Anthropic effects on the fish community of Ribeirão Claro, Rio Claro, SP, Brazil

Abstract

The effect of anthropic alterations such as drain discharge on a fish community was studied in the Ribeirão Claro River, municipality of Rio Claro, State of São Paulo, southeastern Brazil. Samples were made monthly in three different points along the river (headwaters, mid course, and confluence) between December, 2003 and March, 2004, which is the reproductive period for the majority of the species. The fish community of the Ribeirão Claro River showed a fair composition and diversity, with species rarely observed in studies made in the region, such as Paravandellia oxyfera and Callichthys callichthys. Indices of diversity and equitability showed different results when weight or the number of individuals were considered. Moreover, these indices did not reveal the typical increase in diversity from the headwaters toward the confluence, nor the loss of richness in the part altered by drain discharge. An interpretation should be made with caution, taking into account the diverse factors included in the computation. Similar to the diversity indices, the Morisita-Horn similarity index did not reveal a great difference in the fish community of the confluence of the river, mainly in relation to its mid course. The decline of species richness and trophic composition alteration in the disturbed part is clear, which shows a great dominance of piscivorous species.Keywords: diversity indices, freshwater fish community, pollution effects, Ribeirão Claro, Brazil. Efeitos antrópicos na comunidade de peixes do Ribeirão Claro, Rio Claro, SP ResumoCom o objetivo de verificar o efeito de alterações antrópicas, como o despejo de esgotos sobre a comunidade de peixes do Ribeirão Claro, SP, foram feitas coletas mensais em três pontos ao longo do rio (cabeceira, meio e foz) entre dezembro de 2003 e março de 2004, período reprodutivo para a maioria das espécies da região. O Ribeirão Claro apresentou boa composição e variedade em sua comunidade íctia, possuindo espécies raramente observadas em trabalhos na região, como Paravandellia oxyfera e Callichthys callichthys. Os índices de diversidade e equitabilidade apresentaram diferentes resultados quando considerado o peso ou número de indivíduos, além de não evidenciarem o comportamento típico de aumento da diversidade no sentido cabeceira-foz, nem a conseqüente perda de riqueza taxonômica no trecho impactado pelo despejo de esgoto doméstico. Sua interpretação deve ser feita com cautela, considerando os diversos aspectos incluídos em seus cálculos. Assim como os índices de diversidade, a similaridade de Morisita-Horn não ressaltou a grande diferença na comunidade da foz do Ribeirão Claro, em especial com relação ao trecho médio do rio. Fica evidente o declínio na riqueza de espécies no trecho poluído e a alteração em sua composição trófica, apresentando alta dominância de espécies piscívoras.Palavras-chave: Índices de diversidade, comunidade de peixes de água doce, efeitos da poluição, Ribeirão Claro, Brasil.

Trophic ecology of the ichthyofauna of a stretch of the Urucu River (Coari, Amazonas, Brazil)

“…In the studied area the diversity values obtained can be considered high, considering that index values above 3.0 indicate high diversity (Goulding, 1980). Corroborating our results, Kushlan (1976), Saint-Paul et al (2000), Casatti (2006), Cunico et al (2006), Ferreira and Petrere (2007), Silva (2008) and Correa (2008) found higher values of taxonomic diversity in the flood season. The dynamics of flooding promotes increased production and high diversity of fishes, and this plays an important ecological role in the whole basin (Silva et al, 2007).…”

An ecologically constrained procedure for sensitivity analysis of Artificial Neural Networks and other empirical models

“…However, species richness was also affected by variables that convey information about some relevant local conditions, like habitat features, hydrologic factors or urbanization. As a matter of fact, several studies evidenced that, at local scale, urbanization and/or flow regulation may strongly modify the expected fish species richness [40], [47]. Results obtained from the constrained sensitivity analysis showed indeed how, at any given site, fish species diversity is highly affected by environmental factors as habitat descriptors (e.g.…”

Changes in the structure of fish assemblages in streams along an undisturbed-impacted gradient, upper Paraná River basin, Central Brazil

“…An increase in sediments diminishes the diversity and integrity of aquatic communities, thus upsetting the availability of fish shelters which serve as protection against birds and mammal predators or are used for feeding and spawning (Berkman & Rabeni, 1987). Domestic effluent deposited in the water diminishes the water oxygen content (Smith & Barrela, 2000;Daniel et al, 2002;Ferreira & Petrere-Jr., 2007) thereby killing certain organisms or benefiting others, such as those of Poecilia reticulata (Lewis Jr., 1970;Poulin et al, 1987;Vieira & Shibatta, 2007;Casatti et al, 2006a,b).…”