Effects of Soybean Meal on New Muscle Generation and Enzyme Activities in Nile tilapia, Oreochromis niloticus

Abstract

The use of fishmeal (FM) substitute ingredients in aquafeeds has lately gained attention due to the rising cost of FM associated with the rapid expansion of aquaculture. This study evaluated the effects of replacing FM with soybean meal (SBM) on new muscle generation and enzymatic activities of Nile tilapia, Oreochromis niloticus. Five experimental diets were formulated by replacing fishmeal with SBM at 0% (SBM0), 25% (SBM25), 50% (SBM50), 75% (SBM75), and 100% (SBM100). Nile tilapia (initial weight: 6.60 ± 0.13 g and length: 5.42 ± 0.17 cm) were randomly assigned to five treatment groups (each having three replications) and fed to apparent satiation for 180 days. Muscle histology was assessed by determining muscle fiber density (mm-2 ) and diameter (µm). Additionally, creatine kinase (CK), alkaline phosphatase (ALP), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) activities were measured from the dorsal muscle tissues. Fish fed the SBM0 and SBM25 diets exhibited significantly higher muscle fiber density and smaller muscle fiber diameter than those fed the SBM100 diet (p < 0.05). Whereas muscle fiber diameter increased progressively with increasing dietary SBM inclusion. Histological observations confirmed that lower SBM inclusion maintained numerous small muscle fibers characteristic of hyperplastic growth. Higher SBM inclusion (SBM75 and SBM100) resulted in fewer but larger muscle fibers, indicating a shift towards hypertrophic growth. CK and ALP activities were not significantly affected by dietary treatments (p > 0.05). However, AST and ALT activities were significantly (p > 0.05) reduced in fish fed the SBM75 and SBM100 diets, suggesting altered amino acid metabolism at higher SBM inclusion levels. These findings indicate that replacing fishmeal with SBM up to 50% maintains normal muscle development and metabolic functions, whereas higher replacement levels (≥ 75%) adversely affect muscle growth characteristics and metabolism. Therefore, partial replacement of fishmeal with soybean meal represents a suitable dietary strategy for Nile tilapia while supporting the sustainable use of alternative protein sources in aquaculture.