Effect of dietary methionine and energy on growth performance and feed utilization of juvenile Penaeus vannamei reared under hyperosmotic salinity

This study assessed the impact of varying dietary methionine (Met) and digestible energy (DE) levels on the growth performance, feed utilization, and glycemia in hemolymph of juvenile Penaeus vannamei reared under hyperosmotic salinity (43-48 g L-1). A 2 x 3 factorial design was used to evaluate six diets, varying in two DE levels (15.7 and 16.6 MJ kg(-1), DM basis), achieved through soybean oil addition, and three Met levels (7.6, 8.5, and 9.9 g kg(-1), DM basis), adjusted with crystalline DL-Met-Met supplementation. Dietary crude protein was maintained at 371 +/- 3.0 g kg(-1) (DM basis). Shrimp of 2.9 +/- 0.04 g were reared at 100 animals m(-2) in forty 0.5-m(3) tanks for 60 days. No differences were found in shrimp survival, specific growth rate, weight gain, and feed conversion ratio (FCR) across the different DE and Met levels (P>0.05). However, dietary DE levels significantly influenced daily gross energy intake (P<0.01) and daily DE intake (P<0.01). Dietary Met levels significantly affected daily Met intake (P<0.01) and total sulfur amino acid intake (P<0.01). Glucose concentration in shrimp hemolymph was significantly influenced by dietary Met levels (P = 0.02), with higher levels leading to increased glucose concentrations. Results suggested that while Met levels affect certain metabolic responses, they did not translate into enhanced growth performance under hyperosmotic conditions. Experimental diets met the shrimp's dietary requirements for energy and Met, with no additional benefits observed from increased levels.