Effect of dietary methionine levels on growth, carcass composition, physio-metabolic responses and haemato-biochemical parameters of juvenile Pacific white shrimp (Litopenaeus vannamei) reared in inland saline groundwater

Abstract

The salt affected lands and underlying saline groundwater can be useful for viable aquaculture practices for euryhaline species like Pacific white shrimp (Litopenaeus vannamei). At the same time optimization of nutritional requirement is necessary to cultivate the species under captivity in this new environment. The current study was conducted to evaluate the effect of dietary methionine on growth, carcass composition, physio-metabolic responses and haemato-biochemical parameters of juvenile Pacific white shrimp grown in inland saline groundwater of 10 ppt salinity. Seven test diets were prepared for feeding trial with different methionine levels viz., 6.2 (M0), 7.6 (M1.5), 9.3 (M3), 10.7 (M4.5), 12.4 (M6), 14 (M7.5) and 15.3 g/kg (M9). The diets were isocaloric (∼17.5 MJ gross energy/kg), isonitrogenous (∼360 g crude protein/kg) and isolipidic (∼60 g crude lipid/kg) in profile. The acclimated Pacific white shrimp juveniles (2.75 ± 0.01 g) were randomly distributed to seven test groups in triplicates with a stocking density of 18 shrimp per experimental tank (300 L water volume; 366 L capacity). The Pacific white shrimp juveniles were fed four times daily (07:30, 12:00, 18:00 and 22:30 h) using respective test diets on an apparent satiation basis. The study results showed that dietary methionine levels have significant (P<0.05) effect on the growth and nutrient utilization parameters. An increasing trend was observed in weight gain percentage, thermal growth coefficient, protein productive value and protein efficiency ratio with the increasing dietary methionine levels from 6.2 (M0) to 12.4 (M6) g/kg, and followed by a decreasing trend was observed. The values of feed conversion ratio were decreased from lower dietary methionine levels to the optimum methionine level and increased thereafter. The serum haemocyanin, glucose, total protein, cholesterol and triglyceride contents varied significantly (P<0.05) among the treatment groups. Based on the linear and polynomial regression plot of weight gain percentage against the methionine levels in the test diets, it is concluded that the optimal dietary methionine requirement for inland saline groundwater reared Pacific white shrimp juveniles is 10.89–12.02 g/kg of the diet containing 360 g crude protein/kg with 3.5 g cystine/kg.