Dietary interaction of soybean oil and high starch impairs growth performance via metabolic-inflammatory dysregulation in Siberian sturgeon (Acipenser baerii).

Sturgeons, ancient fish and the source of caviar, are ecologically and economically vital in aquaculture. To enhance feed efficiency, the use of cost-effective non-protein ingredients such as soybean oil and starch has gained growing attention. This study investigated the effects of oil sources and starch levels on growth, lipid metabolism, and inflammation in Siberian sturgeon (Acipenser baerii). Four isonitrogenous and isolipidic diets were formulated: fish oil diet with low starch level (FOLS), soybean oil diet with low starch level (SOLS), fish oil diet with high starch level (FOHS), and soybean oil diet with high starch level (SOHS). A total of 240 fish (initial weight: 182.87 ± 0.24 g) were used in a 10-week feeding trial. They were randomly assigned to 12 tanks, with three replicates per diet. Results showed that oil source had no significant effect on growth performance (final body weight [BWf], weight gain rate [WGR], and specific growth rate [SGR], P > 0.05), but high starch significantly reduced final body weight, weight gain rate, and specific growth rate (P < 0.05). Both soybean oil and high starch independently increased feeding rate and feed conversion ratio (P < 0.05), with their interaction further reducing these two indexes (P < 0.05). High starch diets disrupted lipid metabolism. Specifically, they elevated hepatosomatic index, serum triglycerides (TG), total cholesterol (TC), and low-density lipoprotein cholesterol (P < 0.05), along with increased expression of hepatic genes related to fatty acid β-oxidation (pparα, P = 0.001). Soybean oil also promoted fatty acid β-oxidation (pparα and cpt1α, P < 0.05), and in combination with high starch, enhanced lipolysis (lpl, P = 0.042). Meanwhile, high starch upregulated the expression of pro-inflammatory gene (il1β, P = 0.020). The mRNA expression results indicated that the soybean oil-high starch combination further aggravated inflammation alongside enhanced fatty acid oxidation, ultimately impairing growth. A principal component analysis (PCA) analysis of the lipidome showed that the serum lipid profile was significantly affected by the oil source (P = 0.004). Seven metabolites were identified as commonly differentially abundant. Notably, phosphatidylethanolamine [PE (18:0_20:4) and PE (18:0_18:1)] and ceramide phosphate [CerP (d39:2)] were positively correlated with levels of TG, TC, and the expression of β-oxidation and inflammatory genes (P < 0.05), suggesting their potential key roles in lipid-inflammatory dysregulation. In conclusion, dietary soybean oil and high starch interact to modulate serum lipid molecules, enhance fatty acid β-oxidation and inflammation, reduce feed efficiency, and suppress growth. Therefore, careful regulation of starch levels is essential when substituting fish oil with soybean oil in sturgeon aquafeed formulations.