Apparent digestibility of selected feedstuffs by mud crab, Scylla serrata

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1 Aquaculture 216 (2003) Apparent digestibility of selected feedstuffs by mud crab, Scylla serrata Mae R. Catacutan a, *, Perla S. Eusebio a, Shin-ichi Teshima b a Aquaculture Department, Southeast Asian Fisheries Development Center, P.O. Box 256, Tigbauan, Iloilo 5021, Philippines b Laboratory of Aquatic Animal Nutrition, Kagoshima University, , Shimoarata, Kagoshima City 890, Japan Received 30 April 2002; received in revised form 6 August 2002; accepted 7 August 2002 Abstract A feeding experiment was conducted to determine apparent digestibility coefficients for dry matter (ADMD), crude protein (ACPD), crude fat (ACFD), crude fiber (ACFbD), nitrogen-free extract or NFE (ANFED), and crude ash (AAD) of selected feed ingredients for mud crab, Scylla serrata. The nine feed ingredients were Peruvian fish meal, squid meal, Acetes sp., meat and bone meal, copra meal, wheat flour, rice bran, corn meal, and defatted soybean meal. A reference diet (RF) and test diets (consisted of 70% RF diet and 30% of the feedstuff) were used with Cr 2 O 3 as external indicator. The ADMD of the RF and test diets were high except for diet with meat and bone meal. Crude protein, crude fiber, and ash of feedstuffs were digestible in mud crab. Nutrients in squid meal, corn meal, and defatted soybean meal were digested well (ACFbD > 95%; ANFED>92%; AAD>71%) compared with nutrients in the meat and bone meal. The AAD of copra meal, wheat flour, rice bran, and meat and bone meal were similar. The ACFD in carbohydrate-rich plant feedstuffs were significantly higher than that in protein-rich animal feedstuffs. For this species, the relative amounts of dietary protein and NFE in feedstuffs had an effect on the ACFD but not on ADMD. D 2003 Elsevier Science B.V. All rights reserved. Keywords: S. serrata; Apparent digestibility; Feedstuffs 1. Introduction The mud crab (Scylla serrata), a popular seafood, is recognized as a potential crustacean species for commercial culture (Williams and Field, 1999). It has been cultured * Corresponding author. Tel.: ; fax: address: mrc@aqd.seafdec.org.ph (M.R. Catacutan) /03/$ - see front matter D 2003 Elsevier Science B.V. All rights reserved. PII: S (02)

2 254 M.R. Catacutan et al. / Aquaculture 216 (2003) with other species as a secondary product, but the growing market is now supplied by production from monoculture system with increased stocking density. Feed is an important component in this system and the traditional feed, which is trash fish, has many disadvantages compared to using formulated feed. In the commercial culture production of mud crab, feeding with formulated diets would be practical and economical. A feed may contain the adequate amount of nutrients formulated for a species but will just be wasted and detrimental to the environment if not efficiently assimilated. An effective feed can be prepared when information on digestibility of nutrients in feedstuffs has been considered in its formulation. There are many factors that may affect measurement of digestibility, but the most crucial is the leaching of nutrients from the feed and fecal matter into the water. In crustaceans, leaching is minimized by using a good feed binder, feed attractant, and by frequent collection of the egesta that is enveloped by a thin membrane. Among the methods in feed digestibility studies in crustaceans, the use of chromic oxide (Cr 2 O 3 ) as an inert indicator is recommended with procedural steps to insure accuracy (Lee and Lawrence, 1997). The apparent digestibility coefficients of dry matter, protein, lipids, and carbohydrate in crustaceans had already been reported using Cr 2 O 3 (Nose, 1964; Lee, 1970; Forster and Gabbott, 1971; Fenucci et al., 1982; Teshima and Kanazawa, 1983; Smith et al., 1985; Akiyama et al., 1989; Catacutan, 1991; Koshio et al., 1992; Deering et al., 1996), but the review on digestibility studies in crustaceans by Lee and Lawrence (1997) had no report on any of the Scylla species. This study determined the apparent digestibility coefficients of nutrients in common aquaculture feedstuffs in the mud crab, S. serrata. 