Dietary lysine requirement of juvenile Pacific white shrimp, Litopenaeus vannamei (Boone, 1931) reared in inland saline water of 10 ppt salinity

A feeding trial of 60 days was conducted to assess the dietary lysine requirement of juvenile Litopenaeus vannamei reared in inland saline water. Seven isonitrogenous (~ 360 g crude protein/kg feed), isolipidic (~ 60 g crude lipid/kg feed) and isocaloric (~ 18 MJ gross energy/kg feed) semi-purified test diets with graded lysine levels viz., 13.7 (L1), 16.3 (L2), 18.7 (L3), 21.4 (L4), 23.8 (L5), 26.3 (L6) and 28.9 g/kg (L7) were formulated and prepared. Three hundred and seventy-eight L. vannamei juveniles (2.75 ± 0.01 g) were randomly distributed (60 no/m³ or 33 no/m²) into seven test groups in triplicates following a completely randomized design. L. vannamei juveniles were fed to the apparent satiation level four times daily. At the end of the feeding trial, the results indicated that dietary lysine levels have significantly (P < 0.05) affected the growth and nutrient utilization parameters in juvenile L. vannamei. An increase (P < 0.05) in final body weight, weight gain percentage (WG%), thermal growth coefficient (TGC), protein efficiency ratio and protein productive value were observed with the increasing dietary lysine levels from 13.7 to 23.8 g/kg after which a decreasing trend was observed. The relative feed intake and feed conversion ratio showed a decreasing trend from lower dietary lysine levels to higher levels. Survival rates of experimented shrimp were not significantly different (P > 0.05) among the treatment groups. The whole body crude protein and crude lipid content of L. vannamei showed significantly (P < 0.05) increasing and decreasing trends, respectively towards the increasing dietary lysine levels. The hepatopancreatic and muscle protein metabolic enzyme activities, haemocyanin and serum total protein content of L. vannamei varied significantly among the treatment groups. The broken-line linear and second-order polynomial regression analysis of WG% and TGC against the dietary lysine levels indicated that the optimal dietary lysine level with confidence interval (CI) for juvenile L. vannamei reared in inland saline water of 10 ppt salinity is 23.46 (22.59–24.88 g/kg, 95% CI) to 25.24 g/kg (24.27–26.53 g/kg, 95% CI) and 23.26 (22.70–24.15 g/kg, 95% CI) to 25.25 g/kg (24.27–26.53 g/kg, 95% CI) of the diet, respectively.