Spawning time of black sea bream Acanthopagrus schlegelii, related to underwater photoperiodism in oyster farms

The embryonic development times, spawning timing and hatching rates of the black sea bream Acanthopagrus schlegelii were examined to investigate the potential effect of seawater temperature, tides and photoperiod on the reproductive rhythm of this species in Hiroshima Bay, Japan. Low temperatures decreased hatching rates and extended the hatching time, and the minimum temperature threshold for hatching was 15 degrees C. Back-calculated spawning times indicated that the peak of spawning occurred just before sunset and the reduction in diurnal light intensity around the oyster rafts acted as a trigger for spawning. In contrast, no correlation was found between spawning rhythms and tidal cycle. The results highlight the important role of oyster farms in the reproductive cycle and population dynamics of A. schlegelii in Hiroshima Bay, the main spawning ground for this species in Japan. The study findings provide insights for the sustainable management of this important sparid species.