2. Materials and methods Mud crabs, S. serrata (Keenan et al., 1998), from the hatchery of Southeast Asian Fisheries Development Center/Aquaculture Department and grown in ponds were stocked individually in 60 l tanks equipped with aeration and polyvinyl chloride (PVC) substrates. Tanks were filled with seawater (32x) up to 12 cm and allowed to flow through for about 30 min in the morning after cleaning, and in the afternoon before feeding. Apparent digestibility measurement of nutrients in feedstuffs was done using a reference diet (RF) with 1% chromic oxide (Cr 2 O 3 ) as external indicator. A test diet consisted of 70% RF and 30% of the feedstuff to be tested (Peruvian fish meal, squid meal, Acetes sp., meat and bone meal, copra meal, wheat flour, rice bran, corn meal or defatted soybean meal). The estimated metabolizable energy of diets was about 17 MJ/kg (Table 1). Diets contained binders (cooked seaweed of Gracilaria sp., cooked wheat flour, and carboxymethyl cellulose) and were extruded three times to make the diets water stable and prepared according to Catacutan (2002). Crabs (mean body weight or BW, F 7.5 g) were fed RF for 2 weeks and then starved for 2 to 3 days before feeding RF and test diets. Each diet was fed to six crabs (1:1 sex ratio) with two crabs as one replicate. Feed was given once daily in the morning at satiety or about 2% to 2.5% of the body weight. Fecal matter was collected by hand (using a tweezer) after a week of feeding and it was done continuously 3 to 4 h after feeding. Collected fecal matter was rinsed in distilled water and kept in 80 jc before freeze

3 M.R. Catacutan et al. / Aquaculture 216 (2003) Table 1 Composition of the reference (RF) and test diets (%) Ingredients RF diet a Test diet Acetes sp Peruvian fish meal Squid meal 8.00 Defatted soybean meal Seaweed 5.00 Wheat flour Rice bran 8.65 Common Ingredients b 9.85 Reference diet 70 Test ingredient c 30 Total a RF formulation based on Catacutan (2002). b Cr ; soybean lecithin, 0.25; cholesterol, 0.1; dicalcium phosphate, 2; cod liver oil, 2.5; vitamin mix d, 1.5; mineral mix e, 0.5, and carboxymethyl cellulose, 2. c Either Peruvian fish meal, defatted soybean meal, Acetes sp., meat and bone meal, copra meal, wheat flour, rice bran, corn meal or squid meal. d Commercial vitamin mix (mg or MIU/kg dry diet): thiamin, 54; riboflavin, 108; pyridoxine, 84; cyanocobalamine, 0.3; niacin, 216; pantothenic acid, 6; biotin, 0.015; folic acid, 18; inositol, 450; Stable C, 1500; menadione, 36; tocopherol, 247; carotene, 3.0 MIU and calciferol, 0.6 MIU. e Commercial mineral mix (g/kg dry diet): P, 9.6; Ca, 9.6; Mg, 1.2; Fe, 0.12; Zn,.336; Cu, 0.168; K, 6; Co, ; Mn, 0.128; Se, ; Mo, ; Al, 0.002; I, 0.32; B, ; Ni, drying for analysis. Diets and fecal matter samples were analyzed in triplicate for proximate composition (Association of Official Analytical Chemist (AOAC), 1990) and Cr 2 O 3 (Carter et al., 1960). The apparent digestibility coefficients for dry matter (ADMD), crude protein (ACPD), crude fat (ACFD), crude fiber (ACFbD), nitrogen-free extract or NFE (ANFED), and crude ash (AAD) of the RF and test diets were computed using the formula described by Spyridakis et al. (1989) as follows: ADC CP ð%þ ¼100 ð100 %Cr 2 O 3diet =Cr 2 O 3feces %CP feces =%CP diet Þ The ADC for nutrients in feedstuffs were determined by the following formula: ADC CP ð%þ ¼100=30 ½Test fð70=100þrfgš where: Test = ADC of CP in the test diets, RF = ADC of CP in RF. The ACPD values were also recomputed to account for the relative contribution of the nutrient from the RF and the test ingredient according to the equation suggested by Forster (1999).

