Overview

Comprehensive Description

Biology

Occurs in both river and swamp habitats and is adapted to fairly fast-flowing rivers (Ref. 2, 6465). Hardy, tolerating fresh and brackish water (up to 20‰, Ref. 3), preferring slow-flowing or standing water; adults occupy deep open waters, juveniles remain inshore among vegetation (Ref. 7248, 52193). Prefers fairly deep, quiet water with some weed cover; hippo pools are a favoured retreat (Ref. 12524, 13337). Forms schools (Ref. 2, 12524, 13337). Mainly diurnal; a detritivore which feeds on fine particulate matter (Ref. 2), including algae (Ref. 246, 12524, 13337, 53992), diatoms, detritus (Ref. 7248, 52193, 53992) and zooplankton (Ref. 7248, 52193). Larger individuals also take insects and other invertebrates (Ref. 53992). Feeding regime is variable, the diet changes according to food availability (Ref. 6465). Female mouthbrooder (Ref. 87, 246, 6465, 12524, 13337). Fine angling and table species (Ref. 6465, 12524, 13337).
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Distribution

Range Description

This species occurs in the upper Zambezi, as well as the Kafue, Okavango and Cunene Rivers. Occasionally also recorded from the Middle Zambezi (Skelton 2001).

In East Africa, the species was introduced in Kenya in 1980 from Botswana (Motiti Pan, Okavango drainage) by I. Parker for aquaculture purposes. It was introduced to a dam near Nairobi and it is possible that some specimens found their way into the Nairobi River system.
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Africa: Ngami basin, Okavango River; Cunene River and Mossamedes, Angola; upper Zambezi, Kafue River; middle Zambezi, Lake Kariba and Cabora Bassa since construction of dams. Several countries report adverse ecological impact after introduction.
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Southern Africa.
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Physical Description

Morphology

Dorsal spines (total): 15 - 18; Dorsal soft rays (total): 11 - 15; Analspines: 3; Analsoft rays: 9 - 13; Vertebrae: 30 - 32
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Size

Maximum size: 500 mm SL
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Max. size

61.0 cm TL (male/unsexed; (Ref. 40637)); max. published weight: 4,710 g (Ref. 40637); max. reported age: 13 years (Ref. 13400)
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Diagnostic Description

Diagnosis: male genital papilla bluntly conical with a narrow flange slightly notched in the middle; jaws enlarged in breeding males, which in this species are normally not less than 30cm TL; scales in lateral line series 31-35, usually 32-33; scales of cheek in 3 full rows; vertebrae 30-32; total number of dorsal rays 28-31. Pectoral fin in adults 34-43% SL (Ref. 2), very long (Ref. 1904). Depth of body 40.5-50.5% SL; color-pattern of non-breeding fish and female always including 3 or 4 conspicuous mid-lateral blotches and a red margin on dorsal and caudal fins; breeding male with red margins broader and brighter and general dark, iridescent purplish-brown color of head, back and flanks, masking the blotches; no series of vertical spots or vertical stripes on caudal fin; nest a simple circular depression (Ref. 2).Description: deep bodied (Ref. 12524, 13337, 52307, 54048) with a straight profile (Ref. 1887, 2989, 6465, 12524, 13337, 54048). Snout rounded (Ref. 1887, 2989). Small mouth (Ref. 12524, 13337, 13400), extending to between nostril and eye (Ref. 2989). Lower pharyngeal bone slender (Ref. 54096). Teeth slender, not densely crowded (Ref. 2, 54096), the posterior with a marked second cusp or shoulder; inferior vertebral apophysis only on third vertebra; microbranchiospines present on the outer sides of arches 2 to 4; 5-8 scales between bases of pectoral and pelvic fins; caudal fin only scaled at the base (Ref. 2). Caudal fin with 15 rays (Ref. 1904). Adult large males have the posterior rays of the dorsal fin prolonged (Ref. 12524, 13337). Pectoral fin reaching vertical of origin of anal; pelvic fin reaching between vent and anal; caudal fin rounded; scales cycloid (Ref. 1887, 2989).Coloration: body silvery-grey with upper parts of head and body darker than ventral parts (Ref. 2, 52307). Dorsal fin light green to brown Ref. 12524, 13337). Pectoral (Ref. 1904, 12524, 13337) and pelvic fins light grey ( Ref. 1904) to green; anal fin grey to green at its base (Ref. 12524, 13337). Margins of dorsal and anal fin bright red (Ref. 2, 6465, 7248, 12524, 13337, 52193, 52307). Soft portions of dorsal and anal fins with pale tips and dots (Ref. 2, 1887, 1904, 2989, 6465, 7248, 52193) that are also sometimes visible in the caudal fin (Ref. 2, 52307). 3 prominent black spots present on the flanks (Ref. 2, 1887, 2989, 6465, 12524, 13337, 54048) and a black patch on the posterior portion of the gill cover (Ref. 2, 1887, 2989, 12524, 13337, 54048). The 3 body spots are usually visible from an early age (Ref. 12524, 13337), and are more pronounced in small specimens (Ref. 6465). In breeding males body and fin colours become brighter, with the red seams on the fins becoming more intense (Ref. 2, 7248, 12524, 13337, 52193, 52307) and the snout and cheeks assume a deep maroon coloration (Ref. 12524, 13337, 54048). The caudal fin may appear totally red (Ref. 52307). Juveniles silvery with 6-9 irregular thin bars on body (Ref. 6465, 7248, 12524, 13337, 52193) and 3-4 midlateral spots (Ref. 13337). Young with Tilapia-mark, which disappears or becomes part of the barred pattern of the fin at ca 7cm SL; up to ca 10cm SL vertical bars on the body may predominate and the mid-lateral spots may be faint or absent; 6-10 faint vertical bars appear in dead fish (Ref. 2).
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Ecology

