Reproductive biology is important in the life of organisms, because through it, ripe and fecund females produces their young. Macrobrachium vollenhovenii is one of the species of Macrobrachium found in fresh and brackish waters of West Africa. It is one of the largest species of Macrobrachium known which makes it a suitable choice for aquaculture in Nigeria. The sex ratio, fecundity, egg diameter and the gonado-somatic index of M. vollenhovenii from Badagry, Lagos and Epe Lagoons, Nigeria were investigated. The samples were collected monthly from the lagoons for 24 months between June, 2013 and May, 2015. The sex ratio showed that there was significant difference (P < 0.05) in the result recorded in the three lagoons with more males in Badagry and Epe while Lagos Lagoon had more of females. The fecundity estimates of M. vollenhovenii from the three lagoons ranged from 1,750 630,000 eggs with a mean of 39,553 eggs. The result also showed that there exist a weak correlation (r < 0.5) between fecundity and total length, fecundity and carapace length and/or body weight for M. vollenhovenii from Badagry and Lagos Lagoons while M. vollenhovenii from Epe Lagoon had a strong correlation (r > 0.5). The egg diameter from the three lagoons ranged from 465 780 µm while the Gonado-Somatic Index (GSI) from the three lagoons ranged from 0.78 14.29 %. In this study, it was observed that males of M. vollenhovenii occurred more in Badagry and Epe Lagoons, which might be due to the freshness of the environment while females were predominated in Lagos Lagoon, due to their search for a spawning ground especially when the salinity of the water is high. This study would therefore, serve as a basis upon which further researches on the reproductive biology of M. vollenhovenii could be based.
Key words: Sex ratio, Fecundity, Egg stages, Gonado-Somatic Index, Macrobrachium species.