4 256 M.R. Catacutan et al. / Aquaculture 216 (2003) Statistical analysis Data on digestibility coefficients were analyzed with ANOVA and the Duncan Multiple Range Test using the SAS package for the IBM (SAS Institute, 1988). Differences between means were considered significant at P < Results The proximate nutrient content of test diets showed that crude protein and crude fat levels ranged from 34% to 54.3% and 4.8% to 10.8%, respectively, while that in feedstuffs ranged from 7.8% to 78.5% and 1.3% to 13%, respectively (Table 2). The NFE of diets with feedstuffs from plant sources ( %) were higher than diets with feedstuffs from animal sources ( %). Dietary ash ranged from 12.9% to 22%. Fecal matter egested by crabs throughout the collection period showed an even distribution of the green color from Cr 2 O 3. Fecal collection period was the longest in crabs fed RF and the shortest was in crabs fed copra meal. The ADMD of RF and test diets were significantly higher than that of meat and bone meal with significantly highest values in squid meal and corn meal (Table 3). These two feedstuffs had also significantly high ACPD values (97.6% and 96.4%, respectively) although the mean ACPD value for all feedstuffs was 95.3 F 0.4%. The ACFbD of feedstuffs ranged from 89.4% to 96.6% with significantly high value in squid meal. The ANFED of diet with corn meal was significantly the highest followed by wheat flour and lowest in diets containing meat and bone meal and Acetes sp. The ash component of squid meal was most digestible followed by Peruvian fish meal. Among the plant feedstuffs, AAD of corn meal and defatted soybean meal were similar to Peruvian fish meal while that of copra meal, wheat flour, and rice bran were lowest and similar to meat and bone meal. The crude fat of carbohydrate-rich plant feedstuffs was more digestible than that of protein-rich animal feedstuffs. The ACFD increased as dietary NFE of feedstuffs increased Table 2 Proximate nutrient composition (%) in dry matter of feedstuffs and test diets (in parentheses) Ingredients Crude protein Crude fat Crude fiber NFE a Ash Animal feedstuffs Peruvian fish meal 68.3 (48.9) 5.9 (8.4) 0.8 (2.1) 7.7 (23.6) 17.3 (17.0) Squid meal 78.5 (54.3) 5.5 (7.6) 1.3 (3.6) 6.7 (18.7) 8.0 (15.8) Acetes sp (47.8) 3.9 (7.5) 3.6 (3.5) 7.6 (24.5) 16.3 (16.7) Meat and bone meal 46.8 (42.5) 9.6 (9.4) 2.0 (3.7) 7.5 (22.4) 34.1 (22.0) Plant feedstuffs Copra meal 21.9 (34.0) 6.4 (10.4) 11.0 (4.3) 53.1 (37.5) 7.6 (13.8) Wheat flour 13.9 (36.1) 1.5 (4.8) 0.8 (3.7) 83.2 (42.5) 0.6 (12.9) Rice bran 12.0 (35.1) 13.0 (10.8) 6.2 (4.1) 60.4 (36.2) 8.4 (13.8) Corn meal 7.8 (34.2) 4.7 (8.9) 2.6 (4.0) 83.1 (39.9) 1.8 (13.0) Defatted soybean meal 46.0 (43.8) 1.3 (6.6) 4.2 (4.1) 42.7 (31.3) 5.8 (14.2) a Nitrogen-free extract.