Habitat

Zambezi River Benthopelagic Habitat

This taxon is one of a number of benthopelagic species in the Zambezi River system of southern Africa. Benthopelagic river fish are found near the bottom of the water column, feeding on benthos and zooplankton

Nutrient levels in the Zambezi River are relatively low, especially in the upper Zambezi; in that reach, above Victoria Falls, most of the catchment drains Kalahari sands, whose nutrient levels are inherently low due to their aeolian formation; moreover, agricultural fertilizer addition throughout the Zambezi watershed is low, due to the shortage of capital available to farmers of this region.

Nitrate levels (as nitrogen) in the upper Zambezi are typically in the range of .01 to .03 milligrams per liter. Correspondingly electrical conductivity of the upper Zambezi is on the order of 75 micro-S per centimeter, due to the paucity of ion content. From the Luangwa River downstream nitrate levels elevate to .10 to .18 milligrams per liter, and electrical conductivity rises to a range of two to four times the upper Zambezi levels. Not surprisingly, pH, calcium ion concentration, bicarbonate and electrical conductivity are all higher in portions of the catchment where limestone soils predominate compared to granite.

There are a total of 190 known fish species present in the Zambezi River, including eel and shark taxa. The largest native benthopelagic fish in the Zambezi are the 170 cm North African catfish (Clarias gariepinus), the 146 cm common carp (Cyprinus carpio carpio), the 150 cm Indo-Pacific tarpon (Megalops cyprinoides) and the introduced 120 cm rainbow trout (Oncorhynchus mykiss).

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Kunene River Benthopelagic Habitat

This taxon is one of a number of benthopelagic species in the Kunene River system. Benthopelagic river fish are found near the bottom of the water column, feeding on benthos and zooplankton

The Kunene River rises in the central highlands of Angola, and thence flows southward to form a major element of the border between Namibia and Angola before the final discharge is to the Atlantic Ocean in the vicinity of the Angola-Benguela Front. The geometry of the Kunene riparian zone is distinctly narrow, with rugged arid landscapes persisting on both sides of the river over long distances, and a virtual lack of any extensive floodplains.

There is a relatively high rate of endemism of aquatic biota in the Kunene. Proposed expansion of dams on the Kunene poses a threat to biodiversity in the river, especially regarding proposals at Epupa Falls. However, a greater threat to the Kunene is a plan by Angola to greatly expand withdrawal of water from the river to expand irrigated agriculture by 600,000 hectares; not only will this action significantly diminish downriver flow rates, but also add considerable nitrate, herbicide and pesticide substances to the river.

