Effects of enzymatically hydrolyzed chicken liver paste replacing fish meal on growth performance, glycolipid metabolism and muscle quality of Micropterus salmoides

Micropterus salmoides is an economically important carnivorous freshwater fish in China relying heavily on fishmeal for balanced nutrition. Global fishmeal supply shortage and soaring prices greatly raise breeding costs and hinder sustainable largemouth bass culture. Enzymatically hydrolyzed chicken liver paste, a low-cost livestock by-product rich in peptides, amino acids and attractants, serves a promising fishmeal substitute, yet relevant aquatic research remains scarce. Carnivorous M. salmoides has weak hepatic carbohydrate and lipid regulation; inappropriate dietary protein sources easily cause hepatic steatosis and deteriorated fillet texture. Dietary protein sources regulate mTOR-mediated protein anabolism and hepatic lipid metabolism, jointly determining fish growth, antioxidant status and meat quality. Therefore, this trial partially replaced fishmeal with graded levels of enzymatically hydrolyzed chicken liver paste, and investigated its effects on growth performance, hepatic glucolipid metabolism and fillet quality to determine its optimal replacement ratio for largemouth bass feeds. The application effect of EMCLP replacing fish meal was evaluated based on growth performance, biochemical indices, nutrient metabolism and muscle quality. Four isonitrogenous (crude protein 43%) and isolipidic (crude fat 15%) experimental diets were formulated by replacing 0%, 5%, 10% and 15% of fish meal with EMCLP. Juvenile largemouth bass with an initial body weight of (14.03±0.96) g was fed for 8 weeks. No significant differences were observed in final body weight, weight gain rate, specific growth rate, protein efficiency ratio, hepatosomatic index, viscerosomatic index, whole-body proximate composition, or muscle texture parameters (springiness, cohesiveness, and resilience) among all dietary groups. Compared with the fish meal group, EMCLP substitution enhanced fish feed intake, feed utilization, and systemic antioxidant capacity, upregulated the expression of genes related to muscle protein synthesis (e.g., akt, mtor, s6k1, s6, and 4ebp1), hepatic lipolysis (e.g., pparα, cpt1, and aco1), and hepatic glycolysis (e.g., glut2, gk, pk, and hk), and increased muscle crude protein content and textural properties including hardness and gumminess. Concurrently, the substitution reduced plasma glucose, triglycerides, and oxidative damage products; decreased hepatic triglycerides, malondialdehyde, and cholesterol contents; lowered muscle fat deposition; and suppressed the transcription of key genes involved in hepatic gluconeogenesis (e.g., pepck and g6pase) and lipogenesis (e.g., acc1 and fas). Most functional parameters exhibited a quadratic response to increasing replacement levels, with the 10% replacement group achieving the optimal comprehensive performance, as evidenced by peak values in muscle crude protein, chewing-related texture attributes, antioxidant capacity, and lipolysis-related indicators. Notably, the 15% replacement group maintained positive regulatory effects on muscle protein synthesis-related pathways. Dietary replacement of fish meal with up to 15% EMCLP did not compromise the growth performance of largemouth bass and promoted muscle protein synthesis. The 10% replacement level represented the optimal inclusion rate, improving feed intake efficiency, systemic antioxidant capacity, protein deposition, and muscle quality.