Effect of different protein sources on protease activity of northern pike, Esox lucius Linneaus 1758, juvenile

The aim of the study is to determine the inhibitory effect of different protein sources on protease activity of Northern pike, E. Lucius, during larval ontogeny. For this purpose, Northern pike were fed from yolk sac absorption until 21 days after hatching (DAH). At that point, larvae were sampled on 7, 14 and 21 DAH days and the activity of enzyme was analyzed in vitro. In the study, two different fish meal, chicken meal, krill meal, corn gluten, soybean protein concentrate, soybean meal and dried distillers grains with solubles were tested. Fish meal-I showed the lowest effect (7.53 %) on 7 DAH larvae. Moreover, chicken meal has the highest inhibitory effect on the proteases in the first week (68.27%). In the following period (DAH 14), although the inhibition ratio dramatically increased in all ingredients, fish meal-I has still the lowest effect on proteolytic activity (55.66%). In the same period, the highest effect was obtained from krill (82.28 %) and chicken meals (86.73 %), respectively. Then, there was no statistical difference between fish meal-I, fish meal-II and corn gluten in the 21 DAH and relatively lower than the others (p>0.05). Additionally, chicken meal again has the highest effect on juveniles with the ratio 89.27 %. As a result, the increase of proteolytic activity was notably increased in 7-14-21 DAH, however, it is concluded that feeding larvae and juveniles with live prey is still suggested to get better result for such a carnivorous species culture.