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Implication Of The Presence Of Nile Tilapia In The Limpopo River
- The probability that the Nile tilapia will hybridise with the Mozambique tilapia is great. That means that everywhere these two fishes occur together, hybrids with mixed characteristics will result after some time.
- The Mozambique tilapia is now vulnerable in its own distribution range and may become a threatened species. The presence of the Nile tilapia in the Limpopo will make it possible to enter and migrate into the lower reaches of the Levuvhu, Olifants, Nzhelele, Nwanedi, Sand, Magalakwin, Mogol, Matlabas, Crocodile , Marico and more rivers.
- 3 Nile tilapia will possibly be prevented [temporary] to pass over dam walls and higher
weirs and migrate higher up into a river - until an overzealous angler transfers the fish into the dam. It will then colonise a dam, hybridise and migrate further upstream.
- Anglers and/or fish farmers will in time illegally distribute the Nile tilapia to all river systems south of the Limpopo. Nile tilapia will then have the opportunity to invade all river systems where Mozambique tilapia are found.
- It will later not be possible to determine the tilapia species caught by anglers. All records for Mozambique tilapia [or Nile tilapia] will thus be doubtful, except when electrophoretic studies are undertaken.
- Pure Mozambique tilapia will only be located in isolated and separated upper streams and tributaries that are separated from the rest of the river systems by high, insurmountable walls. It is also known that this fish is not usually found in higher areas. Many of these higher tributaries do thus not offer permanent or ideal habitat for this species. Genetic deterioration may then become a new problem in these isolated populations.
- Other temporary safe refuge areas for the Mozambique tilapia are the smaller rivers of the east-flowing rivers of KwaZulu/Natal that have their own catchments and are not connected to larger rivers. Even here the tilapia are not really safe because the sea offers a possible connection to the hybrid. Anyway, the uncontrolled transfer of only a few fish into a river system will eventually infect a whole system.
- There is another (smaller) possibility that the Nile tilapia will not (or not everywhere) cross with our Mozambique tilapia. Then it must be expected that because these two species are so similar in their habits, strong competition will develop, resulting in the eventual disappearance of the weaker species. Evidence from Africa, including Lake Victoria and dams in Madagascar and Indonesia indicate that the Nile tilapia is the more aggressive species. This implies the complete or partial disappearance of the Mozambique tilapia from rivers in South Africa.
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