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

A 10-week feeding trial was conducted with juvenile large yellow croaker, <i>Larimichthys crocea</i>, 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 (<i>p</i> < 0.05) growth performance and feed efficiency. Additionally, significant increases (<i>p</i> < 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 <i>n</i>-6 polyunsaturated fatty acids (PUFA). Still, low in <i>n</i>-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 (<i>p</i> < 0.05) at 50% FO replacement, with upregulated lipid synthesis genes (<i>srebp1</i>, <i>fatp1</i>, <i>fas</i>, and <i>ppar-α</i>) leading to higher lipid accumulation. Inflammatory response gene expression is also significantly affected, showing amplified pro-inflammatory (<i>ifnγ</i>, <i>il-1β</i>, and <i>tnfα</i>) and decreased anti-inflammatory (<i>il-10</i>, <i>arg-1</i>, <i>tgfβ</i>) 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.