Fator de condição de peixes do sistema do Lago Grande, Manacapuru, Amazonas

Abstract

Marked by a well defined alternation between the terrestrial and aquatic stages, the Amazon floodplain has a low climatic seasonality, with daily oscillations on temperature higher than annual and less pronounced variation of the photoperiod throughout the year. These environments are also characterized by the standard uni-modal and predictable flood with large seasonal variation in water level. For the fish fauna of the floodplain, the direct effects of changes in water level include severe changes in community composition and density of the population, conditioned by changes in limnological characteristics and the availability of food. Such seasonal variations in terms of feeding and reproductive responses may be expressed by the condition factor, quantitative indicator of the wellfare in front of the fish conditions of their environment. This study aimed to provide information on the seasonal variation of fish species condition factor in the Jaitêua and São Lourenço lakes that composes the Lago Grande System in the city of Manacapuru, Amazonas State. Data collect were made monthly for the period from July 2006 to July 2007. Once the condition factor were calculated, the comparisons between periods were performed by ANOVA. The comparisons between sexes and between juveniles and adults were made by t test. PCA was used to identify groups of species whose pattern of variation of the condition factor is similar. After critical data analysis, there were selected 13 species to study. The seasonal variation of the condition factor was significant for Acestrorhynchus falcirostris, Triportheus albus, Triportheus auritus, Potamorhina altamazonica, Potamorhina latior, Pygocentrus nattereri, Serrassalmus altispinis, Pellona flavipinnis and Hypophthalmus marginatus. Only Schizodon fasciatus, Serrassalmus spilopleura, Plagioscion squamosissimus and Hoplosternum littorale showed no seasonal variation in the condition factor. Despite the influence of reproductive characteristics, we can point at feeding habits as a biological trait that best explained the seasonal variation of the condition factor of fish species in the study area. Based on the local history, the hydrological cycle was considered atypical during the study period. Also, it was observed differences between cycles in the lake and in the main river. For most of the selected species, male and female seasonal variation in the condition factor showed similarities. Comparing juveniles and adults, the variation patterns of the two groups were different for the vast majority of species.