During a survey on the biology of Cobitis cf. turcica living in Pinarbasi Springs (Haymana district, Turkey), symptoms of black spot disease were frequently observed on the specimens. Of the 1295 loach collected, 240 (19 %) specimens were found to be infected with metacercaria of Posthodiplostomum cuticola, a common digenean parasite causing black spot disease in freshwater fish in Eurasia. During spring and autumn, the infection rate was significantly higher than during winter and summer, most probably due to the increasing density of migration of birds in this area. No statistically significant difference was found in condition, weight and length between infected and non-infected specimens; indicating low physiological effects of the encysted metacercaria on the host specimens. However, the prevalence of black spot had a tendency to decrease with age, remarking a higher mortality rate of infected specimens. This increased mortality rate seems to be the most important impact of an infection with metacercaria for a Cobitis population.