5 M.R. Catacutan et al. / Aquaculture 216 (2003) Table 3 The apparent digestibility coefficients (%) of dry matter (ADMD), crude protein (ACPD), crude fat (ACFD), crude fiber (ACFbD), nitrogen free extract (ANFED), and ash (AAD) of the reference diet and feedstuffs for the mud crab * RF and test ingredients ADMD ACPD ACFD ACFbD ANFED AAD RF Diet 90.0 F F F F F F 1.1 Animal feedstuffs Peruvian fish meal 89.9 F 0.1 bc 94.8 F 0.1 cd 81.0 F 0.9 e 89.4 F 0.3 e 93.2 F 0.1 bc 76.0 F 0.4 b Squid meal 93.6 F 0.3 a 97.6 F 0.2 a 87.8 F 0.8 d 96.6 F 0.2 a 93.1 F 0.4 bc 82.2 F 0.9 a Acetes sp F 0.7 c 94.9 F 0.4 cd 87.2 F 1.4 d 92.9 F 0.5 d 87.6 F 0 d 70.1 F 0.7 cde Meat and bone meal 85.2 F 0.3 d 95.0 F 0.1 cd 87.2 F 0.7 d 90.2 F 0.3 e 85.6 F 0.3 e 64.4 F 1.0 f Plant feedstuffs Copra meal 89.4 F 0.8 bc 94.3 F 0.3 d 95.0 F 0.4 a 94.5 F 0.4 c 91.6 F 1.1 c 64.9 F 3.7 fe Breaf flour 90.6 F 0.3 b 95.2 F 0.1 c 90.6 F 0.4 c 94.6 F c 94.0 F 0.2 b 65.6 F 1.4 fe Rice bran 89.2 F 1.2 bc 94.2 F 0.4 d 93.3 F 0.2 ab 94.4 F 0.6 c 92.4 F 0.7 bc 67.4 F 3.2 def Corn meal 93.2 F 0.3 a 96.4 F 0.1 b 94.5 F 0.3 ab 96.1 F 0.2 ab 95.8 F 0.2 a 74.9 F 1.0 bc Defatted soybean meal 90.9 F 0.5 b 95.5 F 0.3 c 92.1 F 0.6 bc 95.2 F 0.3 bc 92.5 F 0.5 bc 71.6 F 1.5 bcd * Means F S.E.M. with the same superscript within the same column are not different ( P < 0.05). with a correlation coefficient (r 2 ) ranging from 0.74 to The lowest ACFD was in diet with Peruvian fish meal. The ACPD values ranged from 94.2% to 97.6% and there were no differences between plant and animal sources. These were recomputed based on the examples of Forster (1999). Results had differences ranging from 0.17% to 6.13% while for corn meal it was 25%. 4. Discussion The measurement of digestibility coefficients in aquatic animals is quite difficult especially in obtaining reproducible results. There are recommendations made by Lee and Lawrence (1997) to standardize and improve feed digestibility methodologies for crustaceans that include procedural steps for accuracy in using chromic oxide as indicator. Our study has followed these steps (pooling of fecal samples collected over many days from several crabs for each replicate, keeping samples in 80 jc and freeze drying, marker added at 1.0%, fecal collection started after a week of feeding, and all samples were compared on dry weight basis) and the RF, that has been fed for 2 weeks as recommended, has ADMD (>80%) and ACPD (94.4%) values considered best for a reference feed (Lee and Lawrence, 1997). The fecal collection period in the RF fed crabs was longest which could indicate good assimilation. The acceptability of the digestibility results was further enhanced by the observation that crab fecal pellets had an even distribution of the green colored marker. Uneven distribution of the Cr 2 O 3 in the fecal strand in some crustacean species has been reported which could lead to false estimates, but collecting most of the egesta narrows down the calculation errors (Forster and Gabbott, 1971; Bordner et al., 1983; Deering et al., 1996; Jones and de Silva, 1997).

6 258 M.R. Catacutan et al. / Aquaculture 216 (2003) The test diets were efficiently utilized by the mud crab as indicated by the high ADMD values (85.2% to 93.6%). In P. vannamei, purified feedstuffs are efficiently digested compared with practical feedstuffs with ADMD ranging from 21.4% to 91.4% (Akiyama et al., 1989). A tendency of ADMD to decrease as dietary fiber and ash content of the ingredients increased is observed in P. setiferus (22% to 100% while RF ADMD is 57.3%) and the swamp crayfish, Procambarus clarkii (34.7% to >100% while RF ADMD is 76.5%), in diets testing 15 kinds of feedstuffs of plant and animal sources (Reigh et al., 1990; Brunson et al., 1997). This trend is not observed in the Australian freshwater crayfish (Jones and de Silva, 1997) and also in this study possibly because the AAD of test diets and the ADMD of RF were high. The protein in feedstuffs tested were all highly digestible to mud crab. Crustaceans are proficient at digesting proteins as shown by the high protein to energy ratios in these species compared to those in fish (Lee and Lawrence, 