Fish pass effectiveness for bullhead (Cottus gobio), perch (Perca fluviatilis) and roach (Rutilus rutilus) in a regulated lowland river Un resumen en españ ol se incluye detrás del texto principal de este artículo.Abstract -The effectiveness of a pool-and-weir fish pass in the regulated river Laarse Beek (Belgium) was assessed for bullhead (Cottus gobio), perch (Perca fluviatilis) and roach (Rutilus rutilus) from August 2002 to April 2003. Fish were caught by electrofishing downstream, within and upstream of the fish pass. They were marked with visible implant elastomer tags and released downstream of the fish pass. Our results suggest that the fish pass is ineffective for the bullhead because none of the 1270 tagged bullheads were recaptured in the upstream study area. Passage failure most likely resulted from excessive water velocities in the fish pass. On the contrary, 8% of the tagged perch and 29% of the tagged roach were recaptured in the upstream study area. Several management strategies are proposed to allow free upstream passage of the endangered bullhead at the fish pass under study.

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 markrecapture 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.