title: Effects of photic environment on ocular melatonin contents in a labrid teleost, the wrasse Halichoeres tenuispinnis.
abstract: The wrasse Halichoeres tenuispinnis is a labrid teleost that exhibits robust circadian rhythms in locomotor activity under constant light (LL). This fish buries itself in the bottom sand during the subjective-night, thereby suggesting that behaviorally it adjusts its circadian clock to avoid photoreception. In this study, we determined ocular melatonin contents of the wrasse under various photic environments and used ocular melatonin to indicate photoreception. Under light-dark (LD) cycles, ocular melatonin contents of the wrasse exhibited a daily rhythm, with higher levels during the dark phase than those during the light phase. The duration of nocturnal melatonin elevation was longer under LD 9:15 than under LD 15:9. Acute exposure to 2-h light during the dark phase resulted in a significant decrease in ocular melatonin at mid-dark in an intensity-dependent manner. However, acute exposure to different intensities of light for 2h during the light phase had only a small effect on ocular melatonin contents at mid-day. Under LL, ocular melatonin contents in the wrasse reared with bottom sand present exhibited circadian rhythms and were significantly higher than those with transluscent acryl pellets on the bottom. These results indicate that the ocular melatonin rhythm in the wrasse is driven both by the photic environment and by a circadian clock, and that the wrasse that buries itself in the bottom sand can perceive low intensity of light.
authors.affiliation: Department of Anatomy, St. Marianna University School of Medicine, 2-16-1 Sugao, Miyamae-ku, Kawasaki 216-8511, Japan. iigo@cc.utsunomiya-u.ac.jp
authors.forename: Masayuki
authors.initials: M
authors.lastname: Iigo
authors.forename: Masaru
authors.initials: M
authors.lastname: Sato
authors.forename: Emi
authors.initials: E
authors.lastname: Ikeda
authors.forename: Shigekatsu
authors.initials: S
authors.lastname: Kawasaki
authors.forename: Fumitaka
authors.initials: F
authors.lastname: Noguchi
authors.forename: Genjirou
authors.initials: G
authors.lastname: Nishi
mesh_terms: D000818:Animals; D002940:Circadian Rhythm; D005123:Eye / Q000737:chemistry*; D008027:Light; D008550:Melatonin / Q000032:analysis*; D009043:Motor Activity; D010473:Perciformes / Q000378:metabolism*; D017440:Photoperiod
chemical_list: D008550:Melatonin