Dietary enzymatic rice protein and enzymatic fish paste affect the growth, muscle development and quality traits of juvenile channel catfish (Ictalurus punctatus)

Fishmeal serves as the major protein for aquafeeds, whose limitations are observed owing to its high price and dependence on imports. Enzymatic rice protein (RP) and enzymatic fish paste (FP) were evaluated as potential alternatives to fishmeal in industrial aquafeeds. A basal fishmeal diet (10% fishmeal) was used as a control (FM), then three diets were formulated with fishmeal replaced by RP in amounts of 2.5% (RP2.5), 5.0% (RP5.0) and 7.5% (RP7.5). To further reduce dietary fishmeal, two diets based on the RP5.0 (5.0% fishmeal) were formulated, in which FP replaced fishmeal at levels of 2.5% (FP2.5) and 5.0% (FP5.0). The six diets were fed thrice daily to channel catfish (Ictalurus punctatus, initial mean weight 6.50 g) for eight weeks to evaluate growth and muscle quality. The weight gain rate (WGR) of fish was highest in RP2.5 group and lowest in RP7.5 group (P < 0.05). No significant differences in WGR were observed among the RP5.0, FP2.5, FP5.0 and FM groups (P > 0.05). Further, the RP7.5 diet significantly reduced total protein content of muscle than FM diet. Conversely, dietary FP (FP2.5, FP5.0) increased total protein and crude lipid content, and significantly improved muscle textures (hardness, gumminess, and chewiness), coupled with a significant increase in transverse section area of myofibers (AMF). Real-time qPCR showed that FP supplement significantly up-regulated muscle myod mRNA and down-regulated mstn mRNA, thereby regulating the myofiber development, which in turn affected muscle texture. Conversely, RP7.5 diet significantly down-regulated myod mRNA and resulted in a decrease in density of myofibers (DMF). Further, RP2.5 and RP5.0 diets significantly increased catalase (CAT) activity of muscle. FP supplement significantly up-regulated muscle gsh-px4b mRNA and increased the activities of CAT and glutathione peroxidase (GSH-PX). In summary, replacing 2.5% fishmeal with RP could improve growth performance, while growth was reduced when it reached to 7.5%, possibly by inhibiting muscle development. Notably, fishmeal could be completely replaced by a mixture of 5.0% FP and 5.0% RP, contributing to maintaining growth as well as promoting muscle development and antioxidant properties.