Macrobrachium jelskii is popularly knowledge in Brazil as the “sossego” shrimp. This work was conducted in the Três Marias Reservoir (18°21'49" S and 45°19'55" W) and in the São Francisco River (18°12'30" S and 45°15'50" W) from March/2005 to February/2006. The objective of this work was to study the Macrobrachium jelskii population biology. A total of 2.945 shrimps were collected, 1.064 individuals (36.13%) were males, 1.857 (63%) were females and 24 (0.81%) were juveniles in the Reservoir and a total of 1.973 shrimps were collected in the River, where 1.120 individuals (56.76%) were males, 841 (42.62%) were females and 12 (0.61%) were juveniles. Total length varied from 5.07 t o 51.21 mm and from 11.3 to 50.34 mm in the Reservoir and in the River, respectively, and the females were the largest individuals in both places. The sex ratio was 0.57 in the Reservoir and 1.33 in the River. The juvenile recruitment in the Reservoir occurred in January, while in the River occurred in December. The reproductive period occurred during whole year with high intensity in January in the Reservoir and, November and December in the São Francisco River. The ovigerous female showed a total length from 30.32 to 50.64 mm and from 35.24 to 48.72 mm in the Reservoir and in the River. The onset females’ maturity was observed at 30.32 mm of total length in the Reservoir and 35.24 mm in the River. The mean fecundity was 37 ± 14 eggs to animals in the Dam and 35 ± 14 eggs in the River. The Reservoir’s shrimp showed 1.54 ± 0.07 and 2.07 ± 0.12 mm for the minor and major axis of the eggs, respectively, during the initial stage of embryonic development. And the River’ shrimp showed 1.59 ± 0.06 and 2.17 ± 0.11 mm for the minor and major axis of the eggs, respectively. The male’s relationship weight/cephalotorax length showed a larger increase in the cephalotorax length in the Reservoir and in the River in the rainy-hot and dry-cold station. The females have a larger increase of the weight in the rainy-hot station in both places. The males obtained a larger value of the condition factor in the Reservoir and in the River, in comparison with the females. The females in the Reservoir and in the River have larger condition factor in the dry-cold station. In the study of the relative growth the relationships CC/AAb (cephalotorax length/ abdomen height) and CT/AAb (total length/abdomen height) showed the best relationships for comparison between males and females. Key words: Growth, Population structure, Reproduction. |