Adult per3-luciferase transgenic zebrafish (Kaneko and Cahill 2005 (link); Kaneko et al. 2006 (link)) were dissected to investigate direct photoreception in multiple tissues. Specifically, small tissue pieces of brain, fin, gill, gut, liver, muscle, skin, and testis were placed into 96-well dishes, while eye, heart, and pineal and pituitary glands were placed in whole-organ culture and incubated in Leibovitz (L15) media, supplemented with 15% fetal calf serum, penicillin/streptomycin (50 U/mL), gentamicin (50 mg/mL), and 0.5 mM beetle luciferin (Promega). Subsequently, plates were exposed for up to 6 d to two different lighting regimes comprising (1) a forward light cycle consisting of 12 h of light, followed by 12 h of dark (LD), or (2) a reverse light cycle comprising 12 h of dark, followed by 12 h of light (DL), before being transferred into constant darkness (DD) for up to 7 d. A bioluminescence reporter assay measured gene activity during the entire 2 wk of the experiment (LD or DL into DD) on a Packard TopCount NXT scintillation counter at 28°C.