RESUMO

The present study catalogues exotic and allochthonous fish species found in the three main freshwater river drain-ages of Rio Grande do Sul State using records of scientific collections and literature, and discusses the main impacts caused by their introduction in natural environments. Ten exotic species are found in the area, i.e., Clarias gariepinus, Coptodon ren-dalli, Ctenopharyngodon idella, Cyprinus carpio, Hypophthalmichthys molitrix, Hypophthalmichthys nobilis, Ictalurus punctatus, Micropterus salmoides, Oncorhynchus mykiss and Oreochromis niloticus, belonging to five orders, nine genera and seven fami-lies. These fishes are native from African, Asian, European and North American countries. The eight allochthonous species, i.e., Acestrorhynchus pantaneiro, Hoplerythrinus unitaeniatus, Hoplias lacerdae, Megaleporinus macrocephalus, Piaractus mesopota-micus, Pachyurus bonariensis, Serrasalmus maculatus, and Trachelyopterus lucenai, belong to three orders, eight genera, and six families, are native from the Río La Plata basin, that includes the Río Uruguay, and have been all registered in the Laguna dos Patos. Two of these species are further recorded in the Rio Tramandaí system (A. pantaneiro and T. lucenai). The study also pre-sentes a brief history of the first records of exotic species in the state and in the country, and their main vectors of introduction. According to the records of exotic species in scientific collections, the two exotic species with the highest number of records in the country are tilapias Coptodon rendalii (508 records) and Oreochromis niloticus (376 records), and most records occurred in the last two decades. The two carps Cyprinus carpio and Ctenopharyngodon idella are the only exotic species recorded in the three main drainage basins of the state. In addition, we warn about the importance of studies about the biology and negative impacts of exotic species over native species on the understanding of management in wild environments.(AU)

Assuntos

RESUMO

Some aspects of reproduction in two species of Mimagoniates, M. microlepis (Steindachner 1877) and M. rheocharis Menezes & Weitzman 1990 are herein described. Samples were taken monthly from January 1998 to February 1999 in two streams in the locality of Maquiné, Rio Grande do Sul, Brazil. Results from the analysis of hundreds of specimens of M. microlepis and M. rheocharis in two investigated sites indicated mature specimens and peaks of the gonadosomatic index (GSI) along the year. There was a negative and significant correlation between M. microlepis males GSI and water temperature. Females of the latter species and both sexes of M. rheocharis, in turn, showed no correlation with any of the tested parameters (relative stomach weight, day length, rainfall). Absolute and relative fecundity are lower than in externally fertilized species of Characidae. Maximum oocyte length was 1.14 mm for M. microlepis and 1.02 mm for M. rheocharis and both species were characterized as total spawners based on the type of oocyte development estimated through oocyte size analysis. Features like non-seasonal reproductive period, low fecundity, and insemination may indicate adaptive advantages, which may enhance the chance of survival even with low energetic investment and improved fertilization.(AU)

Assuntos

RESUMO

Some aspects of reproduction in two species of Mimagoniates, M. microlepis (Steindachner 1877) and M. rheocharis Menezes & Weitzman 1990 are herein described. Samples were taken monthly from January 1998 to February 1999 in two streams in the locality of Maquiné, Rio Grande do Sul, Brazil. Results from the analysis of hundreds of specimens of M. microlepis and M. rheocharis in two investigated sites indicated mature specimens and peaks of the gonadosomatic index (GSI) along the year. There was a negative and significant correlation between M. microlepis males GSI and water temperature. Females of the latter species and both sexes of M. rheocharis, in turn, showed no correlation with any of the tested parameters (relative stomach weight, day length, rainfall). Absolute and relative fecundity are lower than in externally fertilized species of Characidae. Maximum oocyte length was 1.14 mm for M. microlepis and 1.02 mm for M. rheocharis and both species were characterized as total spawners based on the type of oocyte development estimated through oocyte size analysis. Features like non-seasonal reproductive period, low fecundity, and insemination may indicate adaptive advantages, which may enhance the chance of survival even with low energetic investment and improved fertilization.

Assuntos

RESUMO

Reproduction of Bryconamericus stramineus was described based on the analysis of 208 females and 166 males collected monthly in the Rio Ibicuí, from April 2001 through March 2002. Reproduction occurred between September and December, with a lower peak in February. The mean absolute fecundity was 371.3 (± 244.6) oocytes and the mean relative fecundity was 0.35 (± 0.08) oocytes/mg of total weight and the fish was a multiple spawner. A weak correlation between GSI of males and day length was observed. Other parameters (stomach repletion and hepatosomatic index, rainfall and temperature) did not show any correlation with GSI. However, some of these factors might act as "starters" of gonadal maturation. The presence and frequency of fin ray hooks on the males was compared with the gonadal maturation stages, months and standard length classes. Well-developed hooks were found mainly in the mature males during the reproductive period and in the largest individuals.

A reprodução de Bryconamericus stramineus é descrita baseada na análise de 208 fêmeas e 166 machos coletados mensalmente no rio Ibicuí, RS, de abril/2001 a março/2002. A reprodução ocorreu entre setembro e dezembro, com um pico menor em fevereiro. A fecundidade absoluta média é de 371.3 (± 244.6) ovócitos e a fecundidade relativa média é de 0.35 (± 0.08) ovócitos/mg de peso total e a espécie tem desova parcelada. Foi observada uma fraca correlação entre IGS de machos e fotoperíodo; os índices de repleção estomacal e hepatossomático, a pluviosidade e temperatura não mostraram nenhuma correlação. Porém, sugerimos que alguns destes fatores possam agir como "desencadeadores" da maturação gonadal. A presença e freqüência de ganchos nas nadadeiras de machos foi comparada com as fases de maturação gonadal, meses e classes de comprimento padrão. Ganchos bem-desenvolvidos foram encontrados principalmente em machos maduros, durante o período reprodutivo e nos indivíduos maiores.