The true diversity of our fish
The true diversity of our fish
One of the main attractions of sport fishing in the Zambezi River is the variety of species that can be caught. What many anglers don’t realise is that the number of species they catch is a small proportion of the species that actually occur in the river and surrounding lagoons and floodplains.
The fish fauna of the section of river targeted in the annual International Zambezi Classic angling tournament held in Caprivi in August is supposedly well-known. About 80 fish species are currently recognised, almost all which are well-illustrated in Paul Skelton’s ‘Field Guide to the Freshwater Fishes of Southern Africa.’ But surprises still turn up for ichthyologists looking closely. The Caprivi fish list will be expanded, and not only by the addition of new, small species that were previously overlooked.
The most surprising discovery is of a large bream that does not fit any of the known described species. This species, to which we have given the common name ‘dusky bream,’ is one of the biggest bream species in the river and is caught by anglers, so competitors should watch out for this ‘new’ species.
The dusky bream is similar to the well-known pink bream but is much darker in colour and is deeper-bodied with a much more steeply-sloping forehead. Scientists from the South African Institute for Aquatic Biodiversity (SAIAB) in Grahamstown, working closely with Namibia’s fisheries ministry, have now found this fish in the Kwando and Kavango rivers as well as the Zambezi.
Tissue samples have been taken from specimens recently collected, as well as from other similar breams, to carry out a genetic study and see just how different these species are. So far, only large specimens have been found, so SAIAB scientists are now looking at juvenile Sargochromis specimens collected over the years to see if they can separate and identify the different species at small sizes.
New discoveries continue to be made in the smaller species also. The tiny, three centimetre long catfish listed in Skelton’s book as Leptoglanis sp. and given the name ‘Chobe sand catlet’ has now been formally named as Zaireichthys pallidus, while another, more boldly marked species found in the rapids around Impalila Island has been named Zaireichthys conspicuus. In both of these species, the scientific names given to them describe them well. Zaireichthys pallidus is a small, very pale species, while the name Zaireichthys conspicuus refers to the bold markings on this more robust species.
In an earlier Zambezi Traveller, an article was published on another new bream species found in Lake Liambezi. Variation in the ‘Zambezi happy’ puzzled one of Africa’s foremost fish taxonomists, Humphry Greenwood, in the 1970s. This led him to lump all the Zambezi and Angolan forms together under the scientific name Pharyngochromis acuticeps until such time as the problem could be resolved. A large number of specimens have now been collected to try and solve this problem but the situation remains unresolved. It might, however, be possible to get an answer by DNA analysis of muscle tissue.
More than 20 species, several of which are new to science, are found further north in the smaller tributaries of the Upper Zambezi in northern Zambia. Many are shared with southern Congo tributaries. Resolving all these questions will occupy SAIAB’s scientists for years to come.
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Zambezi Traveller (Issue 08, March 2012)