Effects of Replacing Fishmeal with Enzymatically Hydrolyzed Pork Bone Meal (EHPBM) on Growth, Antioxidant Capacity, and Nutritional Metabolism in Micropterus salmoides

In this 8-week feeding trial, we systematically investigated the effects of replacing fishmeal with enzymatically hydrolyzed pork bone meal (EHPBM) at graded inclusion levels (EHPBM0, EHPBM20, EHPBM50, and EHPBM100) in largemouth bass (<i>Micropterus salmoides</i>). The results showed that the EHPBM50 group maintained growth performance comparable to the fishmeal-based control, whereas higher replacement levels led to significant metabolic disturbances. Specifically, the EHPBM100 group exhibited marked reductions in final body weight (FBW), weight gain rate (WGR), and specific growth rate (SGR), along with an elevated feed conversion ratio (FCR). Serum biochemical markers-alanine aminotransferase (ALT) and aspartate aminotransferase (AST)-were significantly decreased in a dose-dependent manner under EHPBM50 and EHPBM100 substitution. Regarding whole-body composition, ash content was significantly lower in the EHPBM50 group, while no significant differences were observed in other metrics compared to the control. Furthermore, dietary EHPBM inclusion enhanced systemic antioxidant capacity. All EHPBM substitution groups showed significantly increased superoxide dismutase (SOD) and catalase (CAT) activities, along with significantly reduced malondialdehyde (MDA) levels. In key metabolic pathways, compared with the EHPBM0 group, the expression of <i>mtor</i> and <i>rps6k</i> genes was significantly up-regulated in the EHPBM50 group, while that of <i>g6pase</i>, <i>fbp1</i>, and <i>cpt1</i> genes was significantly down-regulated. Intestinal integrity markers (<i>occludin</i>, <i>zo-1</i>) and nutrient transporters (<i>pept1</i>, <i>lat1</i>) remained largely unaffected except in the EHPBM100 group, indicating the species' tolerance to partial fishmeal replacement. In summary, these findings demonstrate that EHPBM can effectively replace up to 50% of fishmeal in largemouth bass feed without compromising growth performance or nutrient utilization, while significantly enhancing antioxidant capacity.