Spawning Seasonality

Spawning is often linked with temperature extremes, water-boune gametes or abrupt changes in the environments, with pearl oysters from temperate regions generally displaying more distinct, regular spawning seasons. Spawning in tropical oysters is not limited to any single season and protracted spawning may occur throughout the year. Although warm water controls development, cold water will induce spawning (Alagarswami 1970). Maximum spawning intensity in Pinctada margaritifera is usually in summer and winter, but varies between spawning locations and years. Spawning seasons vary considerably from region to region and range from only once a year (March through September) in the Red Sea (Crossland 1957), twice a year in Australia (July–August and November) and five times in French Polynesia (Thielley et al. 1993). Although temperature is the main factor determining sexual development and initiating spawning, the frequent occurrence of limited spawning outside of the recognized breeding periods suggests that groups of pearl oysters respond to local stimuli (Tranter 1958). These can include a reduction in salinity, food availability, changes in currents, calm seas, crowding and other stressors such as handling and exposure to the air.