Reproductive cycles of the bivalve molluscs Anadara trapezia (Deshayes), Venerupis crenata Lamarck and Anomia descripta Iredale in the Sydney region

The female cycle of each species was described from gross gonad appearance, and quantitatively from oocyte counts. Males were assessed from external appearance and histological classification of the gonad. The timing of the male cycle is similar to that of the female in each species, Spawning in A. trapezia and A. descripta is associated with times of maximum phytoplankton availability. A. trapezia breeds during the summer when water temperatures are high; regeneration of the gonad takes place during winter and spring after a resting phase. A. descripta has two spawning peaks, a minor in summer and a major in autumn; regeneration of the gonad occurs from winter to late summer. V. crenata has a prolonged breeding season, with ripe animals occurring throughout the year, although activity decreases during the winter months; regeneration and maturation appear to occur cqntinuously with po resting phase. These reproductive patterns are discussed in the light of factors controlling reproduction in other bivalve species and strategies of other mollusc groups from the Sydney region.