Possible Effects of Black-Spot Disease on Northern Pike

Abstract

Twenty-two percent of 623 Niagara River northern pike Esox lucius we examined had black-spot disease. An attempt to identify the causative digenic trematode was unsuccessful. Infected fish were smaller than uninfected fish at ages 1, 2, 3, and 4 years, and the size differential increased with age. Incidence of infection decreased as fish age (and length) increased so that no fish older than 4+ years (or longer than 600 mm total length) had black-spot disease. The proportion of diseased fish recaptured after several months at large was less than that for uninfected fish, but sample size was small. These data suggest that black-spot infection is related to retarded growth and increased mortality, but cause and effect are unclear.