Pantanal is known because of the amplitude on the water dynamics, with a pronounced flood and dry seasons. The water expansion and retraction reflect in the hydric connectivity between river and bays, resembling the environments and causing distinct characteristics of water quality. In order to capture fish in these environments the gill nets are used. These passive devices allow the capture of a certain length category according to the meshes size, avoiding the capture of fish that are too small or too large, characterizing their selectivity. The present study aims to characterize the ichthyofauna of an oxbow lake system, as well as to establish its relationship with the seasonal, limnology and structural alterations of fish, seeking to understand the spatial and temporal distribution characteristics of the community. Three points of two side lakes were sampled using a set of gill nets with 2, 3, 4 and 5 cm between knots, allocated in parallel columns at every 10 meters in the lakes. The samples were performed during the day and during the night, where the nets were left in the water for 6 hours. Concomitantly to the fish sampling, the limnologic variables were obtained using a portable field equipment and Secchi disk. The results showed that the limnological variables changes according to the hydric seasons. These changes associated to the connectivity between the river and lakes presented an increase in the diversity indices considering the inlet of water in the system, while the disconnected lakes remained about the same during the entire year. This discrepancy may be caused by the selectivity of the gill nets using in the study, where fish may use the flooded area during the high waters, reducing the capture capacity of these devices. In the Pantanal, the connectivity associated to the selectivity of the gill nets determine the fish community.
