Cesar Enrique de Melo

Feeding habits of fish from a stream in the savanna of Central Brazil, Araguaia Basin

The objective of the present study was to determine the composition of the diet of fish and its relation to the condition of canopy along a stream in the savanna of Central Brazil. Fish were collected monthly from April 1994 to March 1995. A total of 3872 individuals belonging to 82 species were captured and 1606 of them had their stomach content analysed. Allochthonous resources were widely used by fish. Although some fish groups do present generalist habits, most of the species can be included in well-defined trophic groups. Piscivores were abundant only during the flooding season when they occupied the stream looking for food and reproduction sites. Deforestation of the riparian forest has negative effects on the fish populations that depend on allochthonous resources. Lack of vegetation near the mouth of the river allows sand accumulation on the bottom of the stream and destruction of important microhabitats used as feeding and shelter, a fact that excluded some species from this site.

Alimentação e distribuição de piaus (Pisces, Anostomidae) na Planície do Bananal, Mato Grosso, Brasil

The Anostomidae fishes are restricted to South America, and they are economically important to fisheries in many regions. Studies conducted in Central Amazon, where they are widely distributed, demonstrated that these fishes have high feeding plasticity. In this study we analyzed nine species of Anostomidae and we discussed ecological interactions in relation to their feeding and distribution in the Planicie do Bananal, a Cerrado region which is subject to periodic floods and it is drained by Araguaia/Tocantins basin. Niche breadth was low among the six species analyzed (0,125 and 0,355). Schizodon vittatum (Valencienes, 1894) has the widest niche breadth and it is also the most widely distributed species. Qualitative analyses comparing species feeding among habitats demonstrate great variation in the proportion of ingested items from one environment to another, while quantitative analyses show relatively higher similarities. Laemolyta petiti Gery, 1964 and Laemolyta taeniata (Kner 1859) are the most specialized species in relation to ingested items, as well as the proportion of each item founded in the stomach contents.

Relationships between water transparency and abundance of Cynodontidae species in the Bananal floodplain, Mato Grosso, Brazil

The Cerrado in the Central Brazil is currently one of the most threatened ecosystems in the world. As a result, the aquatic habitats in this biome also undergo great impacts. Alterations related to land-use change increase sediment loadings in rivers, streams and lakes, resulting in sedimentation and decrease in water transparency. Water transparency determines underwater visibility conditions, and as a consequence fish assemblages respond to spatial and temporal changes in this variable. This work aimed to examine the influence of transparency on the abundance and distribution of Cynodontidae species, a visually oriented predatory fish group. Fish sampling was conducted in 15 sites located between Mortes and Araguaia rivers in the Bananal floodplain, Mato Grosso State. Regression analysis between relative abundance of Cynodontidae (in number of individuals and biomass) and water transparency showed a positive and highly significant correlation, indicating that this group shows species-specific habitat affinities for clearer waters. These results suggest that the increase in water turbidity in this region can affect the patterns of abundance and distribution of the Cynodontidae species, as well as other visually oriented fishes.

Influence of environmental parameters on fish assemblage of a neotropical river with a flood pulse regime, Central Brazil

Este estudo determinou quais entre doze parâmetros ambientais (cinco fisico-quimicos e sete hidromorfologicos) influenciam na estrutura da assembleia de peixes do baixo rio das Mortes localizado na planicie de inundacao do Bananal, bacia do rio Araguaia, Brasil Central. As coletas foram realizadas em seis trechos de 1000 m cada durante os periodos de chuva e estiagem, nos quais 1036 peixes foram coletados utilizando-se redes de malhar e medidos os parâmetros ambientais utilizando equipamentos portateis ou determinados visualmente. A analise de coinercia indicou que dois parâmetros fisicos e quimicos (oxigenio dissolvido e a transparencia da agua) e quatro hidromorfologicos (largura e profundidade da calha principal, cobertura da mata riparia e tipo de substrato da margem) estruturam a assembleia de peixes, ambos influenciados pelo regime hidrologico regional (pulso de inundacao). Estes resultados sao discutidos considerando a interacao entre peixes e os parâmetros ambientais caracteristicos dos sistemas aquaticos Neotropicais.

Diversidade biológica da comunidade de peixes no baixo rio das Mortes, Mato Grosso, Brasil

The das Mortes River is one of the main water courses of the Mato Grosso State and the largest tributary of the Araguaia River on it’s left bank. Its low section is located in the Bananal floodplain. This study aims to characterize the fish assemblage of this river during high and low waters. Fish assemblage during low waters was characterized by high diversity (4.783 bits/individuals of the Shannon-Wiener index), species richness (69 species sampled) and abundance (659 individuals), where the most abundant species were Pygocentrus nattereri Kner, 1858 and Boulengerella cuvieri (Agassiz, 1829). Ageneiosus inermis (Linnaeus, 1766) and Rhaphiodon vulpinus Agassiz, 1829 were abundant at high waters. Interaction between the fish assemblage and the floodplain have similar pattern to that observed in other Neotropical floodplains.