Freshwater mussels of Catalão , confluence of Solimões and Negro rivers , state of Amazonas , Brazil

The present study provides a species list of freshwater mussels from Catalão, the meeting of the Solimões and Negro rivers, in state of Amazonas, northern Brazil. Expeditions to collect molluscs were carried out between 2004 and 2006, during high and low water seasons. Three hundred and thirty-one bivalve shells, 25 valves, and 57 live specimens of four families and 10 species were identified. A single exotic species, Corbicula fluminea, represented over half the collected shells. All bivalve shells were photographed and registered at the mollusc collection of the Instituto Nacional de Pesquisas da Amazônia (INPA), Manaus. Introduction Documentation of the Catalão aquatic fauna has been carried out for some taxa. Anjos et al. (2008), collected 103 species of fishes. Freshwater mussels have not been cited for this region, probably due to the difficult access to these animals during most of the year. Mansur and Valer (1992), studying bivalves from the Branco and Uraricoera rivers in state of Roraima, and Pimpão (2007), studying mollusc species from the Madeira and Aripuanã rivers, in state of Amazonas, both mention the total absence of freshwater mussels during the high level water season (with the exception of some Sphaeriidae). Bivalves, usually buried and distant up to 15 m from the water surface, are inaccessible by manual sampling in high water season. Species lists of Brazilian freshwater molluscs from the Amazon are rare despite of their high diversity (Simone 2006). This makes their identification difficult for non-specialist researchers and there may be more species yet to be described from the region. For example, Mansur and Pimpão (2008) described a new freshwater mussel from the Amazon basin, based on shell characters. We present herein the first illustrated list of freshwater bivalves from Catalão, in state of Amazonas to help nonmalacologists and local students to identify them and to contribute to knowledge of this poorly studied fauna. Figure 1. Map showing the location of Catalão and the four sampling points, municipality of Iranduba, state of Amazonas, Brazil. A. Exposed benthos near Catalão lake. B. Right bank of Negro river; C. Margins of Xiborena and Pirapora channels; D. Catalão lake, floating substrates. Modified from Ministério do Exército, Depto. de Engenharia e Comunicação, 1997, Folha AS.21-Y-CI MI-579.


Introduction
Documentation of the Catalão aquatic fauna has been carried out for some taxa.Anjos et al. (2008), collected 103 species of fishes.Freshwater mussels have not been cited for this region, probably due to the difficult access to these animals during most of the year.Mansur and Valer (1992), studying bivalves from the Branco and Uraricoera rivers in state of Roraima, and Pimpão (2007), studying mollusc species from the Madeira and Aripuanã rivers, in state of Amazonas, both mention the total absence of freshwater mussels during the high level water season (with the exception of some Sphaeriidae).Bivalves, usually buried and distant up to 15 m from the water surface, are inaccessible by manual sampling in high water season.
Species lists of Brazilian freshwater molluscs from the Amazon are rare despite of their high diversity (Simone 2006).This makes their identification difficult for non-specialist researchers and there may be more species yet to be described from the region.For example, Mansur and Pimpão (2008) described a new freshwater mussel from the Amazon basin, based on shell characters.We present herein the first illustrated list of freshwater bivalves from Catalão, in state of Amazonas to help nonmalacologists and local students to identify them and to contribute to knowledge of this poorly studied fauna.

Material and methods
The Catalão area is located at the confluence of Solimões and Negro rivers (Figure 1), in the municipality of Iranduba, near Manaus, state of Amazonas, Brazil.This region is flooded annually by Solimões and Negro waters between April and August.According to Anjos et al. (2008) the area is influenced mainly by the white waters of Solimões river, which has a neutral pH, high electric conductivity and is loaded with suspended solids.The low water period occurs in October and November, when most of the freshwater mussels and/or their shells can be observed.
Field surveys were carried out at high and low water seasons between 2004 and 2006.The bivalves were collected manually from four sites: 1) exposed benthos near the water at Catalão lake; 2) the right bank of Negro river; 3) banks of Xiborena and Pirapora channels; 4) on floating tree trunks and Eichhornia spp.from Catalão lake.Live specimens were preserved in 70% alcohol and empty shells were washed and dried.All material was registered at the mollusc collection of the Instituto Nacional de Pesquisas da Amazônia, in Manaus.The description of shape of shells followed Mansur and Pereira (2006)

Results and discussion
A total of 331 bivalve shells, 25 valves and 57 live specimens belonging to four families and 10 species (Table 1) were recorded for the Catalão region.Mansur and Valer (1992) registered three families and 10 bivalve species from the Branco and Uraricoera rivers, state of Roraima, northern Brazilian Amazon.Pimpão (2007), recorded 13 taxa of freshwater mussels from the Aripuanã river, a tributary of the Madeira river.The species richness of each family in the Catalão survey was: Mycetopodidae (five species), Hyriidae (three species), Sphaeriidae and Corbiculidae (one species each).One of the species collected in the Catalão area was Corbicula fluminea, an exotic species, which represented more than half of the collected bivalve shells.
All freshwater mussels, with the exception of Eupera simoni (Figure 10), were collected during the dry season, when live specimens and empty shells were more accessible.However, as E. simoni can be found in floating substrates such as dead tree trunks and Eichhornia spp., this was the only species collected during high water.Future surveys in Catalão with objectives to sample a largest number of freshwater bivalves species must include low water season.It is due to the great variation of the water level in the rainy season and difficulties of using benthos samplers to reach bivalves on the bottom.The presence of trees and roots prevents the use of trawl nets and the low visibility and great depth do not allow a secure diving.

Figure 1 .
Figure 1.Map showing the location of Catalão and the four sampling points, municipality of Iranduba, state of Amazonas, Brazil. A. Exposed benthos near Catalão lake.B. Right bank of Negro river; C. Margins of Xiborena and Pirapora channels; D. Catalão lake, floating substrates.Modified from Ministério do Exército, Depto.de Engenharia e Comunicação, 1997, Folha AS.21-Y-CI MI-579.