BIOLOGIA POPULACIONAL DE Macrobrachium jelskii (MIERS, 1778) (CRUSTACEA, DECAPODA, PALAEMONIDAE) EM UMA PLANÍCIE INUNDÁVEL NA AMAZÔNIA ORIENTAL, BRASIL.

The population biology of M. jelskii was investigated with emphasis on the length frequency distribution, sex ratio, breeding season and length and weight ratio. Sampling was conducted during the April/2008 May/2009 along with macrophytes in a transect of 50 m. The samples were obtained using sieves of 55 cm diameter and a 2 mm mesh, on a 2 m space interval, totaling 25 samples throughout the study period. In the laboratory, specimens of M. jelskii were measured, weighed, sexed and females classified macroscopically as to the degree of maturation. There were found 910 specimens, 505 males and 405 females. The total length ranged from 9.7 to50.3 mm, and a higher frequency of subjects on the classes occurred between 19.7 to21.7 mm and from 37.7 to39.7 mm. The males showed greater sizes and sex ratio was stable between months. Reproduction occurred in the rainy season. Females had isometric growth and male allometric negative, showing dimorphism in relations total weight/total length of both sexes. Keywords: floodplain area; ressaca area; shrimp.