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Fifteen adult nembwe Serranochromis robustus (Günther, 1864) were tagged with radio transmitters in the Zambezi River, Namibia, from 4–15 November 2000 to record behaviour and outline the implications for fisheries management. The fish were tracked on average every 3.7 days until 18 May 2001. They stayed within relatively small home ranges, with a 95% probability of localization within an average area of 184 563m2. The fish utilized a mean river stretch of 1330 m (range = 24– 3787). Nembwe were recorded in a variety of habitats, and the individual variation in movements and habitat use was substantial. All the fish were recorded in the mainstream of the river, but 62% of the fish were recorded in one or more additional main habitat types. During rising and high water, 67% and 71% of the fish, respectively, were recorded in adjacent temporary flooded areas during some or all tracking surveys, but did not undertake long-distance migrations onto the floodplains. It is concluded that although staying within relatively small home ranges, nembwe appears as a species with a variable and flexible habitat utilization.Keywords: fish, radio-tagging, telemetry, home range, behaviour, fisheries management

In the Upper Zambezi and Okavango ecoregions, Brycinus lateralis, Hepsetus cuvieri, Schilbe intermedius and Serranochromis macrocephalus are important in subsistence fisheries, while S. intermedius and S. macrocephalus are often caught in commercial catches. Despite their importance, there is little information on their age and growth and age validation. Growth zone deposition rate in otoliths of B. lateralis, H. cuvieri, S. intermedius and S. macrocephalus was validated as annual using edge analysis in this study. Annual deposition of growth zones was corroborated by a fluorochrome marking experiment. Both methods demonstrated that one growth zone was deposited annually. Edge analysis demonstrated that the highest proportion of opaque zones was detected between August and December, most likely as a result of slow growth during lower temperature water during the preceding winter. With growth zone deposition validated as annual, future research should focus on determining the growth, maturity and mortality rates of these species, parameters which are important for their management.Keywords: Brycinus lateralis, Hepsetus cuvieri, Schilbe intermedius, Serranochromis macrocephalus