The grey mullet Osteomugil speigleri (Bleeker) is of commercial importance in Porto Novo. Maturity and spawning of this mullet was studied by observations on fish gonads collected from January to December, 1977. It was found to have an extended breeding period from January to May, spawning only once during the breeding season as evidenced by (1) specimens with oozing gonads from January to May, (2) clearly separated mature group of ova from the immature stock and (3) gonado-somatic index and relative condition factor.

Males were found to attain maturity earlier than females. Fishes with maturing (stage III) gonads were only available in the Vellar Estuary, Killai Backwaters and Pitchavaram mangrove areas, whereas mature (stage IV), oozing (stage V) and spent (stage VI) fishes were available only in the inshore waters. This evidently indicates that O. speigleri breeds in the inshore waters and not in the estuary.