Comparison of Physiological Responses to Plant-Protein- and Carbohydrate-Based Fishmeal Substitutes in Largemouth Bass (Micropterus salmoides)

Abstract

Simple Summary Fishmeal replacement has been a concern in aquaculture, and it is important for the sustainable development of aquaculture and marine ecology. The study investigated the physiological responses of Micropterus salmoides to fishmeal replaced by soybean meal (SM) versus α-starch (ST). The results revealed that dietary substitution with SM yielded superior growth outcomes within the 5–15% inclusion range relative to equal levels of ST. Notably, the adverse effects of SM exceeded those of ST when the substitution level reached 20%, owing to severe intestinal inflammatory responses. ST diets mainly reprogram hepatic lipid metabolism in fish and consequently induce fatty liver symptoms, whereas SM diets primarily damage the physical intestinal structure. Greater attention should be paid to the rational utilization of dietary carbohydrates, as appropriate carbohydrate supplementation (15%) can exert a prominent protein-sparing effect. These findings provide valuable information for the balanced application of plant protein and carbohydrate sources in the feed formulation of M. salmoides, which can mitigate the adverse physiological costs induced by different fishmeal replacement strategies.