This study investigates the population structure and the reproductive biology of Parastacus defossus Faxon, 1898, a fossorial species that spends its life inside subterranean tunnels. Around 30 specimens were collected each month in the region of Lami, municipality of Porto Alegre, state of Rio Grande do Sul, Brazil, from January, 2003 to August, 2005. The minimum, the maximum, and the mean carapace length of males, females, juveniles and individuals with ootestis were recorded. The frequency distribution by size classes, the sexual proportion, the recruitment, and the reproductive period were analyzed. A total of 766 specimens were collected, from which 315 were males (41.12%), 278 were females (36.30%), 166 were juveniles (21.67%), and seven individuals had ootestis (0.91%). Males and females were present in all months and in all size classes. The highest frequency of individuals matched the size classes from 24 to 30 mm. The highest frequency of juveniles was recorded during the spring of 2003 and the summer 2005. Significant differences in the size of males and females were recorded in the size classes between 26 and 30 mm. The sex ratio between all males and females was 1:0.88 (x² = 2.3, p > 0.05). The proportion between males and females showed significant differences between the size classes 26-28 mm (x² = 5.43, p < 0.05) and 28-30 mm (x² = 4.77, p < 0.05) carapace length, were the number of males was highest. Of the 278 females, only 17 were ovigerous (6.11%) and the reproductive period was clearly restricted to the spring.
Crayfish; recruitment; reproductive period; sex ratio
