Abstract
Amphilius uranoscopus is a catfish species, restricted to rivers and streams in east, southern and central Africa. It is likely to be displaced due to both competition and predation by exotic trout and other introduced fish. In high altitude mountain streams it can be the only species occurring, which means that this habitat may act as a refuge for this species. Ecosystems like this are threatened by habitat alteration and are therefore in need of protection. The abiotic environment, population structure, behavior and feeding biology of Amphilius uranoscopus were studied in a small, high-altitude perennial tributary of the Limpopo River in the Soutpansberg mountain range, Limpopo Province, South Africa, during 2005–2006. Here A. uranoscopus showed nocturnal behavior. It used dark hollow crevices in rapids as shelters during the daytime. The rapids are characterized by a high flow rate, high dissolved oxygen content and coarse riverbed substrate consisting mainly of boulders without fallen leaves. In contrast to the adults, juveniles found shelter among the fallen leaves in pools. At night, A. uranoscopus moved out of the rapids into the open water of the pools. The main food of A. uranoscopus consisted of macroinvertebrates, mainly Trichoptera larvae. Amounts of algae and detritus in its diet were negligible. A. uranoscopus foraged mainly in rapids and on rock surfaces, spending less time foraging between the fallen leaves at the bottom of pools, in open water, at the surfaces of bottom and bank and near the water surface. At the water surface, it also fed opportunistically on terrestrial insects that dropped into the stream, like flying termites. A. uranoscopus was the top predator of the stream system and reached a high density (0.71 fish m−2). There was no competition from other fish species at the study site as they were lacking. A. uranoscopus showed a striking ability to climb and cling on to vertical substrates to conquer waterfalls and very shallow streams that sometimes become dry, using its fins, adhesive body and protruding mouth teeth.
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Acknowledgements
We would like to thank the Stichting Nijmeegs Universiteitsfonds for a grant; M. Orbons for her assistance with the lab work; J. Eygensteyn for the analysis of the stable isotopes; the fieldwork assistants J. Sloothaak, K. Bäuerle, J. Jones, A. Tasire and C. Keller for their help during the stream surveys; J. Sloothaak, I. Laas and S. Gaigher for their help building the artificial stream; B. Barth and C, Keller for their company during night observations; M. Garfinkel for editing; F. Charko for editing and for her help gathering specimens for the stable isotope analysis; R. van Montfoort for ICT support; and P. Fouche and S. Foord of the University of Venda for providing us with a flow meter plus box net and for their assistance with the identification of macroinvertebrates. This is CWE publication no. 504.
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van Oosterhout, M.P., van der Velde, G. & Gaigher, I.G. High altitude mountain streams as a possible refuge habitat for the catfish Amphilius uranoscopus . Environ Biol Fish 84, 109–120 (2009). https://doi.org/10.1007/s10641-008-9394-y
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DOI: https://doi.org/10.1007/s10641-008-9394-y