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Snorkelling surveys using a point abundance method revealed high levels of microhabitat differentiation among 14 fish species from a high-visibility site in the middle reaches of the Gambia River. Habitat segregation was most strongly related to the position in the water column, flow velocity, substratum composition and presence of submerged wood. [ABSTRACT FROM AUTHOR]

The osteology of a population of the characiform fishAlestes stuhlmannii, from the Rufiji River basin of Tanzania, is described, and meristic and morphometric data from over 100 specimens, ranging from 15·5 to 218 mm standard length are given. Two allometric changes occur during growth of this fish: both the number of gill rakers and the interorbital width relative to the head length increase with size. There are also changes in tooth form associated with growth inA. stuhlmannii, with the unicuspid teeth of juveniles becoming almost molariform in adults. This change in dentition with age, and therefore size, may have implications for recognizing taxa, some of which(the fossil generaSindacharaxandBunocharax, and the living dwarf petersiines) have been distinguished by jaw or dental characters. [ABSTRACT FROM AUTHOR]