Abstract
The effects of arginine levels in diets on growth performance, survival, and haemato-biochemical responses and gene expression of genetically improved farmed tilapia (GIFT) juveniles raised in inland saline water (ISW) of 10 ppt were evaluated through a 60-day growth trial. Seven isoproteinaceous (⁓320 g protein/kg), isolipidic (80 g/kg) and isoenergetic (16.8 MJ DE/kg) diets with graded levels of arginine viz. A10 (10 g/kg), A12.5 (12.5 g/kg), A15 (15.0 g/kg), A17.5 (17.5 g/kg), A20 (20.0 g/kg), A22.5 (22.5 g/kg) and A25 (25.0 g/kg) were prepared. Acclimated GIFT juveniles (3.75 ± 0.017 g) were randomly assigned into seven treatments in triplicate with 15 fish/replicate and fed with respective diets thrice a day on a satiation basis. The percent weight gain, specific growth rate, protein efficiency ratio, whole carcass protein, tissue alanine and aspartic acid aminotransferase activities, serum total protein, albumin and globulin concentration and expression of IGF-1 & IGF-1R genes of fish significantly increased, while feed conversion ratio significantly decreased with increasing arginine in the diet up to 17.5 g/kg and decreased thereafter. Additionally, white blood cell count increased with rising arginine levels in the diet. However, body indices, survival, whole carcass lipid, total ash and essential amino acids contents, activities of digestive and antioxidant enzymes, serum glucose level and blood haemoglobin level and red blood cell count of fish remained unchanged for different treatments. Based on broken-line regression and second order polynomial regression models in relation to hepatic IGF-1 gene expression and percent weight gain, the dietary optimal arginine level was found to be 15.97 and 16.76 g/kg and 17.06 and 17.41 g/kg, respectively with the optimum range of 15.97 to 17.41 g/kg for successful culture of GIFT in ISW of 10 ppt salinity.
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