Reproductive cycle of the rock oyster, Hyotissa hyotis (Linné, 1758) (Bivalvia, Gryphaeidae) during El Niño 1997-98 and La Niña 1998-99 events at La Ballena Island, Gulf of California, Mexico

Abstract

The reproductive cycle of Hyotissa hyotis during El Niño 1997-98 and La Niña 1998-99 events in La Ballena Island, Gulf of California, Mexico was examined in relation to sea water temperature and chlorophyll a concentration. Every month, from January 1997 to December 1999, 30 adult specimens of H. hyotis were collected at 10 m depth by scuba diving. The specimens’ gonads were subjected to histological analyses and the gonadosomatic index was determined. Spawning occurs during the summer in relation to high temperature, becomes more intense during El Niño and decreases during La Niña events. Sea water temperature was the main factor regulating spawning during these events. The gonadosomatic index is an indicator of gametogenic activity whereas food availability is closely related to gonadic development.