Evaluating soybean protein concentrate hydrolysate as a fishmeal substitute in the diet for mandarin fish (Siniperca chuatsi): Based on growth, intestinal health, flesh quality and nutrient metabolism

The present experiment investigated the effects of soybean protein concentrated hydrolysate (SPCH) replacing fishmeal (FM) on the growth performance, intestinal health, flesh quality, and nutrient metabolism of mandarin fish (Siniperca chuatsi). Five isonitrogenous and isolipidic diets were designed with different levels of dietary fishmeal substituted with SPCH at 0 (FM55), 18.70% (FM45), 37.16% (FM35), 55.40% (FM25), and 73.41% (FM15), respectively. Each diet was fed to three replicate groups of mandarin fish (a total of 450 fish, 37.18 ± 0.01 g) twice daily for 8 consecutive weeks, with 30 individuals per tank. The results showed that when the replacement level of SPCH did not exceed 37.16%, no significant effects on the growth of mandarin fish were observed (P > 0.05). Histological examination showed significantly enhanced hepatic lipid accumulation, while the mid-intestinal villus length and muscularis thickness reached their maximum in the FM35 group (P < 0.05). At the molecular level, SPCH modulated amino acid transport, as evidenced by upregulated expression of key transporter genes (lat1 and snat2) (P < 0.05). Meanwhile, SPCH substitution influenced the tor pathway in muscle tissue, as evidenced by the upregulation of related genes (akt1, tor, s6k, and s6) (P < 0.05). However, SPCH supplementation linearly upregulated hepatic lipogenic genes (srebp1, dgat1, acc1, acc2, and fas) while downregulating lipid catabolism genes (pparα, aco, and atgl) in a linear manner (P < 0.05). Additionally, when SPCH replacement exceeded 37.16%, mid-intestinal expression of inflammation-related genes (rela, mapk13, mapk14, and 5lox) was significantly upregulated (P < 0.05). Furthermore, as the replacement level of SPCH increased, muscle hardness, adhesiveness, springiness, chewiness, resilience, and shear force linearly decreased (P < 0.05), while gumminess linearly increased (P < 0.001). In summary, the study demonstrated that the inclusion of SPCH could effectively reduce the dietary fishmeal content from 55% to 35% without significantly compromising the growth performance, intestinal health, or overall quality of mandarin fish.