Hermaphroditism and sex reversal in the four common oviparous species of oysters from the coast of Karachi

In the four common oviparous oysters from the coast of Karachi, Crassostrea rivularis, C. madrasensis, Saccostrea glomerata and S. cucculata, the gonad appeared at the age of 2–3 months, at a length of 0.4–0.6 cm. Sex is determined from the origin and hermaphrodites are rare, their percentage among the population increasing as growth proceeds, but is not affected by changes of the seasons. Incidence of hermaphrodites and changes in sex ratio suggest a change of sex as seen in oysters of temperate zones.