Effects of Fish Meal Replacement with Composite Mixture of Soybean Protein Hydrolysates and Other Plant Proteins on Growth Performance, Antioxidant Capacity, and Target of Rapamycin Pathway in Largemouth Bass

Abstract A feeding trial was conducted to evaluate the effect of fish meal replacement with a composite mixture of soybean protein hydrolysates and other plant proteins on growth performance, antioxidant capacity, and target of rapamycin pathway in Largemouth Bass Micropterus salmoides. Triplicate groups of Largemouth Bass were fed the diet formulated with 40% (FM40; control), 35% (FM35), 30% (FM30), or 25% (FM25) fish meal for 10 weeks. The results revealed that the best growth performance was achieved in the FM35 group, while a negative effect on growth was observed in the FM25 group. The feed intake of the FM30 and FM25 groups was significantly lower than the other two groups, while no significant difference was observed in feed efficiency ratio and protein efficiency ratio. No statistical difference was observed in the activity of serum alanine transaminase and aspartate transaminase with the replacement of fish meal. However, the replacement of fish meal with composite plant protein significantly reduced hepatic malondialdehyde content, and a significant improvement in total antioxidant capacity was observed in the FM35 group. Gene expression analysis revealed that the expression of amino acid transporter LAT1 was significantly elevated in the FM35 group, while no significant difference was observed in the LAT2 expression among different treatments. No significant difference was observed in the expression of target of rapamycin among treatments. However, the expression of ribosomal protein S6 in the FM35 and FM30 groups was significantly higher than in the other two groups, while the replacement of fish meal significantly decreased the expression of eukaryotic initiation factor 4EBP1. In summary, the composite mixture of soybean protein hydrolysates and other plant proteins can reduce the use of fish meal from 40% to 35%.