The length-weight relationship, condition factor, feeding and reproduction of O. lIiloticus from Lake Chamo,rnEthiopia were studied from March 1996 to March 1997. The length-weight relationship of 1473 fish ranging in sizernfrom 125 to 610 nun Total Length (TL) and in weight from 42.5 to 4800 g Total Weight (TW) was computed. Thernrelationship between total length and total weight for the total sample was curvilinear, and described by: TW =rn0.0258TL'Â·"'. The regression equation for the females was TW = 0.069TL'Â·63 and for the males it was TW =rn0.022TL'Â·99. Fulton's and relative condition factor was calculated for both sexes separately. There was arnsignificant variation in the mean monthiy condition factor of both sexes (ANOY A, P < 0.05). The mean Â± SErnFulton's condition factor of O. ni/oticus in Lake Chamo ranged from 2.10 Â± 0.03 to 2.35 Â± 0.10 for the males,rnfrom 1.96 Â± 0.03 to 2.1 Â± 0.04 for the females. The food of O. niloticus in Lake Chamo was studied from thernstomach contents of 449 fish measuring 290-570 mm TL. In addition, a total of 145 juvenile O. ni/oticus, rangingrnfrom 61 to 115 mm caught during three sampling occasions were also examined for diet composition analysis. Therndiet of adult fish consists of 10 genera of blue greens, 8 genera of green algae and more than 8 genera of diatoms.rnBlue greens as a group contributed the bulk of the diet. The most frequently encountered species from the bluerngreens were Allabaena (96-100), Microcystis (82-100) and Oscil/atoria (41-100). In terms of percentagerncomposition by number, the blue greens contributed over 60% of the total food ingested. Of these, more than 50%rnwas contributed by Anabaena, Microcystis and Oscillatoria. When the food items were expressed as percentagernvolume, the blue greens made up 32.2% whereas the green algae and the diatoms contributed about 32.3 andrn35.2%, respectively. The mean percentage dry weight of the green algae, diatoms and blue greens was 53.8, 28.2rnand 17.7%, respectively. Among the green algae, Cosmariu/ll alone contributed more than 40% to the total dryrnweight. Zooplankters occurred on rare occasions in the stomach contents of adult O. niloticus -w-he-re'a-s -th-es.e. ' -w-"e rernrelatively more frequent (1.8%) in the diet of the juveniles. The feeding pattern of O. niloticus was observed torn- - - -. - .-. -". ,- . --. - - _ ... -_.'-" -- .. -_. -... - ."--- --- - -, -, .---_._,,-. - -- - --.-. --------------rnhave a diel rhythm. O. lIi/oticus in Lake Chamo is a continuous feeder during the day. Daily ingestion ofrnphytoplankton was estimated to be about 3.75% of its body weight per day at an average water temperature of 26 'rnC. Gonads from a total of 1349 O. niloticus were examined in this study. The mean monthly gonado-somatic indexrn(GSI) of the males ranged from 0.21 to 0.51 whereas that of females ranged from 0.51 to 1.56. Higher values forrnthe females were observed between March and June, and for the males between March and May, 1996. The patternrnof gonad development for both sexes was more or less similar. Ripe males occurred at high frequenciesrn(ranged:39-60%) in March, April and May, 1996. The percentage of ripe females ranged from 47 to 53 withrnseasonally highest frequencies occurring from March to June, 1996. Thus, it was concluded that O. ni/oticus inrnLake Chamo spawns throughout the year with peak breeding activity in March, April, May and June. The smallestrnsexually mature female was 385 mm TL, whereas the male was 395 mm TL. However, the 50% maturity lengthrnwas415 mm TL for females while 425 mm TL for males. O. ni/oticlls were all mature above 500 mm TL. Thernaverage fecundity of O. niloticus ranging in Length from 390 to 560 mm TL, and in weight from 1300 to 3900 grnwas 2493 Â± 300 (N =209). The smallest count was 1047 (fish length=470 mm TL) whereas the largest was 4590rn(fish lengtll=510 mrnTL). In general, fecundity of O. lIiloticus in Lake Chamo was linearly related to total length,rntotal weight and gonad weight.