Effect of dietary protein level on growth and metabolism of GIFT juveniles reared in inland ground saline water of medium salinity

ABSTRACT A 60-day feeding trial was conducted to study the effect of varying levels of dietary protein on growth metrics, hemato-biochemical status, and metabolic responses of GIFT tilapia juveniles reared in inland ground saline water (IGSW) of 15 g/l. A random distribution of 315 acclimated fish (avg. wt. 4.01 ± 0.01 g, stocking density 15 fish/tank) was done in seven experimental groups—20% (CP20), 25% (CP25), 30% (CP30), 35% (CP35), 40% (CP40), 45% (CP45), and 50% (CP50)—in triplicates following a completely randomized design (CRD). Weight gain (WG), metabolic growth rate (MGR), feed efficiency ratio (FER), and protein growth rate (PGR) showed higher quadratic relations (R2 = 0.93, 0.96, 0.92, 0.90 respectively) with highest (P < 0.05) values in the CP40 group. Protein efficiency ratio (PER) significantly (P < 0.05) decreased with increase in dietary protein levels. Higher (P < 0.05) quadratic relations of muscle and hepatic AST (R2 = 0.71, 0.75) and ALT (R2 = 0.77, 0.69) activities, hemoglobin (Hb) content (R2 = 0.87), hematocrit (Hct), value (R2 = 0.93), and red blood cell (RBC) count (R2 = 0.88) were found in groups fed higher levels of dietary protein than their lower protein-fed counterparts. Muscle LDH and MDH activities were the highest (P < 0.05) in CP20 and CP50 group respectively with strong linear and quadratic relationships. The lowest (P < 0.05) serum glucose level was found in the CP40 group. Second-order polynomial regression analysis indicated that 41.85% dietary protein is optimum with respect to growth metrics, nutrient utilization, and metabolic status of GIFT tilapia juveniles in IGSW of 15 g/l.