Abstract
We assessed the trophic structure of the fish fauna in Sinhá Mariana pond, Mato Grosso State, from March 2000 to February 2001. The aim was to determine the feeding patterns of the fish species during the rainy and dry seasons. The diets of 26 species (1,294 stomach contents) were determined by the volumetric method. Insects and fish were the most important food resources: insects were the dominant food of 23% and 27% of the species, respectively, in the rainy and dry season, and fish was the dominant item for 31% of the species in both seasons. Cluster analysis (Euclidean Distance) identified seven trophic guilds in the rainy season (detritivores, herbivores, insectivores, lepidophages, omnivores, piscivores and planktivores), and five trophic guilds in the dry season (detritivores, insectivores, lepidophages, omnivores and piscivores). The smallest mean values of diet breadth were observed for the specialist guilds (detritivores, lepidophages and piscivores), in both seasons. The widest means for diet breadth were observed for the omnivores, regardless of the season. In general, there was no seasonal variation in feeding overlap among the species studied. At the community level, diet overlap values between species were low (< 0.4) for 80% of the pairs in each season, suggesting wide partitioning of the food resource. The fish assemblage showed a tendency toward trophic specialization, regardless of the season, although several species changed their diets. We might consider two non-excludent hypothesis: that there is no pattern on the use of seasonal food resources and/or probably there are several patterns, because each one is based on characteristics of the studied site and the taxonomic composition of the resident species.
Highlights
Studies of feeding in fish assemblages in a particular site allows us to recognize distinctive trophic guilds, and make inferences about their structure, the degree of importance of the different trophic levels and the relationships among their components
Stomach content analysis showed that 24 food items were consumed by the fish fauna
Plants occurred in the diet of nine and ten species in the rainy and dry seasons respectively, but were the preferred food of 11% of the fish species in the rainy season (Tables 2 and 3)
Summary
Studies of feeding in fish assemblages in a particular site allows us to recognize distinctive trophic guilds, and make inferences about their structure, the degree of importance of the different trophic levels and the relationships among their components. In regard to trophic relationships among Neotropical fishes, one of the major challenges is to understand the ecological mechanisms by which a large number of species are able to coexist in the same community and the manner in which resources are shared (Esteves & Galetti, 1994). Neotropical freshwater ecosystems undergo cyclic changes in response to alternating wet and dry seasons. These changes affect the food resources for the fish fauna, and according to several researchers (Araújo-Lima et al, 1995; Winemiller & Jepsen, 1998; Lowe-McConnell, 1999; Yamamoto, 2004; Hahn et al, 2004) may modify the trophic spectrum and the feeding rhythm of the fish, influencing the trophic relationships among species. These changes affect the food resources for the fish fauna, and according to several researchers (Araújo-Lima et al, 1995; Winemiller & Jepsen, 1998; Lowe-McConnell, 1999; Yamamoto, 2004; Hahn et al, 2004) may modify the trophic spectrum and the feeding rhythm of the fish, influencing the trophic relationships among species. Esteves & Aranha (1999) noted that studies of the effects of hydrological changes on fish assemblages may elucidate qualitative and quantitative changes in the diet for different species resident in the site
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