Early Weaning of Sea Bass (D. labrax) Larvae: Effects on Growth Performance and Digestive Enzyme Activities

In this study, effects of early weaning of sea bass (D. labrax) by microparticulate food on larval development and digestive enzyme activities, acid protease and alkaline protease were investigated until day 40. Larval rearing was conducted in closed sea water systems. Experiments were triplicated on 3 different weaning protocol that introduced on day 15 (MD 15), day 20 (MD20) and day 25 (MD25) and also no microparticulate diet (MD) distributed in the control group. At the end of the experiment at 40-day, larval growth was calculated and the best values were obtained from MD25. Statistical differences among groups were not important (P>0.05) whereas MD15 was found different than the other groups (P<0.05). Also, survival rates were calculated as 3.6%, 14.7%, 43.6%, and 34.1% for the experimental groups, respectively. MD15 and MD20 groups were found different than the other groups (P<0.05). Nevertheless, activity of alkaline protease was detected synchronously by mouth opening and exogenous feeding and also increased by larval development. According to histological analysis, pancreas was observed by mouth opening and similarly developed with increasing of larval age. Alkaline protease activity changed by nutritional composition of feed and especially shifting of feed affected the enzymatic activity. There was no differences among the experimental groups (P>0.05) while control group was found statistically different (P<0.05). According to histological analysis, gastric glands and formation of functional stomach were observed on day 24-25 in all experimental groups. Acid protease activity firstly detected at 25 DAH. Control group was found different than the other groups (P<0.05). Finally, in terms of both growth parameters and survival rate and digestive enzyme activities it is clearly concluded that MD supplementation could be started after 25 DAH in D. lahrax larviculture.