Feeding graded levels of protein to genetically improved farmed Tilapia (GIFT) juveniles reared in inland saline water: Effects on growth and gene expression of IGF I, IGF-IR and IGF-BPI

Abstract A 60-day feeding trial was conducted on Genetically Improved Farmed Tilapia (GIFT) juveniles in inland saline water (ISW) of 10 ppt salinity. Seven isoenergetic (400 kcal DE/100 g), isolipidic (6%) and hetero‑nitrogenous (20, 25, 30, 35, 40, 45 and 50% CP) experimental diets were formulated and prepared using purified ingredients. Three hundred and fifteen GIFT juveniles (average body weight 2.68 ± 0.01 g) were distributed in seven experimental groups viz., T20 (20% CP), T25 (25% CP), T30 (30% CP), T35 (35% CP), T40 (40% CP), T45 (45% CP) and T50 (50% CP) in triplicates following a completely randomized design (CRD) with the stocking density of 15 fish/tank (92 cm diameter X 45 cm height) with 200 L water volume. Fishes of different experimental groups were fed with respective experimental diets thrice daily at satiation level. Results indicated that dietary crude protein has significant (p  I) and Insulin like growth factor I receptor (IGF IR) were highly correlated with WG% (r = 0.92 and r = 0.97, respectively). The expression of IGF IR was also correlated with IGF-I expression (r = 0.93). According to broken-line and second-order polynomial regression analysis in relation to WG% and expression of hepatic IGF-I gene, the optimum dietary crude protein levels of GIFT juveniles reared in inland saline water of 10 ppt salinity were found to be 37.37, 37.72, 40.92 and 38% crude protein with isoenergetic of 400 kcal DE/100 g diet, respectively.