A recent review paper on the African sharptooth catfish (Clarias gariepinus) has highlighted the urgent need for
impact studies. The paper, published in the Journal
of Fish Biology, was a collaboration between C·I·B researcher Olaf Weyl and Bruce Ellender from the
South African Institute for Aquatic Biodiversity (SAIAB), and Jean Vitule and Vanessa
Dagaa from the Universidade Federal do Paraná, Curitiba, Paraná, Brazil.
Recent invasions of rivers in Brazil, China, India and South Africa by African sharptooth catfish are worrying because this
large predator is likely to have negative impacts on local ecosystems. African sharptooth catfish also have traits that not only make them highly
invasive but also make them the ideal species for fish farming (aquaculture). For example, the species can cope with a wide range of environmental
conditions e.g. water temperatures between 8-35°C, can survive in brackish water, can breathe air, withstand periodic desiccation and can
“walk” over land. They grow quickly, are highly fecund and can live for up to 35 years.
Its importance in the global aquaculture industry has resulted in its introduction into more than 60 countries. As fish farming is
an important economic activity, decision makers will need to weigh-up potential impacts on biodiversity against economic gain when planning
mitigation measures. For this reason, understanding the invasion process is crucial for the development of management approaches for this invader
and a possible Conflict Species.
The review highlighted that despite South Africa and Brazil being instrumental in the development of African sharptooth catfish
aquaculture, production of this species all but collapsed within 5 years of initiation. However, after initial introductions across geographical
barriers, containment seems to have been impossible and escape from aquaculture facilities is an invasion pathway in both countries.
Assisted by illegal stocking by anglers, this species can be categorised as fully invasive in both countries “with
individuals dispersing, surviving and reproducing at multiple sites across a greater or lesser spectrum of habitats and extent of occurrence”
(See Blackburn et al., 2011).
“Impact studies are urgently needed to better understand the consequences of these invasions and to develop appropriate
strategies for mitigation,” says Weyl. Highlighting the need for impact studies, he adds, “impact studies are particularly
relevant as future development of fisheries and aquaculture in the two countries may well result in further invasion opportunities and conflicts
between fish farmers and conservationists.”
Read the paper by Weyl et al.
Weyl, O. L. F., Daga, V. S., Ellender,
B. R. and Vitule, J. R. S. (2016), A review of Clarias gariepinus invasions in Brazil and South Africa. Journal of Fish
C·I·B core team member Olaf Weyl holding an African sharptooth catfish (Clarias
gariepinus). African sharptooth catfish is a large predator, reaching up to 1.7 meters in length and weights of 60kg.
(Photo credit: Olaf Weyl)