EFFECT OF THREE HATCHERY LIGHTING SCHEMES ON INDICES OF SMOLTIFICATION IN CHINOOK SALMON

Abstract This experiment examined whether photoperiodic changes induce chinook salmon Oncorhynchus tshawytscha to alter various indices of smoltification. The effect of 24 h light, a constant photoperiod of 9 h light: 015 h dark (9L:15D), and a naturally increasing photoperiod on plasma levels of thyroxine and cortisol, hematocrit, condition factor (K), and hepatosomatic index (HSI) was tested during the period of smoltification in chinook salmon. The 24-h-light group grew faster than the other two groups, but was significantly larger than one of the two groups on only three sampling dates. Mean plasma thyroxine and cortisol levels were highest in the natural-photoperiod group and lowest in the 9L:15D group. Mean plasma cortisol levels increased significantly in the increasing and 9L:15D photoperiod groups but were unchanged in the continuous-light group. Mean HSI decreased faster in the natural-photoperiod group than in the other two groups. Mean hematocrit did not change in the natural-photoperiod group...