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.

Farmer's Weekly (South Africa) - - Contents - by ni­cholas james Ni­cholas James is an ichthy­ol­o­gist and hatch­ery owner. Email him at farm­er­[email protected]­ton.co.za. Sub­ject line: Aqua­cul­ture. BE­LOW: FW

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 (LKeller­[email protected] 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

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