Assessment on the effects of different lipid sources in juvenile largemouth bass (Micropterus salmoides) diets

To evaluate the effects of substituting soybean oil (SO) with soy lecithin (SL) and specialty lipid (CL) on the growth, body composition, and glucose-lipid metabolism of juvenile largemouth bass (Micropterus salmoides). The CL is a composite lipid source formulated by mixing coconut oil, linseed oil, soy lecithin oil, and palm oil in a ratio of 2:2:3:3, with the addition of antioxidants and emulsifiers as fillers. A total of six experimental groups were established: an iso-nitrogenous and iso-lipidic soybean oil (SO) (control group), a 1% soy lecithin supplementation group (1% SL), a 2% soy lecithin supplementation group (2% SL), a 2.5% specialty lipid supplementation group (2.5% CL), a 5% specialty lipid supplementation group (5% CL), and a 7.5% specialty lipid supplementation group (7.5% CL). After a 10-week feeding trial (initial body weight: 12.64 ± 0.02 g), the results showed that final body weight (FBW), weight gain rate (WGR), and specific growth rate (SGR) in the 2.5% CL and 5% CL groups were significantly higher than those in the SO group. The 5% CL group exhibited the lowest feed conversion ratio (FCR) numerically, though no significant differences were observed among groups. Whole-body crude lipid content was significantly reduced in the 7.5% CL. Compared to other groups, the 5% CL and 7.5% CL showed significantly increased levels of saturated fatty acid (SFA), docosahexaenoic acid (DHA), and n-3/n-6 polyunsaturated fatty acid (PUFA), while PUFA levels markedly decreased. Compared to the control, the 7.5% CL showed significant decreases in plasma serum albumin (ALB), total protein (TP), total cholesterol (TC), triglyceride (TG), high-density lipoprotein (HDL), and low-density lipoprotein (LDL). Regarding lipid metabolism gene expression, the 5% CL exhibited a significantly lower expression level of the peroxisome proliferator-activated receptor-γ (pparγ) in contrast to SO. The expression levels of peroxisome proliferators-activated receptor-α (pparα) were significantly upregulated in the 5% CL and 7.5% CL compared to other groups. Furthermore, the carnitine palmitoyltransferase (cpt1) expression level in the 5% CL was significantly higher than in all other groups. In conclusion, CL enhanced growth performance, effectively reduced whole-body lipid deposition, improved fatty acid composition, and promoted lipid metabolism in juvenile largemouth bass, without adversely affecting liver function. Based on the comprehensive results, the recommended optimal inclusion level for specialty lipid was 5%.