Hydrocynus vittatus

Hydrocynus vittatus
Small H. vittatus specimen from the upper Zambezi
Conservation status
Least Concern  (IUCN 3.1)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Characiformes
Family:	Alestidae
Genus:	Hydrocynus
Species:	H. vittatus
Binomial name
Hydrocynus vittatus (Castelnau, 1861)

Hydrocynus vittatus, the African tigerfish, tiervis or ndweshi is a predatory freshwater fish distributed throughout much of Africa. It has been observed leaping out of the water and catching swallows (Hirundo rustica) in flight.

Appearance

The African tigerfish is overall silvery in colour, with thin black stripes running horizontally. It has an elongated body and a red, forked caudal fin with a black edge. Its head is large, as well as its teeth, of which there are eight per jaw. Males are larger and more full-bodied than females. It grows to a length of 105 centimetres (41 in) SL.

Distribution

This species' distribution covers the Niger/Bénoué, Ouémé River, Senegal River, Nile, Omo River, Congo River, Lufira, Lualaba River, Luapula, Zambezi, Limpopo River, Rovuma, Shire River and Wami River; as well as Lakes - Lake Bangweulu, Moéro, Tanganyika, Upemba, Rukwa and Malagarazi. It is also found in the Okavango Basin and lower reaches of coastal systems south to the Pongola River and in man-made Lake Kariba and Schroda Dam.

Habitat and ecology

A demersal, migratory freshwater species, Hydrocynus vittatus prefers warm, well-oxygenated water, mainly in larger rivers and lakes. The smaller individuals form roving schools of like-sized fish; aptly described as fierce and voracious but very large specimens may be solitary. It preys on most abundant fish species available, but species of the genera Brycinus, Micralestes, Barbus, and Limnothrissa are favoured prey. Breeding occurs on a few days each year, when the initial rains have swollen the rivers and streams, normally in December and January when a spawning migration is undertaken upstream into rivers and smaller streams. The females spawn a great number of eggs in very shallow water, among the stems submerged and partly submerged vegetation where the fry stay until the receding of the flood water makes them return to the main channels.

A highly unusual feeding behavior has been seen in the Schroda Dam population of Hydrocynus vittatus. The fish jump out of the water and catch barn swallows (Hirundo rustica) on the wing as they fly near the surface of the lake feeding on insects. The researchers observed an average success rate of 25% for predation attempts, with as many as twenty birds caught per day over a relatively small lake (4.1 x 10⁶ m³). This is the only documented instance of a freshwater fish exhibiting this behavior.

Population and conservation status

This species is common and widespread over most of its range. In the most studied population, that of Lake Kariba on the Middle Zambezi River, the population fluctuated markedly, apparently in direct relation to the abundance of the introduced clupeid Limnothrissa miodon which forms a major part of its diet. There is a commercial fishery in Lake Rukwa, where it forms about 3.9% of the yield.

Hydrocynus vittatus have declined in some river systems in southern Africa as a result of pollution, water abstraction and obstructions by dams and weirs that prevent migration. It is locally threatened by unregulated gillnet fisheries. In east Africa, threats to populations include overfishing, reductions in water quality due to agricultural activities and deforestation, and pesticide pollution.

External links

• Phillipson, David W. 1985. Mosi-oa-Tunya A Handbook to the Victoria Falls Region Long man Zimbabwe ISBN 0-0546-8657