Growth, fatty acid composition, and fillet quality of largemouth bass (Micropterus salmoides) fed soybean oil and cottonseed oil diets

A two-factor feeding trial evaluated the effects of soybean oil (SO) and cottonseed oil (CO), at 50 % or 100 % dietary lipid inclusion on growth, lipid metabolism, and fillet quality in largemouth bass (Micropterus salmoides). A total of 120 fish (51.66 ± 0.01 g) were assigned to four groups: SO50, CO50, SO100, CO100. All diets contained 30.2 % fishmeal, with approximately 0.8 % n-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA). SO diets had higher α-linolenic acid (ALA) level than CO. Growth performance was significantly affected by oil sources, with CO, particularly CO100, causing reduced final body weight (FBW), weight gain (WG) and specific growth rate (SGR), and higher feed conversation ratio (FCR). CO supplementation significantly reduced plasma triglycerides (TG), total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) and hepatic TG, corresponding with elevated adipose triglyceride lipase (atgl) expression and phosphorylated AMP-activated protein kinase (p-AMPK) levels. Fillet quality parameters also changed, with decreased water holding capacity (WHC), increased pH at 100 % vegetable oil inclusion, and improved textural properties (cohesiveness, gumminess, and chewiness) in CO diets. Although dietary ALA and desaturase gene expressions were higher in the SO groups, the n-3 LC-PUFA content in muscle and liver, as well as hepatic fatty acid desaturase (FADS) activities, did not differ significantly from those in the CO groups. In conclusion, the lack of ALA in CO, combined with limited n-3 LC-PUFA conversion capacity and the elevated lipid catabolism, particularly in the CO100 group, contributed to the inferior growth performance in largemouth bass.