STUDIES ON THE ROLE OF PEPTIDASE AND POWDER SOYBEAN LECITHIN IN MICROPARTICLE DIETS FOR RED SEA BREAM PAGRUS MAJOR LARVAE

This study investigates the effects of exogenous enzyme supplementation on the digestibility of microparticle diets (MD). Powder soybean lecithin and gluten were used instead of paste soybean lecithin for evaluating its effect on the leaching rate inMD. Three kinds of MD (MD-T;MD-S;MD-U)were prepared.Based on formulation of MD-S, MD-T included powder soybean lecithin instead of paste soybean lecithin and gluten as a binder.MD-U was supplied with 0.1 % of peptidase.The other ingredients were the same in the three diets.Within the first 15 minutes of submersion in water, the leaching rate for MD-T (35.5%) was lower than for MD-S (46.8 %)and MD-U (45.8%).The first feeding red sea bream larvae were fed the three above mentioned MD and live food (LF)as a control.The trial lasted until 20 days after hatching.Final survival rate was highest in LF treatment (86.3%), followed by MD-T(20.7 %)treatment, which was significantly higher (P <0.05)than the results for MDS (13.3%)andMD-U(13.6 %)treatments.Final total length (TL)of larvae fed LF was with 6.14 ±0.49mm significantly larger (P <0.05)than for those fed withMD, which reached at sizes ranged from 4.23 ±0.30mm (MD-S)to 4.46 ±0.30mm (MD-T).There were no significant differences in growth among MD treatments.Histological analysis of digestive epithelium of larvae showed thick and well-developed intestine folds at 12 days after hatching in both of LF andMD treatments.However, the intestine epithelium of larvae fed onMD appeared thin and most cell desquamation were observed at 18 days after hatching, indicating limited digestive capacity after 12 days after hatching and led to sharp decline of survival rate inMD treatments thereafter.Daily increments for protein, DNA and RNA as well as the ratio of RNA/DNA were higher in larvae fed LF compared to the respective values obtained for those fedMD.Larvae fedMD-T showed higher value of the above parameters than those fedMD-S andMD-U, suggesting larvae had a better nutritional condition in MD-T treatment than those inMD-S andMD-U treatments.The results indicated that supplementation of peptidase could not facilitate the digestion of MD for red sea bream larvae.However, using powder soybean lecithin and gluten could reduce the leaching rate from MD and consequently improved larval survival and growth.