Blended Oil With an Optimized Fatty Acid Profile Improves Fish Meal Substitution Efficacy in Carnivorous Teleost...

Several factors are known to affect the substitution of fish meal (FM) in aquafeeds, yet the influence of dietary fatty acid (FA) composition remains unclear. To investigate this, fish oil (FO), an FA-optimized blended oil (BO1) designed to meet the essential FA (EFA) requirements of largemouth bass (Micropterus salmoides), and a blend rich in n-6 polyunsaturated FAs (PUFAs) (BO2, a 2:3 mixture of FO and soybean oil) were used as dietary lipid sources. Three isoproteic (50%) and isolipidic (9%) diets with distinct FA profiles were formulated at either 24% (24FO, 24BO1, and 24BO2) or 16% (16FO, 16BO1, and 16BO2) FM inclusion levels. Juvenile fish (initial weight about 12.50 g) were fed the diets for 10 weeks. Results showed no significant differences in growth performance among the 24% FM groups. At the 16% FM level, the 16BO1 group exhibited growth comparable to the 16FO group and achieved significantly higher final body weight (FBW), weight gain rate (WGR), and specific growth rate (SGR) than the 16BO2 group (p < 0.05). Moreover, compared to 16BO2, the 16BO1 group demonstrated improved lipid metabolism (indicated by reduced hepatosomatic index [HSI], viscerosomatic index [VSI], triglycerides [TGs], nonesterified FAs [NEFAs], and blood urea nitrogen [BUN]), enhanced protein synthesis (reflected in increased total amino acids [TAAs], alanine transaminase [ALT], and aspartate transaminase [AST]), elevated antioxidant capacity (total antioxidant capacity [T-AOC] and catalase [CAT]), and upregulated mRNA expression of genes related to lipid oxidation (pparα, atgl, and acsl4) and protein synthesis (akt2 and eif4g). These findings demonstrate that optimizing dietary FA composition enhances FM substitution efficacy by promoting lipid-based energy supply, improving protein synthesis, and strengthening antioxidant responses. This study is the first to reveal that dietary FA profiles modulate FM replacement efficiency in aquatic feeds, providing new insights and viable strategy for developing low-FM diets to promote sustainable largemouth bass aquaculture.