Hyperthermal stress potentiates enhanced lipid utilisation in genetically improved farmed Tilapia, Oreochromis niloticus juveniles.

The present experiment evaluated whether dietary protein (P) or lipid (L) is preferred as an energy source by genetically improved farmed tilapia (GIFT) reared at high temperatures. A 60-day feeding trial was conducted at 28.3 °C and 33.3 °C, testing five diets with varying protein (34,36,38 %) and lipid (8,10,12 %) levels, viz., PL, PL, PL, PL, PL. Parameters assessed included growth, body composition, serum lipids, enzyme activities, fatty acid profiles, and PPAR-α mRNA expression. Results indicated that the fish fed optimum protein and highest lipid level (PL) showed significantly higher (P < 0.05) weight gain percent and thermal growth coefficient. Increasing dietary lipid content reduced whole-body lipid deposition and mobilised serum triglycerides and cholesterol at higher temperatures (HT). Hepatic malic enzyme activity decreased with rising temperature and lipid content, while lipoprotein lipase activity in muscle increased. The fatty acid composition altered substantially with the changes in rearing temperature and diets. Unsaturated fats were preferred as direct fuels for β-oxidation, wherein the PL groups preserved body (area %) EPA, DHA, and linolenic acid, especially at HT. The expression of PPAR-α, a lipolytic marker, was upregulated with increasing temperature and high dietary lipid content, peaking in PL groups. The study concludes that high-lipid diets (12 %) are metabolically superior to high-protein diets for GIFT tilapia at elevated temperatures, optimising growth, enhancing metabolic efficiency, and maintaining essential fatty acid profiles under hyperthermal stress.