Movements of, and habitat utilisation by, threespot tilapia Oreochromis andersonii (Teleostei: Cichlidae) in the Upper Zambezi River, Namibia

Abstract

Movements of and habitat utilisation by radio-tagged threespot tilapia (body length 25–50cm) were studied in the Upper Zambezi River between 23 November 2000 and 8 May 2001. Although utilising a relatively large stretch of river (average 5.4km) during the study period, the fish mainly stayed within defined home ranges, with an average 95% utility distribution of 0.3km2. The individual variation was large, with the largest home range being 28 times larger than the smallest. A broad spectrum of habitats was used, with 39% of the 'fixes' lying in the main stream of the river, 26% in backwaters, 0.5% in the mouths of backwaters, 12% in channels, 16% in permanent swamps, and 7% on the floodplain. Mean width of the waterbody where the fish were positioned was 493m. Mean distance to the nearest shore was 158m, constituting 31% of the total river width. On average, 51% of the fixes were at vegetation, 39% away from vegetation, and 11% near vegetation. Mean water depth where the fish were recorded was 3.4m. Hence, adult threespot tilapia did not appear to be habitat specialists, but displayed flexible movement behaviour and habitat utilisation, with a large degree of individual variation.