Investigating the life history of Pyrrhulina capim (Characiformes: Lebiasinidae) in eastern Amazonian streams

Abstract This study described the life history of Pyrrhulina capim in streams of the Eastern Amazon, linking key environmental predictors that can influence its reproductive activity. Specimens were collected between March 2019 and March 2020 in a stream of the Guamá River basin. The P. capim population was assessed for sex ratio, length at first maturation (L50), gonadal maturation activity, growth pattern, spawning type, and fecundity. The effects of environmental variables on reproductive activity were analyzed separately by sex using Multiple Linear Regression (MLR). A total of 404 individuals were analyzed, comprising 218 females and 186 males, with no significant bias in sex ratio. Females reached first maturation at 24.91 mm, whereas males reached it at 21.47 mm. The reproductive activity was consistent in both sexes throughout the study period. The species exhibited positive allometric growth (b = 3.12) with no notable differences between males and females. Oocyte diameters ranged from 0.05 mm to 0.70 mm, indicating multiple-batch spawning. Average fecundity was 162 eggs. Stream width, depth, and substrate type accounted for 13% of the variability in female reproductive activity. These findings suggest that P. capim adopts an opportunistic reproductive strategy.