Oreochromis esculentus

Taxonomy

Assessment Information

Geographic Range

Population

Habitat and Ecology

Threats

Conservation Actions

Taxonomy [top]

Kingdom	Phylum	Class	Order	Family
ANIMALIA	CHORDATA	ACTINOPTERYGII	PERCIFORMES	CICHLIDAE

Scientific Name:

Oreochromis esculentus

Species Authority:

(Graham, 1928)

Common Name/s:

English

–

Singidia Tilapia

Assessment Information [top]

Red List Category & Criteria:

Critically Endangered A2bcde ver 3.1

Year Assessed:

2006

Assessor/s

Twongo, T.K., Bayona, J.D.R. & Hanssens, M.

Evaluator/s:

Snoeks, J. (Freshwater Fish Red List Authority) & Darwall, W. (Freshwater Biodiversity Assessment Programme)

Justification:
This species has almost been eliminated from its previous range in lakes Victoria and Kyoga through predation, competitive exclusion and ecological displacement by introduced fishes (Twongo 1995, Nagayi Kalule 1999). The main population (in Lake Victoria) has declined by >80% over the past 20 years (FIRRI fishery records, Mugeriya, pers. comm.). The remaining population is limited to sub-populations in a few satellite lakes, which are themselves undergoing continued environmental degradation and heavy fishing pressure. This species is assessed as Critically Endangered.

History:

1996

–

Vulnerable (Baillie and Groombridge 1996)

Geographic Range [top]

Range Description:	Present within the Lake Victoria drainage and Lake Kanyaboli. It has been introduced into several dams and waters, including the Pangani system (Lake Jipe). It is still present in some of the satellite lakes of Lakes Victoria and Kyoga. It is, however, virtually extinct from the main Lakes Victoria and Kyoga.
Countries:	Native: Kenya; Tanzania, United Republic of; Uganda

Population [top]

Population:	Declining.
Population Trend:	Decreasing

Habitat and Ecology [top]

Habitat and Ecology:	This species was originally (before competitive exclusion by the introduced species) confined to water less than 20 m deep and was most abundant in sheltered gulfs and bays where the bottom is composed of soft algaceous mud (Witte and de Winter 1995). It is a plankton feeder, using the mucus-trap mechanism combined with the combing action of the pharyngeal teeth. It is non selective all organisms of a size capable of being retained are passed into the stomach (Trewavas 1983). Breeding fish are found throughout the year and distinct spawning areas can be identified in the lake. Females brooding eggs often move off to the shelter of macrophyte beds or swampy areas. The young become independent at a length of about 15 mm when they are often found in channels in papyrus swamps (Trewavas 1983). Max Size: 248 mm SL (Trewavas 1983).
Systems:	Freshwater

Habitat and Ecology:

This species was originally (before competitive exclusion by the introduced species) confined to water less than 20 m deep and was most abundant in sheltered gulfs and bays where the bottom is composed of soft algaceous mud (Witte and de Winter 1995). It is a plankton feeder, using the mucus-trap mechanism combined with the combing action of the pharyngeal teeth. It is non selective all organisms of a size capable of being retained are passed into the stomach (Trewavas 1983). Breeding fish are found throughout the year and distinct spawning areas can be identified in the lake. Females brooding eggs often move off to the shelter of macrophyte beds or swampy areas. The young become independent at a length of about 15 mm when they are often found in channels in papyrus swamps (Trewavas 1983). Max Size: 248 mm SL (Trewavas 1983).

Systems:

Freshwater

Threats [top]

Major Threat(s):	Displacement by introduced fishes notably Nile perch and Nile tilapia. Heavy fishing pressure: over-fishing was reported by Horril (2000) as the cause for population decline, reduction in harvestable size and size at first maturity. Marked reduction of diatoms from the phytoplankton of Lakes Victoria and Kyoga at the expense of 'unpalatable' Cyanobacteria. Massive Typha species infestation of the spawning and nursery grounds. Increased siltation due to agricultural and cattle grazing practice in the area. Clearance of water-laden woodlands for agriculture (land encroachment), especially in the northwest, and for fuel wood. Pollution from domestic and agricultural effluents.

Major Threat(s):

Displacement by introduced fishes notably Nile perch and Nile tilapia. Heavy fishing pressure: over-fishing was reported by Horril (2000) as the cause for population decline, reduction in harvestable size and size at first maturity. Marked reduction of diatoms from the phytoplankton of Lakes Victoria and Kyoga at the expense of 'unpalatable' Cyanobacteria. Massive Typha species infestation of the spawning and nursery grounds. Increased siltation due to agricultural and cattle grazing practice in the area. Clearance of water-laden woodlands for agriculture (land encroachment), especially in the northwest, and for fuel wood. Pollution from domestic and agricultural effluents.

Conservation Actions [top]

Conservation Actions:	No information available.

Conservation Actions:

No information available.

Citation:	Twongo, T.K., Bayona, J.D.R. & Hanssens, M. 2006. Oreochromis esculentus. In: IUCN 2008. 2008 IUCN Red List of Threatened Species. <www.iucnredlist.org>. Downloaded on 07 January 2009.
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