1997). The difference in the NFE content of plant and animal feedstuffs, however, had a pronounced effect on the ACFD of feedstuffs of animal sources ( %) compared with feedstuffs of plant origin ( %), but had no effect on the ADMD values (Table 3). Similar results had also been noted in P. vannamei which showed the associative effect of starches of various origin (35% of the diet) affecting more the ACFD (76.6% to 84.8%) than the ACPD (94.1% to 97.8%) (Cousin et al., 1996). In the same species, a difference in the ACPD of the RF and test diets having the same carbohydrate source may indicate associative effects (Davis and Arnold, 1993). Increasing dietary carbohydrate can affect ADMD of formulated diets in P. monodon but had no effect on the digestibility of lipid and protein (Catacutan, 1991). In crayfish, 30% of dextrin in the diet has no effect on the ACPD values (Nose, 1964). The associative effects of nutrients in diets of crustaceans (marine shrimp and crayfish) have been reported to affect feed digestibility especially the interactions of plant meals rich in carbohydrate and animal meals rich in protein (Lee and Lawrence, 1997). It is clear in this study that for mud crabs, the relative amounts of dietary protein and NFE had an effect on the ACFD but not on ADMD. In P monodon, increasing dietary carbohydrate could increase the crude fat in the feces (Catacutan, 1991). However, no data has been available to understand the associative effects among feed ingredients in crustaceans (Lee and Lawrence, 1997). The digestibility of carbohydrates in crustaceans has been reported to vary. It is less assimilated in formulated diets compared with protein and lipids in P. stylirostris (Fenucci et al., 1982) and also in P. setiferus and P. aztecus (Condrey et al., 1972). InP. serratus, diets with 47.5% of different carbohydrate sources were efficiently assimilated compared with P. platycerus (Forster and Gabbott, 1971). In this study, the NFE of feedstuffs (6.7% to 83.2%) were utilized well ( %) but lower values were obtained for Acetes sp. and meat and bone meal ( %). The reason could be the high ash content of these two feedstuffs (16.3% and 34.1%, respectively) compared to the rest ( %), except for fish meal. Forster and Gabbott (1971) reported that ash component of formulated feed is assimilated at 32% by prawns while in crayfish, it is absorbed at 17% to 73% (Jones and de Silva, 1997). The AAD of feedstuffs in this study were high ranging from 64.4% to 82.2%. Based on dry matter, the exoskeleton of S. serrata and P. monodon is 63 65% ash (Sarac et al., 1994; Catacutan, 2002) while the whole body of S. serrata contains 41 48% (Sheen and Wu, 1999; Catacutan, unpublished). The high level of ash in the mud crab exoskeleton and the observation that crustaceans consume their exuvia after ecdysis could

7 M.R. Catacutan et al. / Aquaculture 216 (2003) probably explain the high AAD values of feedstuffs in this study. Calcium salts is present in high quantity in cuticles of many crustacean species (Welinder, 1974, 1975). The loss of minerals during molting could further explain the high AAD in this study. The difference in AAD values could be due to different minerals at varying levels in these feedstuffs that are important to mud crab. An important component of crustacean exoskeleton is chitin and when added in formulated diet at 1 4%, it is digested from 33% to 52% by three penaeid shrimps (Clark et al., 1993). In our study, the AAD of Acetes sp., also a crustacean, was 70% but significantly lower than that of Peruvian fish meal or squid meal. In P. stylirostris, the protein in test diets with the crustacean feedstuffs, such as shrimp and crab meals, had low digestibility compared to rice bran and soybean meal (Brunson et al., 1997). In the swamp crayfish, P. clarkii, the ACPD of rice bran (94%), solvent extracted soybean meal (95%), wheat flour (96%), and corn grain (97%) obtained using RF and test diets in a 70:30 ratio were similar to the results obtained in this study (Reigh et al., 1990). Soybean meal protein is considered to be highly digestible to many crustacean species (Forster and Gabbott, 1971; Catacutan, 