Nocturnal parental care and the role of parents in hatching their eggs in the clown anemonefish

Parental care is a critical component of many breeding systems that enhances both parent and offspring fitness. It is widely recognized that parental care varies in quality and quantity in response to variation in offspring need, parental condition, and ecological context. One context that has been underexplored, however, is the presence of extensive parental care at night, with many parental care studies focused on diurnal care. To fully understand the evolution of parental care, both diurnal and nocturnal care must be accounted for. Here, we show that nocturnal parental care exists in the clownfish Amphiprion percula, with males and females actively caring for offspring at night throughout embryo development and during hatching within a laboratory setting. At night, as during the day, males continue to be the dominant caregiver and both parents increase care as embryos mature. However, females provide substantially more care at night than during the day. We also document three new parental care behaviors at night that are not seen during the day: vigorous fanning, vigorous mouthing, and anemone biting. These behaviors are particularly frequent during hatching, and they may serve to assist the hatching process by helping embryos transition from the benthic to the pelagic environment. This study contributes to our understanding of parental care, demonstrating the importance of considering nocturnal care if we are to gain a complete understanding of the evolution of parental care.