ALLMAN, Andrea/L*; PLACE, Allen/R; Center of Marine Biotechnology, Baltimore MD: The effect of dietary chitin and cellulose on growth and digestive enzyme production in the juvenile blue crab, Callinectes sapidus.

Blue crab (Callinectes sapidus (Rathbun)) hatchery technology is being developed at the Center of Marine Biotechnology (Baltimore, MD). To more efficiently produce juveniles and adults for research purposes, the appropriate diet needs to be formulated. Recent findings indicate that many species of crustaceans have the capabilities to digest various forms of fiber. Cellulose, followed by chitin, composes the largest biomass worldwide, providing an energetic advantage for animals that can digest them. We performed a 12-week experiment, using a commercial pelleted shrimp diet for which we replaced 20% of the wet weight (comprised of ground wheat derivatives) with either chitin or cellulose. We used a recirculating, compartmentalized system that we developed to maintain near optimal water quality values while preventing cannibalism. Relative growth ((log(final weight) � log(initial weight)) / time) was significantly lower in the chitin-fed crabs (0.0038) than in either the cellulose-fed crabs (0.0058) or the control group (0.0062) (p < 0.0001). There was a substantial difference in food conversion efficiency (wet weight gained / wet weight fed) between crabs fed chitin (0.23) and cellulose (0.40) or the control diet (0.45) (p < 0.0001). All of the growth parameters investigated (molt increment, molt frequency, and total number of molts per crab) were significantly lower in the chitin-fed treatment than the other two treatments (p < 0.05). To determine whether diet affected the presence and quantity of cellulase and chitinase, enzyme assays are being performed on the gut and hepatopancreas. Cellulase was detected in the foregut and hepatopancreas using a dye-linked substrate method, and the results for chitinase are pending.