Since 1970s riverine fishes have continuously declined and this has been attributed to anthropogenic factors. Continuous monitoring of riverine fish communities is therefore a requirement. Knowledge on biology of the existing fish species provides a basis for appropriate intervention strategies. This study is aimed at determining the spatial variation in fecundity, gonadal maturity stages of Labeobarbus altianalis along River Nyando. Sampling was done monthly for six months from Dec 2014 to May 2015. Three sites S1 at the upper region; S2 at the mid region and S3 at the lower region closer to the river mouth were sampled. Fish sampling was done using an electro fisher and the sampled fish identified in the field. The length and weight of Barbus altianalis were taken in the field to the nearest 0.1 g. Fresh ovaries were fixed in buffered 10% formalin for 12 hours and stored in 70% ethanol for determination of fecundity within the three sampling sites. At all the sampling sites females were significantly higher than males (Chi-square test; P < 0.05). Highest fecundity occurred in fish sampled from S1 49,440 ± 11,432 eggs/L) this could be attributed to the high proportion of females at the ripe/running stage followed by fish sampled from S3 (37,453 ± 7895 eggs/L) while the least fecundity occurred at site S2(32450 ± 4235 eggs/L). Gonado somatic indices remained clearly high mostly above 2 for females in all the three stations. Where there were low proportion of ripe/running females At all the sampling sites females were significantly higher than males there could be a possibility of sex reversal where males reverse their sex in response to environment another factor could be male mortality due to greater reproductive investment.
