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Despite the increasing recognition that in-stream movement probably represents an important aspect of the ecology of many stream fish populations, there is still limited and often conflicting information on the movement behaviour of a wide range of fish, especially species that are threatened and/or with no economic interest. In this study, movement behaviour of the endangered bullhead (Cottus gobio), a small, bottom-dwelling European freshwater fish, was assessed by mark-recapture in a Flemish (northern part of Belgium) lowland river between September 2002 and May 2003. The majority (61-72%) of tagged bullheads recaptured during the different sampling occasions were found at or near (< 10 m) their initial tagging site. The other re-sighted specimens however had covered distances between 20 and 270 m. There were no significant indications of seasonal differences in bullhead movement behaviour. In general, our results strongly suggest that bullhead populations not only consist of stationary individuals but also of relatively mobile fish. Consequently, to effectively conserve this endangered species, fisheries managers should (i) consider sufficiently large areas of habitat as critical to bullhead populations, and (ii) minimise the impact of physical barriers on bullhead movement. [ABSTRACT FROM AUTHOR]