Abstract
The reproductive biology of Poecilia latipinna inhabiting Wadi Haneefah stream, Riyadh, Saudi Arabia was studied. The fish (P. latipinna) were found reproductively active round the year. The highest reproductive activity occurred from February to May and August to November which defined two distinct annual periods of reproduction. There was a monthly variation in sex ratio. More females than males were registered during the whole. period of study. Males mature at the total body length of 51 mm, while the female maturity was attained at 48 mm. Fifty percent male and female population achieved maturity at the length of 67 mm and 65 mm body length, respectively. The absolute fecundity of P. latipinna ranged from 35 to 161 eggs, the value of co-relation coefficient (r) indicates that the fish's fecundity has stronger relation with weight than with the length.