Context Macrobrachium vollenhoveni (Herklots), a freshwater prawn native to Africa, is crucial for aquaculture and subsistence fishing. However, limited data exist on its reproductive biology in Benin’s water bodies. Aims This research aimed to explore the breeding season, size at sexual maturity, fecundity and reproductive output of M. vollenhoveni. Methods Prawns were sampled monthly from May 2015 to October 2016. In total, 1567 females of M. vollenhoveni were collected from the lower Ouémé (864 prawns) and the lower Mono (703 prawns). Key results Findings showed that gonadal maturation starts in March, with peaks in July. Then spawning occurs from July to September, and even October. In both environments, ovigerous females (prawns carrying fertilised eggs in incubation) were frequently captured from July to October, with a maximum proportion in August and September. The spawning period for the two prawn populations in both sampled areas matched with an increase in water volume, salinity and pH. The size at sexual maturity was 8.48-cm total length (TL) for the lower Ouémé population, whereas in lower Mono, it was 9.00 cm TL. Absolute fecundity ranged from 3925 to 31,408 eggs in lower Mono and from 4871 to 25,902 eggs in lower Ouémé. The reproductive output was 12.87% for Mono and 11.94% for Ouémé. Conclusions and implications This research is the first one on the reproductive biology of M. vollenhoveni in Benin and provides vital data for sustainable fishery management of this prawn species in the watersheds throughout the country.