Three species of the Eurasian family Cobitidae are distributed in Slovakia. In the present paper, we describe the coenological affinity of Cobitis elongatoides, Sabanejewia balcanica and Misgurnus fossilis in two distinct zoogeographical regions, Slovak Tisza and Danube basins and discuss possible differences of their biotop affinity and habitat preferences. The occurrence of S. balcanica is restricted to primary biotopes with harder substratum particles. Typical species assemblages for the rheophilic C. elongatoides are eurytopic and limnophilous species. C. elongatoides is mostly distributed in primary biotopes, such as rivers and channels. It also occurs in secondary biotopes (drainage canal or pit). M. fossilis is distributed mostly in the secondary biotopes, but it is also found in the primary biotopes. Both species prefer fine substratum, but spatial distribution of the two species is different. C. elongatoides prefers harder substratum of sandy particles mixed with mud or detritus and living vegetation, whereas M. fossilis prefers muddy substratum mixed with detritus and dead vegetation.
During a survey on the biology of Cobitis cf. turcica living in Pınarbaşı 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.