Effects of Fish Oil Replacement With Degossypolized Cottonseed Oil on Growth Performance, Proximate Composition, Lipid Metabolism, and Liver Function of Large Yellow Croaker (Larimichthys crocea) Juvenile

A 10-week feeding trial was conducted with juvenile large yellow croaker, Larimichthys crocea, to evaluate the effects of degossypolized cottonseed oil (DCSO) as a potential replacement for fish oil (FO). Five isonitrogenous (42% crude protein) and isolipidic (13% crude fat) diets were formulated where DCSO replaced FO at 0%, 25%, 50%, 75%, and 100% (DCSO0, DCSO25, DCSO50, DCSO75, and DCSO100) to determine their effects on growth performance, feed utilization and tissue lipid compositions of experimental fish. The initial body weight of the experimental fish was 8.28 ± 0.99 g. Results showed that substituting up to 50% of FO with DCSO does not significantly affect the fish’s survival rate (SR), growth performance, or proximate composition. However, exceeding a 50% replacement significantly decreases (p < 0.05) growth performance and feed efficiency. Additionally, significant increases (p < 0.05) in viscerosomatic index (VSI) and hepatosomatic index (HSI) are observed at higher DCSO inclusion levels. Fatty acid analysis shows that DCSO is rich in n-6 polyunsaturated fatty acids (PUFA). Still, low in n-3 PUFA alters fatty acid profiles in the liver and muscle, resulting in elevated total cholesterol (T-CHO), triglycerides (TG), and low-density lipoprotein cholesterol (LDL-C) levels, alongside increased activities of liver enzymes, indicating compromised liver function. While antioxidant enzyme levels remain stable, malondialdehyde (MDA) levels rise, suggesting elevated oxidative stress. Furthermore, lipase activity declines significantly (p < 0.05) at 50% FO replacement, with upregulated lipid synthesis genes (srebp1, fatp1, fas, and ppar-α) leading to higher lipid accumulation. Inflammatory response gene expression is also significantly affected, showing amplified pro-inflammatory (ifnγ, il-1β, and tnfα) and decreased anti-inflammatory (il-10, arg-1, tgfβ) cytokines at higher DCSO levels. In conclusion, while up to 50% replacement of FO with DCSO is acceptable, surpassing this threshold adversely affects growth, liver function, lipid metabolism, and inflammatory responses in juvenile large yellow croaker.