Dietary lipid requirements of larval genetically improved farmed tilapia, Oreochromis niloticus (L.), and effects on growth performance, expression of digestive enzyme genes, and immune response

The present study was performed to investigate the effects of dietary lipid level on growth performance, antioxidant defense, and mRNA levels of digestive enzymes and immune genes in larval genetically improved farmed tilapia (Oreochromis niloticus). The results show that larvae fed lipid levels of 4–11.5% had greater weight gain (WG), feed efficiency, protein efficiency ratio and survival than larvae fed the other dietary lipid levels (P 0.05) but lipid contents increased as dietary lipid level was increased. The 8% and 11.5% dietary lipid levels had stimulatory effects on trypsin mRNA level compared with those of larvae fed the 15% and 18.5% lipid diets. Intestinal and liver amylase mRNA levels decreased in larvae fed the 18.5% lipid diet, following the decrease in dietary starch. Analysis of the secondary curve equation for WG indicated that the optimal dietary lipid level in larval tilapia was 8.56%. In addition, the 4–11.5% lipid levels improved superoxide dismutase and glutathione peroxidase activities and increased mRNA levels of heat shock protein70, hepcidin antimicrobial peptide‐1, and C‐type lysozyme in the liver of larvae (P