THE EFFECT OF DIETARY CARBOHYDRATE ON THE STRESS RESPONSE IN COD (GADUS-MORHUA)

150 cod (mean weight = 440 g) were divided into two groups and fed diets with or without carbohydrate for 60 days. No differences were found in total growth during the feeding period. Both fish groups were then stressed by handling and transported for 2 h. Five fish from each dietary group were collected for analysis at different time intervals up to 96 h. In terms of serum cortisol increase, the stress response was significant in both dietary groups and reached a maximum after half an hour. No response was found in blood hematocrit or in blood hemoglobin at any sampling time. The plasma glucose levels in resting fish reflected the dietary levels of carbohydrate. The plasma glucose response was also significantly more affected by stress in the carbohydrate-eating fish than in the fish on a carbohydrate-free diet. Blood lactate did not reflect the diet composition, while a significant increase was seen in both groups after 1.5 h of recovery. No change in muscle lactate was measured as a response to stress, but significantly higher muscle lactate levels were measured in the fish without dietary carbohydrate. Neither white muscle nor hepatic glycogen levels were affected by the diet, but a significant increase was seen in both organs in the fish on a carbohydrate feed after 3 h of recovery.