Reproductive Condition and Spawning Induction in the South African Scallop Pecten sulcicostatus

Reproductive condition of Pecten sulcicostatus from False Bay, South Africa, was assessed monthly from August 2010 to November 2011 by determining the gonadosomatic index (GSI) and by monitoring associated histological changes within the gonads. Simultaneous measurement of temperature and chlorophyll a concentrations at the site of scallop collection provided insight into the conditions controlling the reproductive cycle. Direct spawning induction was also attempted monthly, using four spawning techniques: desiccation, food deprivation, thermal shock, and intragonadal injection of the hormone serotonin. The reproductive cycle of P. sulcicostatus demonstrated seasonality in that the GSI was highest from June to September. An increase in bottom temperatures through winter and spring is a likely factor inducing spawning. The highest phytoplankton biomass in summer and autumn is likely to contribute to the winter buildup of gonads. Injection of serotonin was the only method that successfully induced spawning. Gametogenesis occurred in all months, except that oocytes were not released in November and December.