Fishes of the Kwilu River (Kasai basin, central Africa): A list of species collected in the vicinity of Kikwit, Bandundu Province, Democratic Republic of Congo

A list of fishes collected in the vicinity of Kikwit on the Kwilu River, a large left bank tributary of the Kasai River in the Democratic Republic of Congo is provided. One hundred and thirteen species distributed in 21 families are reported, and of these 29 species are recognized as representing new records for the region. Lack of up-to-date taxonomic and distributional knowledge of African fishes, a problem particularly acute in the central Congo basin, is clearly reflected in this high number of range extensions. While preliminary, this contribution serves as a useful starting point for efforts to understand the ichthyofaunal composition and biogeographic history of the Kasai system; one of the most poorly documented river systems in central Africa.


Introduction
The Kwilu is a large left bank tributary of the Kasai River, itself the main southern tributary of the Congo River that drains almost one third of the entire Congo basin. The headwaters of the Kwilu arise on the Kasai Shield in the Angolan highlands at an elevation of 1000-1800 meters above sea level (m.a.s.l.) and descend steeply towards the flat central Congo Basin (300-500 m. a.s.l.) in the Democratic Republic of Congo ( Figure 1). The Kwilu is about 965 km in length with a wet-season inundation area of 1550 km 2 (Hughes 1996). At its mouth the Kwilu joins the Kwango River just south of the provincial capital of Bandundu and together these two tributaries enter the main channel of the Kasai River some 50 km upstream of the Kasai-Fimi confluence. The Kwilu, like much of the Kasai system, is extremely poorly known ichthyologically ) and, as part of an ongoing survey of the fishes of the northwestern Kasai basin, collections of fishes were made along a 35 km reach of the Kwilu River in the vicinity of Kikwit, a river port some 250 km upstream of Bandundu.
Here we provide a preliminary list of fishes collected in the Kwilu main channel in the region of Kikwit. Although undoubtedly incomplete, given the paucity of information on the fishes of this system we believe that this list serves as a useful starting point for efforts to understand the ichthyofaunal composition and biogeographic history of the Kasai system; one of the most poorly documented river systems in central Africa. Future collections in the region are planned, with an emphasis on collecting the numerous, small affluent streams feeding into the main channel of the Kwilu. Efforts to collect upstream where numerous rapids and cataracts accompany the narrowing of the channel as it approaches the Angolan border, is challenging but will undoubtedly render additional species and serve to complete this inventory.
Check List | Volume 7 | Issue 5 | 2011 Abstract: A list of fishes collected in the vicinity of Kikwit on the Kwilu River, a large left bank tributary of the Kasai River in the Democratic Republic of Congo is provided. One hundred and thirteen species distributed in 21 families are reported, and of these 29 species are recognized as representing new records for the region. Lack of up-to-date taxonomic and distributional knowledge of African fishes, a problem particularly acute in the central Congo basin, is clearly reflected in this high number of range extensions. While preliminary, this contribution serves as a useful starting point for efforts to understand the ichthyofaunal composition and biogeographic history of the Kasai system; one of the most poorly documented river systems in central Africa.  Figures 2E and 3D) is situated upstream of a series of rapids formed where the river width rapidly narrows. At Carrefour, the river widens to a width of about 20 m, and is reportedly extremely deep (no depth measurement was possible at this site). The shoreline is fringed with high gallery forest, with some small-scale agricultural plots and localized disturbance. Close to this site a series of large ponds (etangs) have been dug and villagers stock these with fishes collected in the river, as well as the widely introduced cichlid, Oreochromis niloticus (Linneaus, 1758). Periodically the ponds are drained and the fishes harvested ( Figure 3F). Site 6 (Ibanzi, Figure 2F) is the southernmost site sampled and separated from Site 5 by a series of large rapids. The entire shoreline is heavily forested with little disturbance. The riverbed is extremely rocky, with large blocks of rock strewn along the shoreline and small, interspersed sandy beaches.

Fish sampling
Only locally acceptable fishing practices were employed for this survey, and these constitute three main techniques: cast nets deployed from wooden pirogues (canoes) in deep water, seine nets of varying sizes, commonly used by local fishing collectives, over sandy substrates ( Figure 3B) and the third method employed was "Sambwisa", the local name for a particular use of a fine-mesh seine (made from mosquito netting). The latter technique involves encircling a large area of dense vegetation within the Sambwisa and then physically removing every blade of vegetation until only fish remain in the fine mesh net ( Figure 3C). This technique is highly effective when carried out by experienced teams of fishermen, but is unfortunately extremely destructive to the vegetation.
Taxonomic nomenclature used herein follows Brooks et al. (2011), which is based primarily on Eschmeyer (2010) but with a few modifications. All fishes were collected and exported with permission of the Congolese Ministère de l' Agriculture, Secrétariat General à l' Agriculture, Pêche et Elevage, Direction des Pêches (Permit# 07/DP/SG/ AGRI/2010 and Permit# 03/DP/SG/AGRI/2011, both on file at AMNH).

Results and Discussion
A total of 1074 individuals belonging to 113 species, distributed in 21 families and eight orders are represented in Table 2, with their distribution among sites indicated in columns 1-6. In column 7 distribution data culled from the recently published IUCN assessment of the status and distribution of central African fishes (Brooks et al. 2011), is used to indicate which of the Kwilu species are known to occur in the broad region of the Kasai drainage. The data for the IUCN assessment is a compilation of point data drawn from Stiassny et al. (2007) and from legacy collections housed in the Africa Museum, Tervuren (MRAC) and the AMNH, that has been reviewed by taxonomic experts prior to publication (Darwell and Smith 2011). While these comparative data are minimal for the Kwilu River itself, Brooks et al. (2011) do provide data on fishes from the Kasai main channel and certain Kasai tributaries, thereby providing the best available comparison for the Kwilu River list provided herein. Based on these data we tentatively recognize 29 species represented in our Kwilu collections that have either not previously been recorded from the Kasai basin or are known only from isolated regions of the Kasai distant from the Kwilu. Most of these species (Table 2\) represent significant range extensions within the Congo basin, and a selection of such are illustrated in Figures 4 and 5. A single exotic species, Oreochromis niloticus, was found during the survey at site 5 (Carrefour). The specimen is presumably an escapee from one of the fish ponds situated inshore near the village of Carrefour ( Figure 3F). Lowenstein et al. (2011) highlight the problems associated with compiling species inventories in the absence of up-to-date taxonomic and distributional knowledge of African fishes, a problem particularly acute in the central Congo basin. We acknowledge that insufficient taxonomic research has been conducted on much of the region's ichthyofauna and that some identifications to species presented here should be considered tentative, but nonetheless represent the best data available for the region.   Table 2. List of species collected at sites 1-6 along the main channel of the Kwilu River near Kikwit. In column 7 distribution data culled from a recently published IUCN assessment of the status and distribution of central African fishes (Brooks et al. 2011), is used to indicate which Kwilu species are known to occur in the broad region of the Kasai drainage.
Mbimbi and Stiassny | Fishes of the Kwilu River, Democratic Republic of Congo