Water temperature is a crucial environmental factor that influences reproductive function of abalone. Broodstock conditioning exposed to effective accumulative temperature (EAT) is a common practice in abalone hatcheries. To understand the molecular mechanism underlying the regulation of gonadal maturation and reproduction of Haliotis discus hannai exposed to EAT and induced spawning period, changes in expression of neuroendocrine genes encoding two
gonadotropin releasing hormone (Hdh-
GnRH,
GnRH-like
peptide),
GnRH receptor (HdhGnRH-R),
serotonin receptor (5-HTHdh) and Hdh-
APGWamide in neural ganglia and gonadal tissues were examined. Gonadosomatic index (GSI) was significantly increased with increasing EAT °C-days. Expression levels of Hdh-
GnRH,
GnRH-like
peptide, HdhGnRH-R, 5-HTHdh and Hdh-
APGWamide mRNA were significantly increased with increasing EAT °C-days in
ganglion (where the gene synthesized) and gonadal tissues. The significant increase in
mRNA expression of each examined gene started from EAT 500 to 750°C-days, reached an initial peak at 1000°C-days, suggesting gonadal maturation started from the onset of EAT and slowly continued until 750°C-days, then at 1000°C-days reached to initial peak developmental period. The maturation reached to spawning state at 1000°C-days and peaked at 1500°C-days. Hdh-
GnRH showed significantly higher
mRNA expression in pleuropedal
ganglion and branchial
ganglion, whereas
GnRH like
peptide showed higher expression in cerebral
ganglion, and HdhGnRH-R, 5-HTHdh and Hdh-
APGWamide showed higher expression in pleuropedal
ganglion. All genes were expressed higher at higher EAT °C-days. During induced spawning period, higher
mRNA expression of examined genes was observed at the time of spawning; however, a sharp decrease occurred after spawning, suggesting that these genes are involved in spawning activities. Taken together, these results indicate that an increase of EAT °C-days can increase expression of neuroendocrine genes and enhance gonadal maturation. Besides all these genes are involved in the process of spawning induction, and increase of GSI has a positive correlation with the increase of gene expression.