The anticipation of night by fry-retrieving convict cichlids

Abstract

Abstract. Every day at dusk, many parental cichlids 'retrieve' their fry: they take wandering fry into their mouth and spit them into a previously dug pit. The present study investigated the relative importance of illumination changes and endogenous clock mechanisms in the daily timing of fry-retrieving behaviour in convict cichlids, Cichlasoma nigrofasciatum. Even when night onset was abrupt, most female cichlids were able to anticipate night: they started retrieving 0-12 min before night onset. Retrieving was more pronounced, however, when night onset was reliably preceded by a 15-min period of dim illumination. Dim illumination at other times of the day elicited no fry-retrieving response. When complete darkness was imposed in the middle of the day, retrieving took place but at lower levels than during the first 15 min of the preceding night. These results indicate a dual role of light levels and endogenous clock mechanisms in the anticipation of night by fry-retrieving convict cichlids. Light levels alone may not be sufficient because dusk is not the only time when light levels change, and endogenous clocks alone may not be sufficient because they are not accurate enough.