Brill et al. : Effects of rapid decompression and exposure to bright light on visual function in Sebastes melanops and Hippoglossus stenolepis 433 
c/i 
CD 
Wavelenath (nm) 
Figure 3 
Spectral sensitivity curves for black rockfish ( Sebastes melanops ) and Pacific halibut 
(Hippoglossus stenolepis) derived from electroretinogram (ERG) responses to 40-ms 
flashes of incremental wavelengths (10-nm steps). Responses from individual trials 
were normalized by expressing the response to a given wavelength as a fraction of the 
maximal response recorded during that trial. Data points are means ±standard error. 
The spectral response curves of black rockfish were unaffected by rapid decompression, 
whereas the ERG responses of Pacific halibut to green wavelengths (=520-580 nm) were 
diminished by 15 minutes of exposure to simulated sunlight. Color bars (truncated at 
400 and 650 nm) have been added to illustrate the approximate spectral colors corre- 
sponding to the various wavelengths. 
the flicker fusion frequency of Pacific halibut. Within- 
species data were therefore combined to test for cross- 
species differences. The median flicker fusion frequency 
for Pacific halibut (30 Hz) was significantly lower than 
that of black rockfish (49 Hz) (PcO.001, Mann-Whitney 
rank sum Test). 
Spectral curves 
The spectral sensitivity curves of black rockfish and 
Pacific halibut were very similar (Fig. 3). Both species 
showed strong sensitivity to blue-green wavelengths 
(480-590 nm), and a range of responses from 380 nm 
(violet) to 610 nm (orange). There was no appreciable 
sensitivity to the shorter (UV-A, 350-380 nm) nor longer 
(red, >620 nm) wavelengths in either species. 
There was no indication that the spectral sensitiv- 
ity of black rockfish was affected by rapid decom- 
pression (Fig. 3), whereas the spectral sensitivity of 
Pacific halibut was clearly influenced by exposure to 
simulated sunlight (Fig. 3). Vitamin Al rhodopsin 
absorbance templates developed by Stavenga et al. 
(1993) were, therefore, used to further assess these 
changes. In all cases, the templates provided rea- 
sonable fits to the observed ERG data (Fig. 4). The 
parameters showing the largest effects of bright light 
exposure were clearly the ratios of the long wave- 
length to short wavelength photopigment weighting 
factors that are indicative of the relative value of the 
two photopigments to the composite curve. In control 
Pacific halibut, this ratio ranged from 0.75 during the 
day to 0.62 during the night, indicating only a slight 
predominance of the shorter wavelength photopig- 
ment (Fig. 4). In contrast, in Pacific halibut exposed 
to simulated sunlight these ratios were 0.48 and 0.12 
during the day and night, respectively. These results 
indicate a much reduced functional importance of the 
longer wavelength photopigment, especially during the 
night (i.e., approximately 12 hours after exposure to 
simulated sunlight). 
