Influência da heterogeneidade do substrato e da profundidade sobre as categorias tróficas de peixes de igarapés na Amazônia

Abstract

Variations in the type of submerged substrate and the depth of the channel are physical characteristic of the streams environments that play an important role in determining the trophic structure of the fish. However, that relation in tropical streams and Amazonian streams doesn’t know. In this sense, ecological aspectsrelated to trophic structure of fish communities in upland streamswere studied, especially those related to the influence that the heterogeneity of substrate and depth have on the composition of trophic categories of the fishes. The trophic structure of 59 streams of 1st and 2nd order in different areas of the Brazilian Amazon were studied, which resulted in the trophic classification of 172 species of fish. There was no correlation between the diversity of trophic categories of fish and diversity of substrates or channel depth on the areas sampling. However, the relative biomass of fish in the samples showed positive feedback with the diversity of substrates, but not with the depth. Analysis of stomach contents of fish revealed that items autochthonous origin have greater importance; most species studied were classified as autochthonous insectivorous. It is possible that the lack of relationship between the substrate heterogeneity and diversity of trophic categories result from the fact that the system of fish species occupy almost the entire small water column, show the generalized diet and foraging strategy opportunistic, consuming both autochthonous as allochthonous items explaining, therefore, the lack of relationship between the diversity of substrates and trophic categories.Thus, the different types of substrate are used for both shelter and foraging, explaining the lack of correlation. The depth of the environment didn’t influence the diversity of trophic categories, once headwater streams have smaller dimensions and well closed canopy, which impede the entry of light and, consequently, the presence of larger individuals.The lack of correlation of relative fish biomass with depth can be explained by the physical limitation to the use of space (represented by channel lower depth), that seems to be an important factor which impede the occupation of small streams by a greater diversity of species.On the other hand, the relationship observed between the relative fish biomass and diversity of substrates may be the result of energy resources derived from autotrophic processes, which seem to supply a large quantity of individuals and/or total weight of fish, which makes these organisms depend on food resources of autochthonous origin.