The focus of this post was the headwaters of the Kasai River, also known as the Cassai River, which is located within the Congo Peneplain in Lunda Sul Province, Angola. Nutrient poor landscapes have formed a mosaic of miombo woodland, geoxylic suffrutex grasslands and wetlands. The sandy well drained soils and flat topography have formed extensive wetland complexes with associated peat deposits.
The wetland types are classified as channeled valley bottom wetland hydrogeomorphic units but are also associated with oxbow-lake's, permanent and seasonal floodplains. The deep sandy soils, peat and floating reedbeds have produced extremely clear water that barely fluctuates in elevation between the seasons. This continual state of inundation with limited fluctuation and clear waters has produced densely vegetated river beds and floodplains.
Hydraulic units included runs, with both sand, gravel and vegetated substrates. Where vegetation such as Syzygium confined the flow of water, pools and riffles were formed. The confined flow exposed bedrock structures where stands of submerged Eleocharis species would be present. Within the ox-bow lake systems and slower flowing waters dense stands of colorful Limnophila sp were found, whilst tightly packed vegetated slow flowing runs contained stands of Nymphea, Nymphoides, Ottelia and numerous obligate wetland taxa. The study area was noted to have stands of swamp forest which served to further diversify the aquatic habitats.
Water chemistry showed low pH between 5.1 and 5.6 , low conductivity, turbidity, dissolved salts, nutrients and metals. This was an expected result given to the weathered nature of the Congo Peneplain as well as the natural state of the watershed. Although iron and copper was indicated to be present at low concentrations, its expected that this may be a laboratory error.
Paul Skelton provided a revision of the fishes of Angola in a chapter of the Biodiversity of Angola Book (https://doi.org/10.1007/978-3-030-03083-4_11) where the state of ichthyological knowledge in the region was be regarded as poor. Poll 's (1967) work was completed in drainages of the Dundo River basin around the town of Saurimo, in proximity and possibly including studies from similar habitat types as observed in this study.
According to Skelton (2019) the estimated species abundance in the southern Congo tributaries was 162 species where the fish fauna consists of a mixture of the Congo and Zambezian ichthyological provinces. In the Saurimo region, Poll (1967) recorded 108 species in the Cassai, 28 in the Luangwe and 37 in the Kwilu Rivers (Skelton, 2019).
Over two surveys in October and March, approximately 27 fish species were observed. The fish community consisted of the typical fauna, where Congo species such as Bryconaethiops boulengeri and Distichodus sp. as well as typical Zambezi fauna such as Hemichromis elongatus, Microctenopoma intermedium and Parauchenoglanis ngamensis were found. It is noted that all species depicted here are tentatively identified, should these require correcting please get in touch with us.
The dominant family present were represented within the family Cyprinidae, where Enteromius was the most frequently observed and abundant genus in the sites. Five species of Enteromius were caught and included the colorful Enteromius chiumbeensis. Schools of large Enteromius sp. and Distichodus were also seen to occupy deeper habitats including runs and pools. The larger Enteromius were great fun to catch on fly-rod but were otherwise very difficult to catch (using electrofishing and cast nets).
Siluriform catfishes were well represented during the survey. Species known to be sensitive to flow and bed modification such as Phractura macrura or scaphyrhynchura and Amphilius lentiginosus. These were observed where flows concentrated and in-between the dense matts of aquatic vegetation.
Within the vegetative cover, on the wetland floodplains and between submerged woody debris, catfish species such as Schilbe marmoratus, Synodontis macropunctatus and Parauchenoglanis ngamensis were found. Between floodplain vegetation species such as Clarias cf. strapperssi were caught using earthworms and angling, Marcuesnius and Ctenompoma multispine. Two apparent species of Spiny Eel were also caught and included Mastacembelus frenatus and Mastacembelus congicus, these species were found in varying habitats throughout the study area.
An interesting finding from the survey was the limited presence of Alestidae which were noted to only include what appears to be Micralestes humilis. These fishes were abundant in the pool and flowing habitats as seen in the video below. It is noted that Micralestes acutidens and Hydrocynus vittatus are also expected to be present although these were not seen during the surveys.
Within the wetland habitat as well as the very densely vegetated margins of the main river the Lampeye, Micropanchax luluae and Nannocharax lineostriatus. Unfortunately only a single Micropanchax luluae female was observed.
The Peso River reach surveyed was found to contain a population of species which resembled both Tilapia ruweti and Tilapia sparrmanii. A video of these species is shown below. As seen in the video a clear red/purple breast is present on the Tilapia which is not commonly observed in the species in the Zambezi system. Similarly, the T. ruweti does not conform to the standard description of the species and therefore likely represents undescribed species.
Within the peat wetland systems, small pockets and pools of open water would be present. Sampling of this habitat revealed the presence of Dundocharax bidentatus as well as what looks to be Microctenopoma stevenorrisi, the newly described species (Skelton, 2021). The photograph presented below is the first image of Dundocharax bidentatus in life.
This page will hopefully be continually updated as more information becomes available. Summaries of the habitats can also be found on the youtube links below.
There is also still alot of work that needs to be done on these fishes!
REFERENCES
Poll M. 1967. Contribution à la Faune Ichthyologique de l’Angola. Publicaçōes Culturais 75 75. Companhia dos Diamentes de Angola (DIAMANG), Lisbon, 381 pp.
Skelton PH. 2019. The Freshwater Fishes of Angola. In: Huntley, B., Russo, V., Lages, F., Ferrand, N. (eds) Biodiversity of Angola. Springer, Cham. https://doi.org/10.1007/978-3-030-03083-4_11.
Skelton PH, Stauffer JR, Chakona A, Wisor JM. 2021. Two new species of African bubble-nesting Microctenopoma (Teleostei: Anabantidae) from Angola. Ichthyological Exploration of Freshwaters IEF-1134: 1-16.