STUDY ON SUITABLE PROPORTION OF YEAST HYDROLYZATE REPLACEMENT OF FISHMEAL IN FEED OF LITOPENAEUS VANNAMEI

A series of 8 weeks feeding experiment was conducted to estimate the suitable proportion of yeast hydrolyzate (YH) suitable for fishmeal in feed of Litopenaeus vannamei. Supplementation of YH were 0, 2.5%, 5.0%, 7.5%, 10% and 12.5%, respectively. The substitution proportions for fishmeal were 0, 8%, 16%, 24%, 32% and 40%, respectively. The effects of yeast hydrolyzate instead of part fishmeal on the healthy growth of juvenile shrimp were evaluated by assessing the growth performance, digestive enzymes and immune enzymes activities. Each diet was fed to triplicate groups with shrimp initial body weight of (0.630.01) g in a fresh water rearing system. The weight gain rate and specific growth rate of shrimps of Y2.5 and Y5.0 treatments showed no significant differences with the shrimp of Y0 treatment (P0.05), which were significantly higher than that of the other treatments (P0.05). No differences were found between the Y2.5 treatment and Y0 treatment in feed coefficient (P0.05). Feed coefficient of Y2.5 treatment was lower than that of the other substitution treatments (P0.05). Chymotrypsin activities of hepatopancreas in treatments Y5.0 and Y0 were not significant (P0.05), but significantly higher than that of the rest treatments (P0.05). Trypsin activities of hepatopancreas in treatments Y2.5, Y7.5 and Y0 were not significant (P0.05), but significantly higher than that of the rest treatments (P0.05). Polyphenol oxidase activities of shrimp of Y2.5 and Y5.0 were higher than the others (P0.05). Total nitric oxide synthase activities of shrimp of Y0, Y2.5 and Y7.5 were higher than that of the others (P0.05). Serum lysozyme activities of shrimp of Y5.0 and Y7.5 treatment were higher than that of the other treatments (P0.05). Quadratic regression analysis of weight gain against YH replacement ratio of fishmeal indicated that the optimum additive amount was 1.62% and replacement ratio was 5.19% for the maximum weight gain of juvenile shrimp. There was no difference on weight gain of shrimp while the replacement ratio of hydrolyzed yeast to fishmeal to 24%.