Spatial and temporal variation in population structure of Hemigrammus marginatus (Characiformes: Characidae) in streams of the Ivinhema River Basin, Brazil
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The present study has assessed spatial and temporal variations in the length structure of Hemigrammus marginatus Ellis, 1911 and estimated growth parameters for the species. Sampling was carried out in five streams in the Vitória and Piravevê sub-basins of the Ivinhema River from January to December 2002. A total of 933 specimens of H. marginatus were caught (97 in the Vitória sub-basin and 836 in the Piravevê sub-basin). Mean length of the individuals caught in the Piravevê sub-basin was shorter (21.58 mm, SD = 4.67) than that of individuals caught in the Vitória sub-basin (29.24 mm, SD = 4.42). Analysis of condition factor calculated from the weight/length relationship revealed that the values were constant both spatially (between sub-basins) and temporally (throughout the year). In the Piravevê sub-basin, the theoretical maximal length estimated for this species was 37.26 mm, with natural mortality rate of 1.22 year¹, growth rate (k) of 0.66 year-1, and growth performance index (w) of 3.80 and 4.25 years of longevity. The input of new individuals in the population occurs twice per year, with greater recruitment at the peak of the rainy season (May) and the peak of the dry season (August).