Perspectives in Aquaculture

Although developed strains of Nile tilapia exist in South Africa, the species sparks fierce debate. To help with planning and conservation, scientists must know how far the species has spread.

The presence of Nile tilapia ( Oreochromis niloticus) in South Africa is a contentious one, with strong views on both sides. The basic facts are these:

• Farmers, whether they produce maize, cattle or fish, select the optimal strain to achieve economic success;

• In aquaculture, Nile tilapia is the species of choice, and there are developed strains with faster growth, greater disease resistance, and much improved yield. These advantages are not marginal, as claimed by some, but are the difference between success and failure. World production of over three million tons of tilapia is evidence of this.

Nile tilapia is indigenous to North, West and East Africa. It has been widely distributed in Zimbabwe and Mozambique for aquaculture, with none of the conservation restrictions that apply in South Africa. Escapees in these countries have hybridised with the indigenous tilapia species O. mossambicus (blue kurper) and O. mortimeri (Kariba tilapia). Clearly, this is an environmental concern.

The first Nile tilapia to appear in South Africa were collected 20 years ago in the Limpopo catchment and the species has since spread up the large Lowveld rivers shared with neighbouring countries. This was predictable, as O. niloticus can tolerate a water temperature as low as 12°C, which means that most low-altitude rivers in the north and east are vulnerable to upriver invasion.

Aquatic scientist Dr Ben van der Waal warned the provincial offices of the Department of Environmental Affairs (DEA) that this would happen. But his warnings, even those calling for sanctuary establishment for our blue kurper, were ignored.

At the same time as this quiet invasion, three provincial DEA offices, namely Limpopo, Mpumalanga and KwaZuluNatal, banned all aquaculture systems in their provinces from using Nile tilapia, believing this would somehow hinder further spread of the species.

a scientist’s calls for blue kurper sanctuaries were ignored

The aquaculture community has requested that the DEA’s Alien Invasive Species Directorate permit farming with Nile tilapia in catchments where the invasion is proven and irreversible. The DEA agreed to survey the extent of the invasion, with a commitment from the directorate and the provincial DEA offices that refusal of permits in invaded catchments be scrapped.

Delays in contracting and funding have resulted in no surveys to date. However, university-based research in KwaZuluNatal indicates that few pure populations of O. mossambicus remain, and that even

O. aureus (blue tilapia) is present. This Israeli tilapia species was introduced by the DEA during the 1960s and stocked in several water bodies in the north of the province before the hybridisation threat was understood.

help requested

An urgent appeal is made to the public to assist in data collection this summer to ascertain the extent of Nile tilapia invasion. Anglers and landowners are requested to catch juvenile or adult tilapia from any water body, photograph them with the tail fin extended, and send the photographs and locality details to myself or Lizande Kellerman (LKellerman@csir. co.za) at the Council for Scientific and Industrial Research for identification.

Both aquaculture development and the establishment of sanctuaries can then be based on sound information.

To assist in research, anglers are requested to catch and photograph tilapia with the tail fin extended. nicholas james