Effect of a Serine-protease on Performance Parameters and Protein Digestibility of Cultured Oreochromis niloticus Fed Diets with Different Protein Levels

Objective: This study was conducted to investigate the effect of a serine-protease supplementation on growth performance and protein digestibility of cultured Oreochromis niloticus fed diets with different crude protein (CP) levels.Materials and Methods: The diets T1and T2 were formulated to supply 28 and 26% crude protein, respectively.A serine-protease enzyme (Ronozyme ProAct) product with an activity of 75000 Protease (PROT)/g was added to the diets at the level of 0, 200 and 400 mg kgG 1 diet.In this study 384 fish with an initial body weight of average 36.34±3.68g were divided into 6 groups with 4 replicates of 16 fish/replicate.The experimental period extended for 56 days.Results: The weight gain (WG), specific growth ratio (SGR) and protein efficiency ratio (PER), apparent protein digestibility (APD) were significantly increased when T1 and T2 diets were supplemented with protease enzyme while feed conversion ratio (FCR) was significantly decreased.Fish fed T2 diet supplemented with 400 mg kgG 1 protease showed a non-significant difference in final weight, SGR, PER and APD comparing with fish fed T1 diet only.Conclusion: The results indicated that the protease enzyme supplementation can significantly improve growth performance and protein digestibility in O. niloticus.Protease enzyme could be used to reduce the protein content of the diet with maintaining the fish performance.