Abstract
Breeding pairs of convict cichlids, Cichlasoma nigrofasciatum, and rainbow cichlids, Herotilapia multispinosa, were observed at night with an infrared visionscope to determine the extent of nocturnal egg care. In both species, females fanned eggs at night. The position of the female while fanning differed between day and night; the female's snout was close to the eggs, at night, and her lowered pelvic fins often brushed against the eggs. This suggests that she used olfactory and/or tactile cues to maintain proximity to her eggs in the dark. The percentage of time spent fanning and the duration of fanning bouts were always higher at night than during the day. The difference was caused partly by a direct effect of darkness and partly by an endogenous circadian rhythm, as demonstrated by experiments where dark pulses were given in the middle of the day, or where constant light and constant darkness were used. High activity levels throughout the night may represent a substantial energetic cost and may explain why females often fail to gain weight during the parental cycle.
Published Version
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