An ichthyological borderland: The fishfauna of Nyungwe National Park and surroundings (Rwanda, East Africa)

Abstract

Nyungwe National Park (NP) is a mountainous region situated in the southwestern part of Rwanda on Congo-Nile watershed. In spite of the high biodiversity in primates, birds and plants, no fish were reported to occur in the park, probably because of the cold temperatures of the rivers. An expedition in 2022 examined the fish diversity within the Nyungwe NP and its buffer zones. Additional sampling was performed in the main river draining the park into Lake Kivu: the Kamiranzovu. Three hundred and twenty specimens belonging to 13 species were collected. Specimens were collected only in the western part of the park, draining towards the Congo basin. The diversity within the park proper was limited to two putative species within the complex of Amphilius cf. kivuensis, which were caught on either side of the Kivu-Rusizi watershed. In contrast, a higher fish diversity, including one clariid species and two species of Enteromius, was observed in the rivers at a lower altitude of the buffer zone. However, the highest species diversity was found near the mouth of Kamiranzovu River, including 11 species, of which 4 were non-native: the guppy Poecilia reticulata, Astatotilapia burtoni, the blue-spotted tilapia Oreochromis leucosticus and the Egyptian mouth-brooder Pseudocrenilabrus multicolor.