Population biology of the freshwater prawn Macrobrachium brasiliense (Heller, 1862) in the Middle Amazon Region, Brazil

The population structure and reproduction of Macrobrachium brasiliense were studied with the aim of better understanding the ecology of this species in relation to the Amazonian flood-pulse regime. A total of 3,306 animals were caught monthly from August 2011 to July 2013 at the Carú River, Itacoatiara, Amazonas State (Brazil). The average carapace length of males (6.87 ± 3.45 mm) and females (6.88 ± 4.78 mm) did not differ significantly (U = 0.608; p= 0.5432) for the overall study period. The sex ratio was biased toward females (M:F = 1:1.61; χ2=83.855; p< 0.0001). The reproduction was continuous, and although juveniles were present throughout the study period, the recruitment occurred primarily during the ebb (August–September) and drought (October–December) periods. Macrobrachium brasiliense presents a low number of large eggs, and egg volume increased during embryogenesis, by 21.1% from Stage I to III. The population size-frequency distribution presented no correlation with the abiotic variables, but its reproductive period seems to be related to the Amazonian flood-pulse regime.