1997; Mu et al., 2000). In P. setiferus (Brunson et al., 1997), the ADMD and ACPD of corn grain were lower than soybean meal but the opposite was observed in crayfish (Reigh et al., 1990) and also in this study. The similarity of digestibility coefficients of feedstuffs in crayfish and mud crab could be due to natural feeding habit. The swamp crayfish is an omnivore (Wienicki, 1984) while the young mud crab showed a preference for detritus and the adult for crustaceans and fish (Prasad and Neelakantan, 1998). Forster (1999) suggested a modification on the method of calculating ADC that would account for the relative contribution of the nutrient from the RF and test feedstuff to the combined test diet. In the examples of Forster (1999) using published data, the recalculated ACPD values had the biggest difference of 8.1%, while in this study (except for corn meal), it ranged only from 0.17% to 6.13%. Big differences in values are obtained when there is a large difference in the level and digestibility of nutrient in test feedstuffs from those in the RF. This is the case of corn meal (7.8% crude protein) and the difference in Forster s (1999) formula was 25% from the original value. Crabs have been reported to cease feeding during molting (Zhou et al., 1998). In this study, we adjusted feeding rate right after molting. Feeding rate and feeding frequency had been found to have no effect on the protein digestibility in the freshwater prawn in experiment using Cr 2 O 3 as indicator (Taechanuruk and Stickney, 1982). There are many factors that can affect digestibility work in aquaculure species, but the acceptability of results in this study rested on the recommended procedures that were followed. Nutrients in feedstuffs of animal and plant origin were digested well by the mud crab, S. serrata. The digestibility of lipid in protein-rich animal feedstuffs was low compared to carbohydrate-rich plant feedstuffs. For this species, plant feedstuffs can be utilized as a major source of nutrients for effective and cheaper diet cost. Acknowledgements The authors would like to acknowledge the commendable technical assistance of Ms. Ellen Flor Doyola and Mr. Hernando Alcalde.

8 260 M.R. Catacutan et al. / Aquaculture 216 (2003) References Akiyama, D.M., Coelho, S.R., Lawrence, A., Robinson, E.H., Apparent digestibility of feedstuffs by the marine shrimp Penaeus vannamei Boone. Nippon Suisan Gakkaishi 55, Association of Official Analytical Chemist (AOAC), In: Herlich, K. Official Methods of Analysis, 15th ed. AOAC, Arlington, VA. Bordner, C.E., D Abramo, L., Conklin, D.E., Assimilation of nutrients by cultured hybrid lobsters (Hoomarus sp.) fed experimental diets. J. World Aquac. Soc. 14, Brunson, J.F., Romaire, R., Reigh, R.C., Apparent digestibility of selected ingredients in diets for white shrimp Penaeus setiferus L. Aquac. Nutr. 3, Carter, J.F., Bolin, D.W., Erickson, D., Evaluation of forages by the agronomic difference method and the chromogen oxide indication techniques. North Dakota Agric. Extn. Bull., vol Fargo, North Dakota, 55 pp. Catacutan, M., Apparent digestibility of diets with various carbohydarte levels and the growth response of Penaeus monodon. Aquaculture 95, Catacutan, M., Protein and dry matter digestibility of feedstuffs in complete diets for Penaeus monodon. In: Zhou, Y., Zhou, H., Yao, C., Lu, Y., Hu, F., Cui, H., Din, F. (Eds.), Proceedings of the Fourth Asian Fisheries Forum, Beijing, October Asian Fisheries Society, China Ocean Press, pp Catacutan, M., Growth and body composition of juvenile mud crab, Scylla serrata, fed different dietary protein and lipid levels and protein to energy ratios. Aquaculture 208, Clark, D.J., Lawrence, A.L., Swakon, D.H., Apparent chitin digestibility in penaeid shrimp. Aquaculture 109, Condrey, R., Gosselink, J., Bennett, H., Comparison of the assimilation of different diets by Penaeus setiferus and P Aztecus. Fish. Bull. 70, Cousin, M., Cuzon, G., Guillaume, J., AQUACOP Digestibility of starch in Penaeus vannamei: in vivo and in vitro on eight samples of various origin. Aquaculture 140, Davis, D.A., Arnold, C., Evaluation of five carbohydrate sources for Penaeus