Ethiopia has a rich diversity of ichthyofauna in its lakes, rivers and reservoirs. This study was conducted to identify fish species composition, estimate relative abundance, and assess length-weight relationship and condition factor for the dominant fish species in Gilo River and its nearby wetlands in Akobo district, Gambella Region, Ethiopia. Baro River in Gambella region is documented as the most diverse in fish species. Besides this, its nearby wetlands, tributaries and lakes which are expected to have rich fish species are least explored for their fish diversity. Samples were collected from selected sites using gill nets of various mesh sizes and hooks and lines. Fish sampling was done twice in dry season (December, 2016 and March, 2017) and twice in wet season (May and June, 2017). A total of 911 specimens were collected. These were identified into 27 species, 21 genera, 17 families and five orders. The Shannon diversity index (2.28) of fish species was higher in river than in wetlands (1.85); the same is true for the index of evenness for river (0.69) was also higher than the wetlands (0.67). The length-weight relationship of most of the species evaluated demonstrated positive allometric growth. Seasonal variations in the mean FCF of the most dominant species were statistically insignificant (p>0.05) except for Clarias gariepinus and Citharinus citharus. All the species identified in this study are new report to Gilo River and its nearby wetlands representing a baseline data for the study area. Anthropogenic activities i.e. fishing, farming, construction and other domestic activities were observed in the study sites. Plausible management options have to be encouraged to ensure sustainable utilization of the fisheries resources of the study area.