Salinity levels affect the lysine nutrient requirements and nutrient metabolism of juvenile genetically improved farmed tilapia (Oreochromis niloticus)

This 62-d research aimed to evaluate the effects of dietary lysine levels (DLL) and salinity on growth performance and nutrition metabolism of genetically improved farmed tilapia (GIFT) juveniles (Oreochromis niloticus). Six diets with lysine supplementation (1 center dot 34, 1 center dot 70, 2 center dot 03, 2 center dot 41, 2 center dot 72 and 3 center dot 04 % of DM) were formulated under different cultured salinities in a two-factorial design. The results indicated that supplemental lysine improved the specific growth rate (SGR) and weight gain (WG) and decreased the feed conversion ratio (FCR). Meanwhile, the fish had higher SGR and WG and lower FCR at 8 parts per thousand salinity. Except for moisture, the whole-body protein, lipid and ash content of GIFT were increased by 8 parts per thousand salinity, which showed that DLL (1 center dot 34 %) increased the whole-body fat content and DLL (2 center dot 41 %) increased whole-body protein content. Appropriate DLL up-regulated mRNA levels of protein metabolism-related genes such as target of rapamycin, 4EBP-1 and S6 kinase 1. However, 0 parts per thousand salinity reduced these protein metabolism-related genes mRNA levels, while proper DLL could improve glycolysis and gluconeogenesis mRNA levels but decrease lipogenesis-related genes mRNA levels in liver. 0 parts per thousand salinity improved GLUT2, glucokinase and G6 Pase mRNA levels; however, sterol regulatory element-binding protein 1 and fatty acid synthase mRNA levels were higher at 8 parts per thousand salinity. Moreover, 8 parts per thousand salinity also increased plasma total protein and cholesterol levels and decreased glucose levels. These results indicated that the recommended range of lysine requirement under different salinity was 2 center dot 03-2 center dot 20 % (0 parts per thousand) and 2 center dot 20-2 center dot 41 % (8 parts per thousand) and 8 parts per thousand salinity resulted in higher lysine requirements due to changes in the related nutrient metabolism, which might provide useful information for designing more effective feed formulations for GIFT cultured in different salinity environment.

Automated summary

This 62-day research evaluated the effects of dietary lysine levels and salinity on the growth performance and nutrition metabolism of genetically improved farmed tilapia juveniles. The results showed that lysine supplementation and appropriate salinity levels improved the growth rate and weight gain, while also affecting nutrient metabolism. The study provides useful information for designing effective feed formulations for tilapia cultured in different salinity environments.