The effect of light on activity and growth of Atlantic halibut, Hippoglossus hippoglossus L., yolk-sac larvae

The growth and activity of Atlantic halibut, Hippoglossus hippoglossus L., yolk-sac larvae exposed to light of differing intensities and wavelengths w ere investigated every fifth day. The experiments were conducted at 6 degre es C from day 1 until day 34 post hatch. Four intensities of constant white light (2.0, 0.3, 0.03 and 0.005 mu E m(-2) s(-1), lambda(max) 590 nm), and constant coloured light of equal intensities (0.03 mu E m(-2) s(-1)) in th e blue, green and red spectrums (lambda(max) 450, 560 and 670 nm, respectiv ely) were used. In addition to a control treatment in constant darkness, on e treatment was incubated in a 12:12 h light:dark photoperiod. The light tr eatments did not have any discernible effect on the total length, myotome h eight, dry weights or yolk conversion efficiencies. The most intense white light resulted in an increased activity on days 24 and 30 post hatch, resul ting in a temporarily reduced length and myotome height for the larvae in t hese groups compared to the other treatments. Larvae from all treatments we re of the same size 34 days post hatch. The dry weights of the larvae and y olk-sacs were unaffected by light treatment. The activity increased indepen dently of light treatment until 120 degree-days, and thereafter, the strong est white light resulted in an temporarily increased activity. The distribu tion of activity changed independently of light regime in the beakers durin g development.