitute for fish meal in Indonesian Aquaculture Journal Vol.2 No.1, 2007 formulated diets for mud crabs.However, further research is neede d to asses its performance in term of growth and survival of cultured mud crab.

Table 3 .
Digestibility of some feed ingredients on mud crab * Values in the same column followed with similar superscript are not significantly different (P>0.05)