Composição e Abundância do Ictioplâncton na Confluência dos Rios Madeira e Amazonas.

Abstract

The loss of diversity is one of the main damage to the environment caused by the construction of the reservoirs and it is related to the disappearance of terrestrial habitats by flooding, and the changes produced in the aquatic habitat. These changes reflect, above all, in the availability of food and in the reproduction of the fish species, leading to a remarkable structural change on aquatic communities in relation to the originals. This study aimed to estimate the richness and characterize the composition of the ichthyoplankton on the Madeira River and the Amazonas River. Monthly collections were conducted from November 2009 to February 2010, it is using net of ichthyoplankton of the conical type of mesh 350 μm with fluxgate connected to the mouth and a deflator type sled to stabilize it and lad it to the bottom, the samples were preserved in formol 10%. Simultaneously, water samples were collected for the obtaining of the temperature, dissolved oxygen, pH, electric conductivity and turbidity. The abundance of fish eggs and larvae was standardized for 50m3. In the laboratory samples were screened and larvae identified to lowest possible taxonomic level and separated but the degree of flexion of notochord. There were collected 180 samples resulting in the capture of 464 eggs and 165.207 larvae. It was found that among the environmental variables analyzed the pH and electric conductivity were highest in the river Amazonas while the turbidity was highest in the river Madeira. The largest densities of eggs and larvae happened in the month of January for the rivers Amazonas and Madeira and, in the month of February for the river Amazonas downstream. Larvae were found of sixteen families, most abundant families were Hemiodontidae (44,2%) for the river Amazonas, Characidae (34,2%) for the river Madeira and Curimatidae (29,7%) for the river Amazonas downstream. During the period of studies individuals of all the stages were present, but the stages of preflexion and yolk-larval showed values highest. The taxonomic composition was similar among the sites studied. For the river Amazonas and river Madeira similarity was lower (0,635) than between the river Madeira and river Amazonas downstream (0,755). The river Madeira, largest tributary of the river Amazonas, is used as reproduction site by several fish species of the Amazonica region, thus the maintenance of their integrity is important for the preservation of diversity and enhancement of fishery.