ABSTRACT Inland fisheries are particularly important for the food security of poor people, as most inland fish production goes for subsistence or local consumption.The main objective of this study was to assess some biological aspects and post-harvest loss of fish in upper Dabus River. The study was carried out from September, 2017 up to July, 2018. Gillnets of stretched mesh size 6, 8, 10, 12 and 14 cm monofilaments, and hookswere used to catch fishes.Physico-chemical parameters of water such astemperature, transparency, conductivity, pH and total dissolved solid of the river were takenusing multi-meter. An index of relative importance (IRI) and Shannon diversity index (H') were used to evaluate relative abundance and species diversity of fishes, respectively. A total of 565 individual fishes belonging to 3 orders, 3 families (Clariidae, Cichlidae and Cyprinidae), 3 genera and 3 species were identified in Dabus River. Out of the total catch of specimens the dominant fish species Clarias gariepinus contributed 65.8% of the catch. Among sampling sites diversity index was highest at Musa Dabus sample site than the other sites. C. gareipinus was the most abundant species according to IRI (78.05%), while Labeobarbus intermedius was second (16.5%) and Oreochromis niloticus (5.5%) was third in total catch. The monthly gonad-somatic indicated that the spawning season for C.gariepinus species was from May to June. The length-weight relationship of Dabus fishes were curvilinear and the relation was statistically significant (P<0.001).The mean Fulton Condition factor of C.gariepinus and L. intermediusshowed significant difference (P<0.05) between sexes. For the three fish species, the sex ratio did not vary from unity. The relationships between absolute fecundity with total length, total weight and gonad weight of C. gariepinus were linear and significant (P<0.05).Absolute fecundity of C.gariepinus at Dabus River ranged from 54409 to 258551with a mean of 84009 eggs. The post-harvest fish losses appraised in study area were physical loss ofpredation and spoilage with estimated values of 5.81kg(1.97%) and 13.2 kg (4.5%), respectively. In order to have a better understanding of the fish populations in the study area, further studies with more sampling sites and months are required on biologyand post-harvest loss of the fishes. Keywords:Conditionfactor,Dabus river,length-weight,post-harvestloss,Reproductive biology