Proteolytic enzyme activity of juvenile Asian sea bass, Lates calcarifer (Bloch), is increased with protein intake

The effect of high dietary protein intake on proteolytic enzyme activity of feeding juvenile Asian sea bass, Lates calcarifer (Bloch) was studied. Ninety fish [mean body weight +/- standard error (SE) 304.62 +/- 34.84 g] were randomly assigned to two dietary treatments, each with three replicates. In treatment 1, fish were fed by-catch (Thunnus albacares ) and in treatment 2, a formulated diet containing 50% protein. Proteolytic enzyme activity was determined in pyloric caecae and intestine at day 0, 7, 15, and 30. Initial proteolytic enzyme activity in sea bass ranged from 174 to 232 azocasein units (U-AC. ) per mg of protein. After 7 days there was no significant difference in proteolytic enzyme activity of fish fed the two diets. However, a marked increase was observed in fish fed the formulated diet at day 15. After 30 days, the proteolytic enzyme activity in fish fed the formulated diet was threefold higher than that in fish fed the by-catch diet. Fish fed the formulated diet had significantly higher total protein intake at day 7 than did fish fed by-catch. Thereafter, a twofold weekly increase in the total protein intake was observed in both fish fed the by-catch and formulated diets until day 30. These results suggest that a high dietary protein intake induces increased proteolytic enzyme activity in Asian sea bass.