Where they live
Fish don’t just swim anywhere in the rivers of the Congo River Basin. In fact, most of them are picky and will only live in particular areas. These include:
- Channels, creeks and oxbows, with shaded calm pools, little current, sand or mud bottoms rich in vegetable debris;
- Floating meadows, along banks; and
- Inundation zones.3
Fish are particularly fond of the shallow waters along riverbanks and islands, where the slower current and clearer water favour the availability of food.
How fish use the river habitat
Some species have evolved to take advantage of nature’s gifts. For instance, young catfish, characids and mormyrids seek refuge from predators by keeping close to plants such as the water hyacinth, which grows on the riverbanks.
Plants and insects that are found in such habitats provide food for the young and adults of many fish species. For some species of fish, fallen trees and submerged logs from riparian forests are an important habitat.
Other species prefer rocky bottoms, which provide a stable substrate, while others again have adapted to low oxygen and varying water levels in swamps.
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Underwater lifestyles in the Congo River Basin
Fish species are not necessarily restricted to one kind of habitat. In fact, many change from one habitat to another during different stages of their lifecycle, for example spawning and feeding. Young may spend their juvenile stage in a flooded zone and migrate to the main part of the river when mature.
The onset of the rainy season signals the beginning of breeding for river fishes. This happens twice a year, the most important for Congolese fishes being during the major rainy season (September-October in general), with a second, lesser breeding period during the rainy season from April to June.
As water levels rise, there is an explosion of microorganisms and aquatic vegetation that leads to an increase in small invertebrates. This coincides with the juvenile stage of fish, when the needs for feeding and growing are the greatest.
The impact of fish capture
While fisher folk usually use gill nets, seine nets, cast nets, hand lines and fish baskets, some have broadened their arsenal to include defoliation of banks (using poisons or herbicides), explosives, poisons and illegally sized nets (mesh sizes of less than 3 cm).
These practices, along with overfishing, the introduction of alien fish species and probably deforestation have led to the decline of several species, including
Parachanna spp., Distichodontus spp., Gnathonemus spp. and
Protopterus spp. There has also been a decrease in diversity among the Bagridae, Characidae, Cyprinidae and Distichontidae families.
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1 Shumway C,
et al. 2003.
Biodiversity Survey: Systematics, Ecology, and Conservation Along the Congo River.
Congo River Environment and Development Project (CREDP).
2 Shumway C,
et al. 2003.
Biodiversity Survey: Systematics, Ecology, and Conservation Along the Congo River.
Congo River Environment and Development Project (CREDP).
3 Mathes, 1962 in Shumway C,
et al. 2003.
Biodiversity Survey: Systematics, Ecology, and Conservation Along the Congo River.
Congo River Environment and Development Project (CREDP).
4 Mathes, 1962 in Shumway C,
et al. 2003.
Biodiversity Survey: Systematics, Ecology, and Conservation Along the Congo River.
Congo River Environment and Development Project (CREDP).
5 Mathes, 1962 in Shumway C,
et al. 2003.
Biodiversity Survey: Systematics, Ecology, and Conservation Along the Congo River.
Congo River Environment and Development Project (CREDP).
