Abstract Poecilia reticulata is a type of small ornamental fish that lives in the dam located in the Riau University campus. This study aims to understand the reproductive biology aspects of that fish, especially sex ratio, gonadal developmental, fecundity, and egg diameter. The fish was sampled 2 times/week from March to May 2019. Total fish captured was 71 (44 males and 27 females). The …