This study aimed to analyze the distribution of size classes and sex ratio to broaden the knowledge on the reproductive behavior of Diplodon expansus (Küster, 1856) and the biodiversity of the water bodies of the Área de Proteção Ambiental Piraquara, Paraná, Brazil. The study area is a section of the Piraquara river, characterized by lotic water and relatively well preserved riparian vegetation. Four samplings were carried out from March 2006 to December 2006. In the Piraquara river, D. expansus occurs in sections of the river with sandy and slimy substrate. The length of specimens ranged from 17 mm to 65 mm, and the highest frequencies of length classes were found for intermediate sizes. Histological analysis of gonads revealed a 1:1 sex ratio. No hermaphrodite specimens were found, characterizing a dioecious population. Qualitative and quantitative analysis showed a continuous gametogenesis, with peaks of larval release in the summer.
Unionoida; reproduction; gametogenesis; histology
