Alterations of club cell activity in epidermis of common carp, Cyprinus carpio (Actinopterygii: Cypriniformes: Cyprinidae), due to infection by Ichthyophthirius multifiliis (Protista: Ciliophora)

Background. The abundance of club cells in epidermal tissue of fishes in the superorder Ostariophysi is a poorly understood phenomenon. Previous results have suggested that epidermal club cells have a generic role in response to injury and that they display intense phagocytotic activity, having an anti-parasitic function in the host. Earlier works suggested that club cells are usually located in the middle of the epidermis and that they do not communicate with the epidermal surface or do it only when the epidermis has been ruptured by predation. The presently reported study focused on the alterations of club cell activity in carp epidermis induced by ectoparasite, Ichthyophthirius multifiliis. We hoped that our observations would help to understand the function(s) of these cells. Materials and methods. This study was based on 200 four-month old common carp, Cyprinus carpio L., with mean body weight of 65 ± 5 g. The fish were experimentally infected with theronts of Ichthyophthirius multifiliis. In sequential days post infection, samples of fins and body skin were collected for histological and histochemical examination. The correlation between club cell densities and mucous cell densities was analysed using Pearson correlation analyses. Results. A local reduction of mucous cells occurred after theront invasion-induced proliferation, and increased club cell density around the parasite during the growth of trophonts. After parasites left the skin due to salt-water treatment, a decrease in the number of club cells was detected. During reinvasion the decrease in parasite activity in areas of club cells proliferation was not noted. It was found that giant mature club cells were opened on the surface. Conclusion. Club cells have no anti-parasitic function against I. multifiliis and these mature cells released their viscous secretion into water. The high density of club cells in the epidermis compensates an overall low density or absence of mucous cells. As it can be hardly concluded that the function of club cells is phagocytic removal of cell debris, an integrated research on mucosal immune mechanisms, as well as studies on epidermal tissue responses on product(s) released by club cells (“alarm substance cells”) should be carried out in the future.