Growth variation and fin damage in Atlantic cod (Gadus morhua L.) fed at graded levels of feed restriction

Summary

Atlantic cod (initial weight 55, 250 and 450 g) were deprived of feed for I month or fed one of two diets differing in crude protein and lipid levels at rations corresponding to about 25, 50, 75 or 130% of group satiation for two months. The fish were individually weighed at the start, mid and end of the experiment and growth variation and fin damage were registered. The fin damage patterns differed between size groups; 55 g cod had most wounds on the dorsal fins whereas the pectoral fins were the most damaged in the 250 g fish. The incidence of damage in these groups was high and increased significantly when feeding was restricted. In the 450 g cod there was little fin damage and the incidence did not seem to depend on diet treatment. In the 55 and 250 g cod groups, fast growing fish had lower incidence of fin damage than fish that grew slowly, suggesting that the fish that received most aggression were prevented from feeding. However, a similar trend was registered in non-fed fish, showing that the recipients of aggression also suffered other disadvantages. The variation in individual growth rates increased when feeding was restricted and the distribution was differently skewed depending on feeding level. The data provide evidence that competition is an important factor limiting growth of individual cod held in groups in culture. (c) 2006 Elsevier B.V All rights reserved.