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Feature

 


Another fish on its way to extinction? 

Dr Ben van der Waal
University of Venda

Nile tilapia hybrid showing most Nile tilapia characteristics from lower Nwanedi River Oct 2001. One of the best known and most esteemed fish species of the lowveld and bushveld, the Mozambique tilapia, also called the blue kurper or bream in Zimbabwe (Oreochromis mossambicus) is now threatened in South Africa. 

The threat does not originate from water pollution or Breeding colours of a Nile tilapia from Zimbabwe. pumping of water out of rivers, but rather from a closely related tilapia species, the Nile tilapia (Oreochromis niloticus). The Mozambique tilapia can be regarded as an endemic fish species of southern Africa as it is distributed naturally only in southern Africa in the Limpopo River system and then all the rivers southwards that are running eastwards as far south as the Bushmans River. It also occurs naturally in the lower Zambezi River below the Cahora-Bassa Dam. As a significant component of the lowveld fish community and important angling fish it deserves to enjoy protection in its native area. But it is now threatened by the Nile tilapia in the Limpopo System, the core area of its distribution range. 

The cause of the threat, the Nile tilapia, is closely related to the Mozambique tilapia and has a natural distribution range including the whole Nile River below Lake Victoria, a few of the lakes of the Rift Valley in Ethiopia, Tanzania and Kenya as well as a few larger rivers of West Africa. Both fish species show similar feeding, breeding, growth and behavioural patterns. Their complimentary natural distribution is a fine example of the so-called "allopatric" distribution found in many closely related species where complete separation between the species has not yet been established. The result is that when man transfers one species into the range of the other, successful hybridisation results. The two tilapia species under discussion have thus never occurred at the same locality together and partly as a result of this, seem not to have developed sufficient mechanisms to prevent hybridisation.

For more information on reasons for the translocation of the Mozambique Tilapia, link here. Enter here for more information.

The Nile tilapia was imported into South Africa in the fifties by the then Cape Nature Conservation Department (!) for breeding and production experiments.  It still exists in a few ponds as well as in some dams in northern KwaZulu-Natal. It is possible that these populations may or have already crossed with the Mozambique tilapia occurring there. The secure refuge of the Mozambique tilapia - its core home, the rivers of the bushveld of the previous Transvaal and southern Zimbabwe and eastern Botswana, are now being invaded by Nile tilapia. It was recorded for the first time in the Limpopo River inside the Kruger National Park in 1996 and then later in 1998 at the confluence of the Limpopo and Shashe Rivers. 

For more information on why Nile Tilapia are being transferred in Africa, link here. Enter here for more information.

A reasonable question an angler or fish farmer could ask is why the possibly superior Nile tilapia should not be promoted and released into dams and rivers in South Africa. All evidence directs at the possibility that it is a better grower and possibly also a better angling fish than the Mozambique tilapia. 

Whilst this may be true, the uncontrolled release of this fish with such a track record would be highly irresponsible - link here to find out why. Enter here for more information.

In order to really protect our Mozambique tilapia, the Nile tilapia would have to be exterminated immediately and completely. That is not possible anymore and the next option now is to inform the public of the imminent threat. Only by concerted efforts by the Department of Environment Affairs and full support of anglers and landowners, will it be possible to keep the Nile tilapia out of certain rivers or sections of rivers in order to conserve the Mozambique tilapia there. In the lower reaches of rivers and dams, no suitable measures are possible. The Department of Environment Affairs should develop effective management plans for all river systems where Mozambique tilapia are found.

Up to now, the Department of environmental Affairs has not taken any action to prevent the spread of Nile tilapia, nor have they declared any catchment a special Mozambique tilapia conservation area. 

Public awareness and help is required to prevent the total disappearance of the Mozambique tilapia. The following action is required to partially curb the negative effects of the unavoidable hybridisation:

1 KNOW WHERE THE PROBLEM IS AND FOLLOW ITS SPREAD
2 INFORM ALL PERSONS DEALING WITH TILAPIA THAT UNDER NO CIRCUMSTANCES MAY ANY LIVE FISH BE TRANSPORTED OR RELEASED WITHOUT THE PROPER PERMITS AND AUTHORITY
3 GIVE PROMINENCE TO OUR OWN INDIGENOUS TILAPIA
4 COMMUNICATE WITH THE LOCAL ENVIRONMENTAL AFFAIRS OFFICE ABOUT THIS NEW THREAT TO OUR INDIGENOUS FISH.


Comparison of external characteristics of Nile and Mozambique tilapia 
NILE TILAPIA MOZAMBIQUE TILAPIA
Prominent vertical bars on tail fin  Tail fin with spots but never in vertical lines
Dorsal fin never red edged, tail end can be red  Tail and especially dorsal fin edged with red
Head and body dark green to silvery grey Head often darker as body, light silver brown to yellowish to blue grey and even black
Eight clear vertical bands on body and tail base  Three unclear spots in a horizontal row on flanks, six or seven unclear vertical bands on body
Spines of dorsal fins long, very thick and prominent  Anal and dorsal fin spines well developed but never thickened
Dorsal and anal fins relatively high compared to body depth Dorsal and anal fins not prominently high as in the Nile tilapia
Eye typically red coloured  Eye from yellow to dark brown, never red
Males in breeding dress with a pinkish head and body and tail fin Males in spawning dress very dark to black with a white chin, with prominent red edge to dorsal fin
Males never have a prominent enlarged mouth and concave profile of the snout  Males often with enlarged mouth and concave head profile
A simple differentiating test between the two species is a count of the lower branch of the first gill arch. This can easily be done by lifting the gill cover and counting the rakers or teeth on the lower (larger) half of the gill. 
20 to 26 gill rakers 16 to 20 gill rakers



 

Dr Ben van der Waal
Department of Biological Sciences
University of Venda
PO Bag X 5050
THOHOYANDOU 0950

bcw@univen.ac.za



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