Magel et al.: Recovery of visual function in Hippoglossus stenolepis after exposure to bright light 
571 
B 
Log (illumination) 
Log (illumination) 
Figure 2 
Comparison of responses to increasing illumi¬ 
nation or light intensities (I, measured in log 
candela/m 2 by using electroretinography) be¬ 
tween a control group of Pacific halibut (Hip¬ 
poglossus stenolepis) and another group of Pa¬ 
cific halibut 2, 4, 6, and 10 weeks after light 
exposure (n=8-10). To construct voltage in re¬ 
lation to log light intensity (V-log I) response 
curves, light intensities were increased in 0.2 
log-unit steps from levels that produced no 
measurable responses to those that produced 
maximal responses (p-max). The data are re¬ 
ported both as voltage and log-normalized by 
expressing the average response to an intensity 
step as a percentage of the maximum observed 
average response. V-log I response curves were 
created by using voltage data and log-normal¬ 
ized data expressed by the average response to 
an intensity step as a fraction of the maximum 
observed average response. All data points are 
those recorded from the right eye. Data points 
represent means ± standard error. 
crease in activity from minute 5 to 6 (Tukey’s HSD : , 
P< 0.05, for 3xl0~ 3 and 3xl0 -4 pmol-m _2 -s -1 ) (Fig 4, A 
and B). This response diminished as ambient light lev¬ 
els decreased, and no significant increase in activity 
was observed from minute 5 to 6 at the 2 lowest ambi¬ 
Figure 3 
Comparison of responses to increasing illumination 
or light intensities (I, measured in log candela/m 2 ) 
by using electroretinography [ERG] between a con¬ 
trol group of Pacific halibut (Hippoglossus stenol¬ 
epis) and another group of Pacific halibut after 2, 
4, 6, and 10 weeks of recovery from light exposure 
(n=8-10). To construct voltage in relation to log light 
intensity (V-log I) response curves, light intensities 
were increased in 0.2 log-unit steps from levels that 
produced no measurable responses to those that 
produced maximal responses. The data were log 
normalized by expressing the average response to 
an intensity step as a fraction of the maximum ob¬ 
served average response. Each curve was then fitted 
with a second-order polynomial equation because 
the ERG response curves generally indicated a sig¬ 
moid response to light intensities. Light intensities 
required to produce a response 50% of the maximum 
response were taken from the predicted values pro¬ 
duced from the quadratic equation for each model. 
All data points were those recorded from the right 
eye. Data points represent means, and error bars 
indicate standard errors of the means. 
ent light levels (Tukey’s HSD: P>0.05, for 3xl0~ 5 and 
3 X 10 -6 pmol-m _2 -s _1 ) (Fig 4, C and D). 
Discussion 
Prior research (Brill et al., 2008) has shown that expo¬ 
sure to simulated sunlight (i.e., imitating the situation 
experienced on the deck of a vessel) impairs the retinal 
function of Pacific halibut. The authors speculated that 
exposure to simulated sunlight resulted in damage and 
apoptosis of photoreceptor cells containing the longer 
wavelength (520-540-nm) absorbing visual pigments. 
A predominance of receptors with maximal sensitivity 
in the green wavelengths is characteristic of coastal 
and continental shelf species (Levine and MacNichol, 
1979; Bowmaker, 1990). If permanent, a deficit in these 
retinal receptors could have negative consequences for 
post release foraging success, somatic growth, repro¬ 
ductive success, and ultimately survival. 