The catchment area of the Kunene Basin is approximately 106,560 square kilometres (41,143 square miles) in area, of which 14 100 km² (13%) lies within Namibian territory. Its mean annual discharge is 174 cubic meters per second (6145 cubic feet per second) at its mouth on the Atlantic. Water quality of the Kunene River is relatively high, since the human population density and agricultural intensity is relatively low, including a conspicuous absence of overgrazing. However, bacteria and other microbial pathogens pose a material threat to Kunene water quality, due to the fact that only a small fraction of the domestic wastewater in Angola is treated;

Regarding freshwater bivalves, the central reaches of the Kunene manifest particularly high endemism, similar to parts of the Okavango, Chobe, Upper Zambezi and Etosha Pan basins. The bivalve Etheria elliptica, which also occurs in the Upper Zambezi, is a freshwater mussel in the family Etheriidae, known from a limited extent of the central Kunene River in Angola. It is threatened by proposed dam construction on the Kunene.

There are several endemic benthopelagic fishes in the Kunene River: the eight centimeter (cm) long Kunene dwarf happy (Orthochromis machadoi); the 14 cm benthopelagic Namib happy (Thoracochromis buysi); and the seven cm benthopelagic Kunene kneria (Kneria maydelli).

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Habitat and Ecology

Habitat and Ecology
Adults are found mainly in deeper pools and main river channels. Juveniles and sub-adults are found in a variety of habitats in rivers and floodplain lagoons, large open swamps, and, more rarely small tributaries of the rivers. Feeds on detritus, diatoms and zooplankton. Males excavate large, saucer-shaped nests, females mouthbrood the eggs and fry. Multiple broods are raised during the warmer months. Lives for up to 11 years.

Systems
  • Freshwater
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Environment

benthopelagic; freshwater; brackish; depth range 0 - 10 m (Ref. 54002), usually 3 - 6 m (Ref. 54002)
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Depth range based on 2 specimens in 1 taxon.

Environmental ranges
  Depth range (m): 10 - 10
 
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Trophic Strategy

Occurs in both river and swamp habitats (Refs. 2, 6465). Hardy, tolerating fresh and brackish water (up to 20‰, Ref. 3), preferring slow-flowing or standing water (Refs. 7248, 12524, 13337, 52193) with some weed cover (Refs. 12524, 13337). Adults occupy deep open waters (Refs. 7248, 12524, 13337, 52193), juveniles remain inshore among vegetation (Refs. 7248, 52193). Hippo pools are a favoured retreat (Refs. 12524, 13337). Forms schools (Refs. 2, 12524, 13337). Mainly diurnal; a detritivore which feeds on fine particulate matter (Ref. 2), including algae (Refs. 246, 12524, 13337, 53992), diatoms, detritus (Ref. 7248, 52193, 53992) and zooplankton (Refs. 7248, 52193). Larger individuals also take insects and other invertebrates (Ref. 53992). Feeding regime is variable, the diet changes according to food availability (Ref. 6465).
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Diseases and Parasites

Fish Tuberculosis 2. Parasitic infestations (protozoa, worms, etc.)
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Fish tuberculosis (FishMB). Bacterial diseases
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Life History and Behavior

Life Cycle

Spawning did not occur in ponds at a temperature below 21°C (Ref. 2). Rarely more than one brood in a season (Ref. 87, 246), but known to breed at least twice a year under pond conditions (Ref. 12524, 13337). Males excavate saucer-shaped nests (Ref. 246, 2498, 6465, 12524, 13337, 54048) that can be up to 75cm in diameter and 30cm deep, using mouth and fins (Ref. 2, 2498, 52307), in the center of their territory (Ref. 52307), on a sandy substrate (any vegetation is uprooted with its mouth) and in water from 1-3m deep, where they display to attract females (Ref. 12524, 13337, 54048). Up to 40 nests can be found together (Ref. 6465). Females are the primary care-givers (Ref. 52307), moutbrooding eggs, larvae and fry; multiple broods are raised during the warmer months (Ref. 7248, 52193). She lays her eggs in the concavity on top of the nest, the male fertilizes the eggs whereupon the female takes the eggs into her mouth where they are incubated; males guard the nest and females against all intruders; parental care is exercised for the first few weeks after the eggs hatch (Ref. 12524, 13337).
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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage: Oreochromis andersonii

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 13
Species With Barcodes: 1
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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
VU
Vulnerable

Red List Criteria
A3e

Version
3.1

Year Assessed
2007

Assessor/s
D. Tweddle & Marshall, B.E.

