Exotic and allochthonous species from the Paraíba do Sul River basin: implications for conservation

Abstract

Introduction of species, intentional or accidental, is one of the major causes of alteration in the natural distribution of organisms, provoking serious population decline of native species. Exotic species of fishes were introduced in Brazil since the 1940's, aimed mostly at the development of aquiculture in the country. Species translocations from a river basin to another also occurred, primarily from the Amazon River basin to other Brazilian regions. One of the negative effects of species introduction is related to the genetic patrimony of natural populations, with the possibility of occuring hybridization that decrease natural genetic variability. This can result in the emergence of fertile hybrids, threatening the parental stock for medium to long term. Other negative ecological effects are the potential introduction of pathogens, structural changes in trophic webs and potential depletion of native populations by competition or predation. In view of the importance of this issue and its effects in freshwater environment, a list of invasive species of the Paraíba do Sul river basin, southeastern Brazil, is presented. Sixty-two species of fishes were recorded, with a predominance of the Cichliformes, Characiformes and Cypriniformes, three bivalve mollusk species and three species of a decapod crustacean. Many of the invasive fish species are reared in pisciculture tanks in the region, being introduced by eventual escapes or direct releases, due to great interest of sport and amateur fishing. Other species are hybrids of invasive and native fish species, such as the tambacu (Colossoma macropomum x Piaractus mesopotamicus) and pintachara (Pseudoplatystoma corruscans x P. fasciatum). Other introductions result from aquarium activities, with records of established populations of fishes and mollusks, and the crayfish Procambarus clarkii. Bivalve mollusks were introduced by ballast water of ships. The Malaysia Giant crustacean (Macrobrachium rosenbergii) was introduced for aquaculture in the 1980's, and has been recorded in the basin occasionally. In addition to this, an allochthonous species of shrimp,
M. jelskii, is also recorded in Paraiba do Sul river basin. The golden dorado Salminus brasiliensis, in turn,
occurs all over the basin, with populations established since long ago. There are few eradication programs
for invasive species in Brazilian waters, and the encouragement of directional fishing of invasive species may be an alternative, even though environmental biotic integrity might not be reestablished after eradication
of the invader. For non-native species from aquarium and sport fishing, there are recent suggestions to
prevent/reduce invasion. Monitoring the non-native aquatic fauna is recognized as extremely important in
both predicting and trying to avoid its dispersion.