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International Waters: Breeding of Non-native Fish Could Spell Disaster

Posted: September 10, 2013, 10:30 a.m. EDT

By John Dawes

Non-native invasive species continue to make headlines of the negative kind, but Brazil appears to be on the verge of implementing measures that could facilitate the establishment of non-native fish species in its waters. Such a plan moving forward could spell disaster, not just for some native fish species, but also for those whose livelihoods depend on such fish. Prominent among these are the ornamental fish collectors who supply the worldwide trade and hobby.

Non-Native Species
The Xingú river ray (Potamotrygon leopoldi) is one of several species in Brazil that are being affected adversely by hydroelectric power station projects, with at least one species (but possibly more) being driven to the point of extinction. John Dawes

Some of these livelihoods already are under threat as a result of the dams that accompany the construction of hydroelectric power stations in Brazil. A frequent consequence of these major projects, such as the huge dam being built at Belo Monte on the Rio Xingú, is the loss of habitats of iconic species such as the zebra pleco (Hypancistrus zebra). Its only known habitat is the Volta Grande (Big Bend) on the Rio Xingú, which already is being irrevocably and dramatically modified; the inevitable outcome is that the species will be driven to extinction in the wild.

There is absolutely no way of preventing this from happening, other than by calling a halt to the construction, which is not going to happen.

Besides mourning the unnecessary loss of a beautiful species in the wild, one of the reasons I mention this example (there are more species under threat—see footnote) is that no preventive measures to create a breeding program for this species—or for any of the others affected by the dam—have been implemented, with the result that no zebra plecos at all are being bred in Brazil itself.

The centers of this activity are in the Far East, where freshwater stingrays (which can only be collected under quota in Brazil) also are being bred in considerable numbers. Many species of freshwater ornamental fish cannot be exported from Brazil because they are classified as food fish (among them the oscar—Astronotus ocellatus), and it’s easy to see how the Brazilian ornamental aquatic sector is experiencing increasing pressure and is at a disadvantage with its competitors, who are only too willing to fill the gaps left by each restriction, ban or loss of habitat and species.

And so it is likely to be the case if the latest moves are implemented, according to a group of scientists headed by Angelo Agostinho of the State University of Maringá in Paraná. They argue that if Projeto de Lei 5.989/09 goes ahead it could lead to the naturalization of some of the most invasive species in the world, such as tilapia and carp.

The scientists’ claim arises from the fact that the new law would allow the rearing of non-native fish in cages within any hydroelectric reservoir in the country. According to the authorities, who say the country possesses immense lakes where fish can be produced, the aim of the exercise is to generate income for those living in areas surrounding reservoirs, where local fisheries have collapsed following the construction of dams.

The authorities believe the scientists’ concerns are exaggerated and that tilapia and other species already are present in the country’s waterways. They also believe there is a solution: the production of single-sex stocks. The scientists argue there are always individual specimens that change sex. Irrespective of this, non-native species alter the environment and the composition of the local fauna and flora.

Although the final decision regarding approval of the Projeto hasn’t been made, and although the choice of species that will be permitted for the breeding programs will eventually rest with the Ministry of Fisheries, an earlier draft gave good reason for concern. Among the species originally listed were the Nile tilapia (Oreochromis niloticus), the common carp (Cyprinus carpio), the silver carp (Hypophthalmichthys molitrix) and the grass or Asian bighead carp (Ctenopharyngodon idella). The scientists also believe that other species that could end up being approved could include the channel catfish (Ictalurus punctatus) and several predatory African cats, such as the Clarias species.

The proposal already has been through three committees and is awaiting the final decision by the Brazilian senate. In the meantime, the Brazilian ornamental aquatic sector must be bracing itself for what will amount to yet another heavy blow.

The zebra pleco is not the only fish facing extinction as a result of the Belo Monte dam. Other species much admired and sought after in the trade and hobby include the magnum, orange seam or mango pleco (Baryancistrus chrysolomus), the gold nugget pleco (B. xanthellus), the king tiger pleco Hypancistrus sp.), the scarlet pleco (Pseudacanthicus sp.), the royal pleco (Panaque aff. armbrusteri) and the goldie, or sunshine, pleco (Scobinancistrus aureatus). The impressive Xingú river ray Potamotrygon leopoldi), which is being wildly bred in Asia, also is found in this region.



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