Optimization of weaning age for striped murrel (Channa striata) based on expression and activity of proteases

The pattern of gene expression and the activity of three proteases - trypsin, chymotrypsin, and pepsin - were investigated from yolk sac stage to 35 days post hatching (dph) in larvae and juveniles of striped murrel (Channa striata), a high-value fish species with a great potential for aquaculture. The mRNA expression level of trypsin increased from 3 dph onwards and concurrently with absorption of the yolk sac, peaking at 12 dph and 25 dph (p < 0.05). Chymotrypsin expression peaked at 21 dph. In pepsin, mRNA levels were not detectable from hatching to 3 dph but increased significantly at 25 dph (p < 0.05). Maximum specific activity of trypsin was observed at 18 dph, while chymotrypsin showed significantly higher (p<0.05) activity at 21 dph. Specific activity of pepsin increased from 18 dph onwards and peaked at 30 dph. These patterns suggest that larvae/juveniles of C. striata are best weaned between 18 dph and 25 dph to coincide with functional development of the exocrine pancreas and stomach.