Daily spawning and locomotor activity rhythms of European sea bass broodstock (Dicentrarchus labrax)

Fish have an internal biological clock that drives their daily rhythms, including those of feeding and reproduction. The European sea bass has been reported to exhibit a phase inversion of its diel feeding pattern: nocturnal in winter (coinciding with the spawning period) and diurnal during the remainder of the year. In this study, we investigated the locomotor activity of sea bass during the spawning and resting periods as well as the possible existence of a daily spawning rhythm by calculating the number of eggs (and their viability) released every hour. The results showed that sea bass locomotor activity was clearly nocturnal (68 ± 4.3% of the daily activity displayed at night) during the spawning season and mostly diurnal (65.5 ± 7.5% of the activity displayed during the day) out of the reproductive period. Spawning occurred during the dark phase with two peaks, 6 and 11 h after lights off. Egg viability was highest in the batch released near the spawning peaks. These findings could be useful for optimizing egg production and to improve hatchery practices, which should take into account the reproduction rhythms of sea bass.

► We investigated daily rhythms of locomotor activity and spawning in sea bass.
► Activity rhythms were nocturnal during spawning, but diurnal in the resting period.
► Spawning occurred at night with two peaks at 6 and 11 hours after lights off.
► Egg viability was highest in the batch released around the spawning peaks.