Gonadal impairment in roach Rutilus rutilus from Finnish coastal areas of the northern Baltic Sea

Abstract

Gonadal impairment in roach Rutilus rutilus from Finnish coastal waters was studied during 1987-1995. The disease was observed in high prevalence (>10%, for roach in length class 25-30 cm) in roach from 4 sites in the Archipelago Sea, from one site influenced by cooling water dscharge from a nuclear power plant in Gulf of Bothnia, and in roach from one site close to a metal processing plant in the northern Gulf of Bothnia. The sites in the Archipelago Sea were not directly affected by industrial pollution. The disease was most prevalent in large (old) female roach, and it was characterized by degeneration of the ovaries ranging from weak tissue changes in one ovary to complete absence or destruction of both ovaries. Oocytes, in affected gonads, were frequently infected by a microsporidian parasite Pleistophora mirandellae. In males atretic testes were never observed and only small cysts, containing P mirandellae, were detected. In several affected roach, both male and female reproductive tissues were observed. The observed pathological changes in the ovaries of roach are suggested to be caused by P mirandellae.