Life history traits of Characidium pterostictum (Characiformes, Crenuchidae) along the longitudinal gradient of a Neotropical river in southern Brazil

Life history traits of Characidium pterostictum Gomes, 1947 (Characiformes, Crenuchidae) from three different reaches of the upper Sinos river, southern Brazil, were described and comparatively analyzed according to the longitudinal gradient. For all reaches, results indicated a seasonal reproductive strategy with a higher intensity during warmer months of higher photoperiod (November to February). Only females were found in the upstream reach and they were more numerous than males in all the sampled reaches. Mean absolute fecundity ranged from 5,189 (+/- 2,131 SD) to 7,394 (+/- 3,807 SD), whereas mean relative fecundity (oocytes per mg of female total weight) ranged from 1.08 (+/- 0.40 SD) to 1.12 (+/- 0.29 SD). Oocyte development was characterized as synchronic in two groups, typical of total spawning. Longitudinal gradient comparison suggests that body size (standard length) of C. pterostictum individuals and sex ratio were the only characteristics that differed between sampled reaches. Larger individuals and thus females tended to be more frequently found in upstream reaches of the Sinos river, with a decrease in body size and in the proportional number of females towards downstream.