Temperature and photoperiod drive Crassostrea gigas reproductive internal clock

This study examined the gametogenic cycle of Crassostrea gigas in controlled conditions over one year, with a focus on the initiation of gametogenesis. This work analysed also the role of temperature and photoperiod in the regulation of oyster reproduction. Broodstock were maintained in natural (NC), accelerated (AC) and perpetual winter (WC) conditions of temperature and photoperiod, with feeding ad libitum. Qualitative and quantitative analyses of the reproductive pattern were performed using biometric measurement approach, sex ratio determination, histology and a gonad filling index. Each experimental treatment led to different strategies for growth and resource allocation. The gametogenic cycle, appeared entirely modulated, accelerated or delayed, by coupled temperature/photoperiod parameters. Temperature played a key role in gonial mitosis regulation. Gonia proliferation was set off and sustained by winter temperature (8–11 °C) whatever the physiological state of oysters. Maturation of germ cells appeared to be a function of temperature and could proceed at low temperature, while ripe oysters were obtained at 8 °C in winter conditioning. The three conditioning methods used in this study, allowed the production of gametes throughout the year, including in the autumnal resting period. Moreover, stocks of ripe oysters could be maintained at low temperature during several months to produce spat when desired for aquaculture production.