Fontes autotróficas de energia de peixes de importância comercial do Lago Grande, Manacapuru-Am, Brasil

Abstract

The lowland areas of the Amazon region have an abundant and diverse ichthyofauna, supporting the activity of major importance in the region, fishing. These areas suffer from seasonal variations in water levels, so that there is a change in the availability and diversity of food in periods of high and low water for the species. This study investigated autotrophic energy sources commercially important fish of the Grande Lake. Samples of fish and autotrophic energy sources were collected during periods of drought and flood season with the Grande Lake, Manacapuru, Amazonas, Brazil. We determined the isotopic composition of C and N of the dorsal muscle of fish and autotrophic sources (phytoplankton/seston, macrophytes C3 and C4 and plants the flooded forest). To calculate the estimates of the contributions of autotrophic energy sources, we used the mixture model with multiple sources through the computer program Isosource. During the dry season samples were collected phytoplankton/seston, macrophyte C3 and macrophyte C4 with average values of 13C and 15N of -34.9‰ (  0.6) and 5.9‰ (  0.5), -29.3‰ (  1.6) and 7.1‰ (  1.5) and -12.7‰ (  0.4) and 8.4‰ (  1.3), respectively. In flood period samples were collected phytoplankton/seston, macrophytes C3, macrophyte C4 and plants of the flooded forest with average values of 13C and 15N and -31.8‰ (  0.3) and 6.1‰ (  0.2), -29.3‰ (  1.5) and 3.6‰ (  1.6), -11.3‰ (  0.1) and 6.6‰ (  2.9) and -29.1‰ (  1.5) e 3.3‰ (  1.9), respectively. The fish species during dry periods and had a full range of variation of 13C of - 27.4 ‰ – -34.7 ‰ and 15N of 2.5 ‰ – 11.9 ‰. For the calculations of estimates of the contributions of autotrophic sources was necessary to combine the sources macrophytes C3 and plants of the flooded forest, as these had isotopic values similar carbon and nitrogen, from this group to be defined as macrophytes C3/plants of the flooded forest. Estimates of the contribution of autotrophic sources during the dry season showed that O. bicirrhosum, P. nigricans, Astronotus sp. and C. macropomum have greater contribution as source of phytoplankton/seston, with contribution values of 54.6%, 98.3%, 70.4% and 94.7%, respectively. The only species that showed macrophytes C3 during the dry season as source of greatest contribution was to P. brachypomus of 48.4%. Astronotus sp. continued with the phytoplankton/seston as source of greater contribution (84.0%), while C. macropomum and P. brachypomus present macrophytes C3/plants of the flooded forest with 48% and 82.5%, respectively. The species C. monoculus, M. duriventre, P. squamosissimus, P. nattereri presented as autotrophic source energy of during periods of study of the macrophytes C3/plants of the flooded forest as source of major contribution, with values of 64.6%, 96%, 50% and 80.5%, respectively. The species H. malabaricus during the study periods presented phytoplankton/seston as source of greater contribution to the species (46.1%). The investigation of autotrophic energy sources for the species showed that O. bicirrhosum and P. nigricans phytoplankton/seston was the source of greatest importance for the species in the dry season. The species C. monoculus, M. duriventre, P. squamosissimus and P. nattereri not changed its autotrophic energy source of during periods of study presented as source of greater importance to the biomass of the macrophytes C3/plants of the flooded forest. The species Astronotus sp. and H. malabaricus also have not changed their autotrophic energy source during periods of study by presenting the phytoplankton/seston as source of greater importance. Among the species studied only the species C. macropomum and P. brachypomus changed its autotrophic source energy. In the period of high waters had the macrophytes C3/plants of the flooded forest. During the dry season C. macropomum phytoplankton/seston and P. brachypomus the macrophytes C3 as source of greater importance.