Histopathological changes induced by environmental stress in common carp, Japanese coloured carp, European eel, and African catfish.

Histopathological changes caused by stress during catching and transport were examined in four fish species, the common carp (Cyprinus carpio), the Japanese coloured carp (koi, the coloured variant of the Asian carp, Cyprinus carpio haematopterus), the European eel (Anguilla anguilla), and the African catfish (Clarias gariepinus). In all species, the goblet cells of the gills and skin were decreased in number and slight detachment of the epithelium of the secondary gill lamellae was seen. Loss of goblet cells and detachment of the columnar epithelial cells were found in the intestinal mucosa of common carp and coloured carp. It is supposed that these lesions may affect ion transport and respiration in the gills and disturb normal intestinal function, thus serving as a starting point for different diseases.