Dietary lysine requirement of genetically improved farmed tilapia (GIFT) juvenile reared in inland saline water of 10 ppt salinity

Abstract

A 60-day feeding trial was conducted to optimize the dietary lysine (LYS) requirement of juvenile genetically improved farmed tilapia (GIFT) reared in inland saline water (ISW) of 10 ppt salinity. Seven isonitrogenous (370 g crude protein/kg), isolipidic (80 g crude lipid/kg) and isocaloric (16.66 MJ digestible energy/kg) purified diets were formulated and prepared with graded LYS levels viz., 12.3 (L12.3), 14.7 (L14.7), 17.2 (L17.2), 19.6 (L19.6), 22.3 (L22.3), 24.8 (L24.8) and 27.2 g/kg (L27.2). GIFT juveniles (mean weight 3.16 ± 0.01 g, 315 numbers) were randomly allocated in triplicate into seven distinct groups following a completely randomized design. The juveniles were fed three times daily to apparent satiation level with the respective experimental diet. The results indicated that growth and nutrient utilization parameters were significantly (p < 0.05) altered by the various dietary LYS levels. These parameters exhibited an increasing trend from lowest dietary LYS level (12.3 g/kg) to 19.6 g/kg dietary LYS, and subsequent additional dietary LYS supplementation showed a declining trend. Significantly greater final weight, weight gain percentage, specific growth rate, protein efficiency ratio, apparent net protein retention and lower feed conversion ratio were found in the 19.6 g/kg LYS fed group than other groups. Different levels of LYS inclusion did not affect (p > 0.05) the body indices, survival and whole-body moisture and ash content of fish. An increment in dietary LYS up to 19.6 g/kg resulted in an increase in whole-body protein level and a decline in lipid level. The whole-body essential amino acid compositions of juveniles were not changed with various dietary LYS levels, whereas the non-essential amino acids increased with increasing dietary LYS levels up to 19.6 g/kg and decreased thereafter. Juveniles fed with high LYS containing diets exhibited higher aspartate aminotransferase and alanine aminotransferase activities, while digestive enzyme activities were unaffected. Serum protein, albumin, globulin, hemoglobin and white blood cell count changed with various dietary LYS levels. Based on broken-line linear and second-order polynomial regression analysis, the optimal dietary LYS requirements range was found to be 19.3–20.7 g/kg of the diet for GIFT juvenile reared in ISW of 10 ppt salinity.