Reproductive cycle of the mangrove prosobranch, Pachymelania fusca (Gmelin, 1791) var. quadriseriata (Gray) (Gastropoda: Melaniidae) in Lagos, Nigeria.

The reproductive activity of the mangrove prosobranch, Pachymelania fusca was studied monthly in the University of Lagos mangrove swamp, at the edge of the Lagos lagoon. The reproductive cycle was analysed from November 2003 to March 2005 by histological examination and macroscopic features of the gonads. Four gonadal stages are described: recently spawned, unripe, ripe and spawning gonads. Sex ratio obtained during this study was 1: 0.95; (51.24% males, 48.76% females). On month by month, there were three peaks when there were more females than males; October-December 2003, October-December 2004 and February-March 2005. Histological analyses revealed that reproductive activity was synchronous in both sexes, from October to March, the exact timing appearing to vary in successive years by about one month. Spawning occurred at end of rainy season and the beginning of the dry season, when the salinity of the water ranged from about 0.5-25.5 psu and surface water temperature was 29-30 degrees C. The resting phase was April to June, during the rainy and low salinity season when the mudflat is flooded and the water turbulent. It is suggested that the species limits its breeding season to a period when there is sufficient food available and when the eggs and larvae will not be washed away.