Replacement of Supplemental Fish Oil by Linseed or Soybean Oil Reshapes Hepatic Lipid Metabolism Without Compromising Growth in Juvenile Chinese Soft-Shelled Turtle (Pelodiscus sinensis)

Reducing reliance on supplemental fish oil is central to sustainable aquaculture, but the molecular consequences of replacing it with vegetable oils remain poorly characterized in the juvenile Chinese soft-shelled turtle (Pelodiscus sinensis). We evaluated whether full substitution of the supplemental dietary fish oil (FO) with linseed oil (LO) or soybean oil (SO) compromises hepatic lipid metabolism in Pelodiscus sinensis. Three isonitrogenous and isolipidic diets, sharing identical fish meal and other ingredient bases and differing only in the supplemental lipid (4% FO, LO or SO), were fed to triplicate groups of juvenile turtles (initial body weight 55.0 ± 0.05 g) for 8 weeks. Growth performance, survival, feed conversion ratio, and serum biochemistry were unaffected. However, both vegetable oil diets altered tissue fatty acid composition, raising n-6 PUFA and lowering n-3 LC-PUFA and the n-3/n-6 ratio in liver and muscle (muscle EPA and DHA each decreased by approximately 40%); the SO group additionally exhibited elevated hepatic malondialdehyde, whereas hepatic lipid droplet area and lipid content did not differ significantly among groups. Liver transcriptomic profiling identified 262 (LO vs. FO) and 214 (SO vs. FO) differentially expressed genes, converging on lipid storage and bile acid metabolism. RT-qPCR confirmed the up-regulation of PLIN3, G0S2 and APOF and the down-regulation of CYP7A1. Over 8 weeks, replacement of supplemental FO maintained growth without overt impairment while altering tissue fatty acid profiles and the hepatic expression of key lipid metabolism genes.