Humoral immune factors modulated by copper and chitosan in healthy or parasitised carp (Cyprinus carpio L.) by Ptychobothrium sp. (Cestoda).

As an environmental protection point of view, the potential toxicity of chitosan on aquatic animal health, alone or associated with copper must be investigated. Fish possess defence mechanisms to counteract the impact of toxics. The non-cellular and non-specific immune defences (total immunoglobulin, ceruloplasmin, lysozyme and potential killing activity of phagocytic cells) can be modulated by the potential environmental pollutants but also by natural stimulants such as bacteria, viruses or parasites. In this study, we investigate the potential toxicity of copper (0.1 and 0.25 mg/L) or chitosan (75 and 150 mg/L) and the combination copper and chitosan (0.1 and 75 mg/L, respectively) on two groups of carp: healthy or parasitised by Ptychobothrium sp. Fish exposed to water-soluble chitosan for 96 h had significantly high levels of natural antibodies in plasma. Moreover, activities of lysozyme and ceruloplasmin were also increased in plasma after the same treatment. The exposition of fish to copper have shown apparently contradictory effects on the immune parameters measured but, significant increase of this bacteriolytic activity was observed, particularly in head kidney after 4 days of treatment of fish with copper. The two products may induce separately an acute, short and local inflammatory acute phase response by stimulating some components of the innate immune response of healthy fish. The mixture seems to reduce the impact of the each product due to the physical and chemical properties of chitosan to complex with copper. The responses of humoral immune factors of treated carp was modulated by the presence of the parasite, as shown by the high elevation of lysozyme activity observed in parasitised carps after exposition to copper and by increases in natural antibodies levels observed in parasitised carp treated with the copper-chitosan mixture. This could indicate an additive effect on the stress response mediated by parasite. It occurred a greater stress response in the parasitised group than healthy group exposed to the same treatment evoking an additive effect. So, it is important to specify the health status of organisms to understand responses of immunological markers in fish. Copyright 2004 Elsevier B.V.