Histopathological changes in fish gills infected with myxosporidian parasites of the genus Henneguya

Tissue reaction to invasion by two Henneguya species was studied in gills of three species of fish. Henneguya psorospermica and Henneguya creplini develop in secondary lamellar arterioles in perch ( perca fluviatilis ) and ruff ( Acerina cernua). In pike ( Esox lucius), H. psorospermica develops in the artery. During the growth of the vegetative stage, the gill tissue may undergo local atrophy or hyperplasia of the epithelium and displacement and disfiguration of the lamellae. After the myxosporidian cyst, surrounded by a host tissue capsule has reached maturity and contains fully-formed spores, an inflammatory reaction may set in which reduces the cyst to granulomatous tissue. This inflammatory process is essentially of the same type as that observed in mammals. There is evidence that inflammatory responses are of regular occurrence in the final stages of most myxosporidian infections. Transfer from low to room temperature provokes a rapid elimination of the cysts by granulomatous inflammation.