vannamei. Aquaculture 114, Deering, M.J., Hewitt, D.R., Sarac, H.Z., A comparison of inert markers used to estimate protein digestibility in the leader prawn Penaues monodon. J. World Aquac. Soc. 27, Fenucci, J., Fenucci, A.C., Lawrence, A., Zein-Eldin, Z., The assimilation of protein and carbohydrate from prepared diets by the shrimp Penaeus stylirostris. J. World Maric. Soc. 13, Forster, I., A note on the method of calculatin digestibility coefficients on nutrients provided by single ingredients to feeds of aquatic animal. Aquac. Nutr. 5, Forster, J.R.M., Gabbott, P.A., The assimilation of nutrients from compounded diets by the prawns Palaemon serratus and Pandalus platyceros. J. Mar. Biol. Assoc. UK 51, Jones, P.L., de Silva, S., Apparent nutrient digestibility of formulated diets by the Australian freshwater crayfish Cherax destructor Clark (Decapoda, Parastacidae). Aquac. Res. 28, Keenan, C., Davie, P., Mann, D., A revision of the genus Scylla De Haan, 1833 (Crustacean:Decapoda:Brachyura:Portunidae). Raffles Bull. Zool. 46, Koshio, S., Castell, J.D., O Dor, R.K., The effect of different dietary energy levels in crab-protein-based diets on digestibility, oxygen consumption, and ammonia excretion of bilaterally eyestalk-ablated and intact juvenile lobsters Homarus americanus. Aquaculture 108, Lee, D., Study on digestion and absorption of protein in artificial feeds by four species of shrimps. China Fish. Mon. 208, 2 4. Lee, G.P., Lawrence, A., Digestibility. In: D Abramo, L., Conklin, D., Akiyama, D.Crustacean Nutrition Advances in World Aquaculture, vol. VI. World Aquaculture Society, Baton Rouge, LA, USA, pp Mu, Y., Lam, T., Guo, J., Shim, K., Protein digestibility and amino acid availability of several protein sources for juvenile Chinese hairy crab Eriocheir sinensis H Milne-Edwards (Decapoda, Grapsidae). Aquac. Res. 31, Nose, T., Protein digestibility of several test diets in cray and prawn fish. Bull. Freshw. Fish Res. Lab. (Tokyo) 14,

9 M.R. Catacutan et al. / Aquaculture 216 (2003) Prasad, P.N., Neelakantan, B., Food and feeding of the mud crab, Scylla serrata, Forsskal (Decapoda:Portunidae) from Karwar waters. Indian J. Fish. 35, Reigh, R.C., Braden, S., Craig, R.J., Apparent digestibility coefficients for common feedstuffs in formulated diets for red swamp crayfish Procambarus clarkii. Aquaculture 84, Sarac, H.Z., McMeniman, N.P., Thaggard, H., Gravel, M., Tabrett, S., Saunders, J., Relationships between the weight and chemical composition of exuvia and whole body of the black tiger prawn Penaeus monodon. Aquaculture 119, SAS Institute Inc., SAS/STAT User s Guide, Release 6.03 Edition. SAS Institute, Cary, NC, 1028 pp. Sheen, S., Wu, S., The effects of dietary lipid levels on the growth response of juvenile mud crab Scylla serrata. Aquaculture 175, Smith, L., Lee, P., Lawrence, A., Strawn, K., Growth and digestibility by three sizes of Penaeus vannamei Boone: effects of dietary protein level and protein source. Aquaculture 46, Spyridakis, P., Metailler, R., Gabaudan, J., Studies on nutrient digestibility in European sea bass (Dicenntrarchus labrax): 1. Methodological aspects concerning faeces collection. Aquaculture 77, Taechanuruk, S., Stickney, R., Effects of feeding rate and feeding frequency on protein digestibility in the freshwater shrimp (Macrobrachium rosenbergii). J. World Maric. Soc. 13, Teshima, S., Kanazawa, A., Digestibility of dietary lipids in the prawn. Bull. Jpn. Soc. Sci. Fish. 49, Welinder, B.S., The crustacean cuticle: I. Studies on the composition of the cuticle. Comp. Biochem. Physiol. 47A, Welinder, B.S., The crustacean cuticle: II. Deposition of organic and inorganic material in the cuticle of Astacus fluviatilis in the period after molting. Comp. Biochem. Physiol. 51B, Wienicki, C., Assimilation efficiency by Procambarus clarkii fed elodea (Egera densa) and its products of decompositon. Aquaculture 36, Williams, G., Field, D., Development of hatchery practices for the culture of mud crabs in Northern Australia. World Aquac. 30, Zhou, S., Shirley, T.C., Kruse, G.H., Feeding and growth of the red king crab Paralithodes camtschaticus under laboratory condition. J. Crustac. Biol. 18,