The lake salmon or mpasa (''Opsaridium microlepis'') is an African species of freshwater fish, endemic to

Lake Malawi Lake Malawi, also known as Lake Nyasa in Tanzania and Lago Niassa in Mozambique, () is an African Great Lakes, African Great Lake and the southernmost lake in the East African Rift system, located between Malawi, Mozambique and Tanzania. It is ...

, in the family

Danionidae The danionins are a group of small, minnow-type fish belonging to the family Danionidae. Species of this group are in the genera clades ''Danio'' and '' Devario'' (which also includes ''Chela'', ''Laubuka'', ''Microdevario'', and ''Microrasbora ...

found in Malawi, Mozambique, and Tanzania. Its natural

habitat In ecology, habitat refers to the array of resources, biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species' habitat can be seen as the physical manifestation of its ...

s are

river A river is a natural stream of fresh water that flows on land or inside Subterranean river, caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of ...

s and freshwater

lake A lake is often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from ...

Description

It is a silvery fish which resembles trout of the family

Salmonidae Salmonidae (, ) is a family (biology), family of ray-finned fish, the only extant member of the suborder Salmonoidei, consisting of 11 extant genera and over 200 species collectively known as "salmonids" or "salmonoids". The family includes salmo ...

and lacks the pink or orange coloured fins of many of its congeners. They can grow to up to in weight and in total length The larger adults are plain coloured while the juveniles have vertical dark bars along the body which they lose as they grow.

Habitat and ecology

The lake salmon occurs in the pelagic zone of Lake Malawi, over sandy substrates. The juvenile fish stay close inshore near the mouths of the tributary rivers. The adults feed on small pelagic fishes, especially '' Engraulicypris sardella'', while the juveniles feed on plankton, insects and other small organic matter. During the rainy season the adult fish migrate up the tributary rivers from the lake to spawn, this mainly takes place at night in shallow, well-oxygenated, flowing waters over gravel substrates with no silt. there is an extended spawning period which starts with the onset of the rains and continues after the rains, from May to October. The young remain in the rivers until they have grown somewhat and are able to return to the lake.

Conservation

The lake salmon is threatened by overfishing and there are very high mortality rates in adult fish during the spawning season as the rivers are often totally blocked with weirs and with gill nets which prevent the fish from running upstream, especially during years of low rainfall. Other threats include deliberate poisoning and the deterioration of the spawning grounds due to siltation from soil erosion caused by deforestation and agriculture, which also causes habitat deterioration as water is abstracted from the breeding streams for irrigation and this makes it difficult for the juveniles to return to the lake from the spawning areas. It is caught using ring nets and by angling. The Bua River runs through the

Nkhotakota Wildlife Reserve Nkhotakota Wildlife Reserve (also known as Nkhotakota Game Reserve or Nkhotakota Wildlife Preserve), is the largest and oldest wildlife reserve in Malawi, near Nkhotakota. The park's hilly terrain features dambos and miombo woodlands as the domin ...

in central Malawi and this is the only river where the spawning grounds are protected because the surrounding woodlands are protected from clearing. The headwaters of another spawning river, the North Rukuru, are protected within the

Nyika National Park Nyika National Park is Malawi’s largest national park, with an area of 3200 km2 (1250 mile2). Location and road access The park covers practically the whole of the Nyika Plateau in northern Malawi, about 480 km north of Lilongwe and 60 km no ...

but there is increasing deforestation between the park and the spawning grounds. The Linthipe River is a major spawning river and it is unprotected being polluted with untreated sewage from the city of

Lilongwe Lilongwe (, ,) is the capital and largest city of Malawi. It has a population of 989,318 as of the 2018 Census, up from a population of 674,448 in 2008. In 2020, that figure was 1,122,000. The city is located in the central region of Malawi, i ...

. The condition of the spawning rivers in Tanzania and Mozambique is not known.

References

{{Taxonbar, from=Q2697181 Opsaridium Fish of Malawi Fish of Mozambique Freshwater fish of Tanzania Fish described in 1864 Taxa named by Albert Günther Taxonomy articles created by Polbot Fish of Lake Malawi