Effects of vitamin D supplementation under different salinities on hybrid red tilapia growth performance, hormonal profile and growth genes expression

This study investigated the effects of salinity and vitamin D (VD) supplementation on the physiological and molecular responses of red tilapia hybrid juvenile. The research comprehensively examined growth performance, hormonal profiles, and gene expression under different experimental conditions. Growth performance analysis revealed significant improvements with increasing salinity levels and VD supplementation. The highest growth parameters were observed at 30 ppt salinity with vitamin D3 supplementation, including peak final weight (42.04 g), maximum average daily gain (0.467 g), and optimal feed conversion ratio (0.927-0.967). Survival rates consistently improved, reaching 84.33% under optimal conditions. Hormonal parameters demonstrated notable modulation, with growth hormone (GH) levels showing marked increases, particularly at 15-30 ppt salinity. Adrenocorticotropic hormone (ACTH) remained relatively stable across treatments, suggesting minimal stress response. Molecular analysis of gene expression revealed complex interactions between salinity and VD. The growth hormone (GH) gene showed significant upregulation, particularly at 30 ppt salinity with VD supplementation. The insulin-like growth factor II (IGF-II) gene expression exhibited a non-linear response, with substantial upregulation at 0 ppt salinity and downregulation at 30 ppt salinity. These findings highlight the intricate physiological adaptations and the role of vitamin D in juveniles of red tilapia hybrid under different salinity levels, Therefore, it is advisable to use 0.8 mg of VD followed by 0.4 mg under different salinity levels to enhance the growth performance, feed utilization, GH level, and expression of GH and IGF-II genes. Additionally, culturing fish at 30 ppt salinity followed by 15 ppt appears to improve overall performance compared to freshwater culture.