Optimal dietary protein requirement of juvenile GIFT Tilapia (Oreochromis niloticus) reared in inland ground saline water

Abstract

Aim: The present study was conducted to optimize the dietary protein level in the diet of Genetically Improved Farmed Tilapia reared in inland ground saline water (IGSW) of 15 ppt ambient salinity. Methodology: Seven iso-caloric (400 kcal digestible energy, DE/100g), iso-lipidic (6%) and hetero-nitrogenous (20-50% crude protein, CP) purified diets were prepared for conducting the feeding trial. Following completely randomized design, the random distribution of 315 acclimatized fish (average body weight 4.01±0.01g) was made in seven groups namely, CP20, CP25, CP30, CP35, CP40, CP45 and CP50 in triplicate with the stocking density of 15 fish per replicate tank. Results: Weight gain percentage, specific growth rate, and expression of insulin like growth factor-I and insulin like growth factor-I receptor with higher quadratic relation (R2=0.94, 0.96, 0.90 and 0.93, respectively) to the dietary crude protein (CP) level significantly increased (p<0.05) up to 40% crude protein and beyond that the values significantly decreased. With higher quadratic (R2=0.83) relation, muscle RNA/DNA ratio was significantly highest in 40% crude protein fed group. With higher quadratic (R2=0.81 and 0.98, respectively) relations, significantly higher protease and lower amylase activities were found in 40, 45 and 50% crude protein fed groups. Interpretation: Second order polynomial regression analysis based on WG%, SGR and IGF-I gene expression revealed that the optimum dietary protein for GIFT juveniles could be 41.84, 40.66 and 42.22%, respectively. This data will be helpful for development of economic and environment-friendly feed for GIFT tilapia culture in inland ground saline water of medium salinity.