Ana Paula Sassanovicz Dufech

Comparative dietary analysis of two populations of Mimagoniates rheocharis (Characidae: Glandulocaudinae) from two streams of Southern Brazil

The diet of two populations of Mimagoniates rheocharis, from two freshwater streams of the rio Tramandai, northeastern Rio Grande do Sul, Brazil, are described and compared. The specimens were collected monthly from January 1998 to March 1999, with dip nets and seine nets and preserved in 10% formalin. In laboratory, the standard length of each specimen was measured. The stomachs were removed and dissected for identification of the alimentary items. The data were analyzed using the frequency of occurrence, percent composition and index of alimentary importance methods, being the last two compared among different classes of standard length. Three methods of analysis showed the highest values for allochthonous insects, regardless the locality of collection or body size of the specimens.

Biologia populacional de Pachyurus bonariensis Steindachner, 1879 (Perciformes, Sciaenidae), uma espécie alóctone no sistema hidrográfico da laguna dos patos, Brasil

The genus Pachyurus is widely distributed in the large hydrographic systems of South America, being represented only by Pachyurus bonariensis in the southern portion of the continent, in the La Plata drainage (Uruguay, Parana and Paraguay rivers). The occurrence of this species is recent in the Laguna dos Patos system, and most aspects about population biology and distribution of P. bonariensis for this region are unknown. Abundance, constancy of occurrence, sexual dimorphism and sex ratio were analyzed for the species. The establishment of this species in the Laguna dos Patos system is discussed. One hundred and one specimens (82 females, 15 males and four immature) were captured in the Parque Estadual de Itapua, Rio Grande do Sul State, at Praia das Pombas, Lago Guaiba. The species was constant during the studied period, from June 2002 to July 2003. The abundance was higher in January and April 2003. Females were larger and significantly more abundant than males (c2 = 43.12; p < 0.05). These results and the identification of sexually mature females suggest reproductive activity and indicate that P. bonariensis is an allochthonous species that established a successful population in the Laguna do Patos hydrographic system.

Feeding habit of Eigenmannia trilineata Lopez & Castello, 1966 (Teleostei: Sternopygidae) of Parque Estadual de Itapuã, RS, Brazil

This study aims to describe the feeding habits of a population of the weakly electric fish Eigenmannia trilineata from Southern Brazil through the monthly frequency variation of replection (RI) and hepatosomatic (HSI) indexes, condition factor (CF) and dietary analysis of the species, besides the comparison of the results with abiotic factors. We collected 428 specimens from June/2002 to May/2003 with a dip net and electric fish detector. Stomach contents were analyzed using three measurements: frequency of occurrence of food items, percentage composition per prey type and feeding importance index. Microcrustacea and autochthonous insects were the dominant food items in the stomachs of E. trilineata. The adults (males larger than 63.5 mm and females larger than 80.5 mm) exhibited little alteration in their diet during the reproductive period and ingested more variety of food items. The RI of males, but not females, showed peaks before and after the reproductive period, having significant correlation with the HSI. Condition factor was more influenced by stomach weight in males and by the gonad weight in females. No correlation between abiotic factors and feeding activity was identified. Este estudo objetiva descrever o habito alimentar de uma populacao da especie de peixe eletrico Eigenmannia trilineata do Sul do Brasil, atraves da variacao das frequencias mensais dos indices de replecao (IR), hepatossomatico (IHS), fator de condicao (FC) e analise da dieta da especie, alem da comparacao dos resultados obtidos com fatores abioticos. Foram coletados 428 exemplares entre os meses de junho/2002 e maio/2003 com o auxilio de rede do tipo puca e um detector de peixe eletrico. Os conteudos estomacais foram analisados utilizando tres metodos de mensuracao: frequencia de ocorrencia de itens alimentares, composicao percentual por tipo de presa e indice de importância alimentar. E. trilineata apresentou microcrustaceos e insetos autoctones como alimentos principais. Os adultos (machos maiores que 63,5 mm e femeas maiores que 80,5 mm) tiveram pequena alteracao em sua dieta durante o periodo reprodutivo e ingeriram uma maior variedade de itens do que os juvenis. O IR dos machos apresentou picos antes e depois do periodo reprodutivo, obtendo correlacao significativa com o IHS, fato este nao verificado para as femeas. O fator de condicao foi mais influenciado pelo peso do estomago nos machos e das gonadas nas femeas. Nao foi identificada correlacao entre fatores abioticos e a atividade alimentar da especie.

Estudo comparado da taxocenose de peixes em dois ambientes aquáticos do Parque Estadual de Itapuã, sul do Brasil

This paper characterizes and compares the taxocenoses of fish from two different aquatic environments within a basin hidrographyc: the Praia das Pombas (Lago Guaiba) and the Lagoa Negra, both in the Parque Estadual de Itapua, Rio Grande do Sul, considering quali-quantitative composition of the ichthyofauna. Ecological and abundance indexes were evaluated in both spatial and temporal contexts, checking that occurs relationship between the structure of taxocenose these sites with environmental variables. We sampled a total of 61 species, with the richness the same in both locations (44 species). Both environments showed peculiar characteristics that reflected on the fish fauna in each location. It was observed that the pattern of distribution of the taxocenoses of fishes studied in the two environments is seasonal, since the abundance, biomass and diversity were higher in the hottest months of the year, spring and summer. The temperature and day-length the main factors that influenced in the distribution of the fish fauna of the Praia das Pombas and Lagoa Negra.