Effects of fishmeal replacement with composite mixture of shrimp hydrolysate and plant proteins on growth performance, feed utilization, and target of rapamycin pathway in largemouth bass, Micropterus salmoides

An 82 days' feeding trial was conducted to investigate the potentiality of fishmeal replacement with the composite mixture of shrimp hydrolysate and plant proteins in diets for largemouth bass. Triplicate groups of fish were fed the experimental diets with 45 (FM45, the control), 40 (FM40), 35 (FM35), 30 (FM30) and 25% (FM25) fishmeal twice daily. Results showed that the mixture of protein sources can reduce the use of fishmeal to 30% with obvious improvement of growth performance, whereas higher substitution level (FM25 group) inhibited growth slightly compared to the control group. The fishmeal replacement supported significantly higher apparent digestibility coefficients (ADC) of protein and amino acids compared to the control, which may be partly involved in the activation of amino acid-sensing target of rapamycin (TOR) pathway. Consistently, the replacement of fishmeal elevated the expression of TOR and ribosomal protein S6, but significantly decreased the expression of eukaryotic translation initiation factor 4E (eIF4E)-binding protein 1 (4E-BP1), and this confirmed the activation of TOR pathway induced by the fishmeal replacement in the present study. In summary, appropriate fishmeal replacement with composite mixture of shrimp hydrolysate and plant proteins can activate the TOR pathway and improve the growth performance of largemouth bass, and fishmeal content in the diets for largemouth bass can be reduced to 30% with the compound proteins.