Darkness at night during the new moon period alters the expression levels of the clock genes in the brain of a moon-related spawner, the Malabar grouper Epinephelus malabaricus

ABSTRACT Some fish in tropical and subtropical waters exhibit moon-related rhythmicity in their reproduction and migration. We investigated the involvement of the subtypes of cryptochrome (mgCry) in moon-related rhythmicity of the Malabar grouper Epinephelus malabaricus, which spawns around the new moon period. Under natural photoperiodic conditions, the levels of mgCry1 and mgCry2 showed daily variation with peaks at 11:00 and 19:00, respectively, in the diencephalon (including the pituitary), regardless of the moon phase. The weekly changes in mgCry2, but not mgCry1, were moon-dependent, with higher levels around the new moon. When fish were reared under natural moonlight, mgCry2 in the pituitary was higher at 15:00 and 11:00 during the new moon period than the full moon period. Rearing fish under moonlight-exposed or moonlight-blocked conditions resulted in increases in mgCry genes in the pituitary during the night at full moon, suggesting that the pituitary is a target organ of the moonlight-dependent clock system. These findings indicate that mgCry genes in the brain of the Malabar grouper exhibits moon dependency, with changes according to the duration of darkness at night. We conclude that weekly changes in Cry genes in the brain play a role in entraining moon-dependent events in the Malabar grouper.