Reduction of stress response in carp,Cyprinus carpioL., held under deteriorating environmental conditions, by oral administration of bovine lactoferrin

Abstract

Bovine lactoferrin (LF) was evaluated for its ability to suppress stress reactions in carp, Cyprinus carpio L., held under deteriorating environmental conditions. Three test diets containing different levels of LF (0.01, 0.1 and 1%) were fed at 2% of fish body weight per day, i.e. LF at 2, 20 and 200 mg kg(-1) body weight day(-1) was administered orally to carp for 14 days at 20 °C. In the fish reared at a density of 2 individuals 10 l(-1) , plasma cortisol, adrenaline and noradrenaline decreased in the groups fed with 0.1 and 1% LF content diets. In the fish held at a density of 10 individuals 10 l(-1) for 3 days, plasma cortisol, adrenaline, noradrenaline, dopamine and glucose were higher than those at 2 individuals 10 l(-1) in both the control and LF-treated groups. The extent to which these parameters were elevated in the fish held at the same density was reduced with increasing LF content of the diet. Twenty-four hours after exposure to hypoxic conditions (dissolved oxygen level, 2.5 mg l(-1) ), haemoglobin, haematocrit, plasma cortisol, adrenaline, noradrenaline and dopamine increased significantly in all groups. The responses of hypoxic fish fed with 0.1 and 1% LF diets for 14 days were smaller than those of the controls. These results suggest that LF has an ability to reduce the stress response of carp held under deteriorating environmental conditions.