Abstract
In a previous paper, the authors reported that the susceptibilities of Japanese eel (Anguilla japonica) to Edwardsiella tarda and Pseudomonas anguilliseptica were increased by exposure to sublethal concentrations of copper (100 or 250 μg-Cu/l) for 24 or 48 hours, and this was interpreted as a tertiary response to stress. In the present study, primary and secondary responses to stress caused by copper exposure were investigated.
The apparent increase of corticosteroids was observed in eels exposed to copper for 12 hours. The numbers of lymphocytes and granulocytes in the 24 hour-exposed eels decreased to one third of those of control fish. It was also demonstrated by an in vitro test that phagocytic rate of leucocytes in the blood of the stressed eels lowered against E. tarda but not against Vibrio anguillarum.
From these results, the increased susceptibility to the pathogens is interpreted as due to lowered phagocytosis.