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

Contributor/s

Justification
Insufficient data are available on the apparent declines in abundance, but anecdotal evidence suggests a major decline in stocks on the Barotse floodplain since the 1960s as a result of heavy fishing pressure. The rapid spread of alien O. niloticus through the Kafue system will have had a major impact though data are lacking, and the species is now being promoted for aquaculture in the Upper Zambezi catchment. Under criterion A3e, a population reduction of up to 100% is projected in areas where O. niloticus invades. In these area (i.e., in Zambia as a whole), the species should be classed as CR A3(e). It seems inevitable that the O. niloticus will continue to spread throughout the range of O. andersonii unless drastic steps are taken immediately.

At present, the Okavango population is not immediately threatened, but this system is intermittently linked to the Zambezi and thus it is inevitable that O. niloticus will invade the system unless a barrier is constructed across the Selinda Spillway to prevent migration.

O. andersonii is also recorded from the Cunene River, where O. niloticus does not yet occur. The alien species Oreochromis mossambicus (Peters, 1852) is, however, being extensively cultivated in Namibia and may hybridise with O. andersonii if it escapes in to the Cunene.

Establishing refuges in lakes that are not directly connected to the main rivers or to aquaculture establishments may allow small populations to survive. For this reason, and the possibility that the Cunene population may be secure at present, the species is assessed as Vulnerable globally.
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Population

Population
Fairly common and widespread in the Okavango and Upper Zambezi Rivers, although depleted by fishing in some areas such as the Barotse floodplain.

Population Trend
Decreasing
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Threats

Major Threats
The spread of alien Oreochromis niloticus (L.) as a result of aquaculture introductions in the Kafue and Upper Zambezi catchments is a major threat to the survival of O. andersonii throughout its range (Tweddle et al. 2004). Oreochromis niloticus has caused the extinction of O. esculentus (Graham) and O. variabilis (Boulenger) in Lake Victoria. It has also replaced O. mortimeri (Trewavas) in Lake Kariba, has spread throughout the Kafue Flats in Zambia and is rapidly replacing O. mossambicus (Peters) in the Limpopo system in southern Africa.

Increasing fishing effort and increasingly widespread use of small-meshed fishing nets has depleted stocks in many areas, such as the heavily-populated areas of the Barotse Floodplain on the Upper Zambezi River in Zambia. Floodplain lagoons no longer provide refugia as they are all intensively seine netted.

A commercial gillnet fishery in the Panhandle area of the Okavango Delta also targets this species.
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Vulnerable (VU) (A3e)
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Management

Conservation Actions

Conservation Actions
Nile tilapia should be urgently removed from ponds in the Upper Zambezi system in northern Zambia and replaced by O. andersonii. Attempts should be made to prevent the spread of O. niloticus and establish refuges for O. andersonii and other species.
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Relevance to Humans and Ecosystems

Benefits

Importance

fisheries: commercial; aquaculture: commercial; gamefish: yes
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Wikipedia

Oreochromis andersonii

The three-spotted tilapia, Oreochromis andersonii, is a species of cichlid native to Africa, where it is found in rivers and swamps in the southern half of the continent. This species reaches a length of 61 cm (24 in). It is important to local commercial fisheries, as well as being commercially farmed. It is also popular as a gamefish.[2]

References[edit]

  1. ^ D. Tweddle & Marshall, B.E. 2007. Oreochromis andersonii. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>. Downloaded on 7 May 2013.
  2. ^ Froese, Rainer and Pauly, Daniel, eds. (2013). "Oreochromis andersonii" in FishBase. April 2013 version.
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