The gene expression of the trypsinogen and pepsinogen and activity of trypsin and pepsin in Indian walking catfish (Clarias magur) were investigated during the larval period to study the development of the digestive system. To this end, cDNA encoding the partial trypsinogen and pepsinogen were cloned and sequenced. Subsequently, the mRNA expression of genes was evaluated by quantitative polymerase chain reaction (qRT-PCR) along with the estimation of the activity of trypsin and pepsin. The mRNA expression pattern of trypsin appeared on 3rd-day post-hatching (dph) with a peak at 9 dph and 22 dph, while mRNAs of pepsin although detected at 4 dph but exhibited the significantly (P < 0.05) higher expression at 19 and 22 dph. The specific activity of trypsin increased from 11 dph onwards up to 16 dph. Similarly, the specific activity of pepsin enzyme showed a sudden increase from 13 to 19 dph. Based on these results, we suggest that the weaning time for C. magur larvae could be after 16 dph, as the activities were significantly increased after this stage which marks the functional development of the exocrine pancreas and stomach.
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