[Necrotic processes in the gill tissue of carp caused by changes in the aquatic environment]

Histological findings show that various pathogenic processes are involved in the cases of clinically detected branchionecrosis. The changes in gills occurring at toxic branchionecrosis are a necrobiotic process in their nature; in gill lamellae this process manifests itself as a swelling of the respiratory epithelium and as dilation of lamellar sinuses, and in stratified epithelium of gill arch and filaments it takes on the form of the hypertrophy and hyperplasia of epithelial cells. In severe cases the swollen epithelium forms deposits filling up also the interlamellar space. Toxic branchionecrosis is a term referring to a disease when the pathological processes are caused by ammonia intoxication and autointoxication, the main role being played by pH value. At experimental ammonia intoxication the changes in gills are about the same as in toxic branchionecrosis but the symptoms are not so pronounced. Changes characteristic of spherosporosis involve severe necrotic processes in the respiratory epithelium as well as in the stratified epithelium of gills, and the epithelium harbours different developmental stages of spherospores. The spherospores are easily detected when stained with alcian blue at pH 2.5. The changes in the gills of carp naturally invaded by spherospores with additional ammonia intoxication correspond to findings characteristic of toxic branchionecrosis: degeneration of stratified and respiratory epithelium of gills combined with necrotic changes caused by the developmental stages of spherospores. When water is highly oxygenated with chlorinated lime, large cells with eosinophilic granules severely multiply mainly in the stratified epithelium of gills; this process is considered as an inflammatory process. Parasitic invasions by Trichodina and Chilodonella induce local inflammatory reactions with the swelling of the respiratory epithelium.