Determination of optimum dietary protein level for juvenile walleye pollock, Gadus chalcogrammus Pallas 1811

An 8-week feeding trial was conducted to investigate the effects of dietary protein level on growth performance, feed utilization, body composition, plasma chemistry and antioxidant parameters of juvenile walleye pollock (Gadus chalcogrammus ). Two-hundred and forty juvenile pollock, averaging 4.5 g, were randomly distributed between 12 400-L flow-through circular tanks (20 fish per tank). Four experimental diets with increased crude protein levels (40, 45, 50, and 55 %) were formulated, and referred to as the P40, P45, P50, and P55 diets, respectively. Each diet was assigned to three tanks and the fish were hand-fed to satiation twice daily. At the end of feeding trial, weight gain and specific growth rate increased with increasing dietary protein up to 50 %, and then decreased with further increase in dietary protein. The feed intake of the fish fed the lowest protein diet (P40) was greater than those of fish fed the higher protein diets (P45, P50 and P55). The feed efficiency was the lowest in the P40-fed fish. The protein retention tended to increase with dietary protein, from P40 to P45, and then decline when the dietary protein level was further increased to P55. The whole-body composition, except for the crude protein content, was not affected by the dietary protein content. Antioxidant response was also not affected by the dietary protein content. In conclusion, based on a second-order polynomial regression analysis of weight gain, the optimum dietary protein level for juvenile pollock was estimated to be 48.2%.