BIOCHEMICAL-COMPOSITION AND DIGESTIVE ENZYME-ACTIVITY IN LARVAE AND POSTLARVAE OF PENAEUS-JAPONICUS DURING HERBIVOROUS AND CARNIVOROUS FEEDING

The growth, survival, digestive enzyme activity and biochemical composition of Penaeus japonicus (Bate) larvae and postlarvae were measured under three feeding regimes. Larvae were reared through the protozoeal stages using Chaetoceros gracilis. From the first mysis stage, three feeding regimes were used; (A) C. gracilis plus Artemia sp. nauplii, (B) Artemia sp. nauplii alone or (C) C. gracilis alone. No significant difference was found in growth, survival, protein content or lipid content of postlarvae from the treatments receiving the single-feed type, despite the low protein (7%) and highly unsaturated fatty acid content of the alga. Growth of larvae receiving the mixed diet was significantly higher than in the other treatments. Trypsin activity was more strongly influenced than amylase activity by dietary treatment, and differences in the ratio of these enzymes between treatments suggest independent control of their secretion. Trypsin activity recorded in larvae feeding on C. gracilis was up to six time higher than in larvae feeding on Artemia sp. nauplii, apparently in response to the low protein content of the alga. Larvae receiving the mixed diet exhibited an intermediate level of trypsin activity; it is suggested that the ingestion of algae is necessary for optima assimilation of the zooplankton component of the diet.