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Fishery Bulletin 106(4) 
of events during capture on sensory function. They are 
commercially and recreationally important demersal 
species caught by hook-and-line and trawl gear along 
the west coast of North America. Because of stringent 
fisheries regulations, both are frequently discarded 
(Pacific Fishery Management Council, 2004; Hannah et 
al., 2008). Black rockfish are a deep dwelling physoclist 
species (Parker et al., 2008) and experience significant 
barotrauma when brought to the surface, including 
severe exophthalmia (Hannah and Matteson, 2007; 
Hannah et al., 2008). Pacific halibut lack a swim blad- 
der and do not suffer apparent injuries associated with 
rapid decompression. Pacific halibut are, however, often 
kept on deck of for 30-60 min during sorting operations 
on commercial trawl vessels before being discarded 
(Davis and Olla, 2001). This time onboard results in 
prolonged exposure to air and direct sunlight. Exposure 
to bright light causes photoreceptor damage in both 
vertebrates and invertebrates (Meyer-Rochow, 1994; 
Wu et al., 2006); and fishes that normally live in dim 
light environments are predicted to be especially prone 
to light-induced damage (Loew, 1976). 
Our objective was to examine changes in visual func- 
tion in black rockfish subjected to rapid decompression 
and in Pacific halibut exposed to simulated sunlight 
with electroretinography. The electroretinogram (ERG) 
represents the summed potentials of various cell types 
within the retina, not just those of the photorecep- 
tor cells. Nevertheless, the ERG is considered a useful 
technique for addressing questions about visual func- 
tion, including the identification of gross visual deficits 
(Brown, 1968). 
Materials and methods 
Black rockfish (37.6-46.3 cm total length [TL] ) were cap- 
tured by hook-and-line in waters off shore of Newport, 
OR (44°33'N, 124°6'W). Efforts were made to collect fish 
from as shallow a depth as possible (<25 m), and only 
individuals showing minimal signs of barotrauma (as 
defined in Hannah and Matteson, 2007) were retained. 
Fish were transported to the Hatfield Marine Science 
Center (Newport, OR). During transport, excess swim 
bladder gases were reduced by inserting a sterile hypo- 
dermic needle through the body wall into the swim 
bladder in any fish that were positively buoyant or that 
showed an inability to maintain vertical orientation. 
In order to be able to identify individuals, all fish were 
tagged with 12 mm x 2.1 mm Destron-Fearing ISO FDX- 
B 134.2-kHz passive integrated transponder (PIT) tags 
(Destron-Fearing, St. Paul, MN). Tags were placed in 
the hypaxial musculature (ventral to the cleithrum at a 
depth of 0. 5-1.0 cm) by using a 12-guage stainless steel 
veterinary needle and a modified syringe as described 
by Parker and Rankin (2003). 
Fish were held for six months in a fiberglass tank 
(3.1 m diameter, 1.0 m depth) before use in experi- 
ments. The holding tank was supplied with seawater 
(flow rate: 20 L/min, temperature: 10-12°C, salinity: 
30-32%o) and maintained under dim fluorescent light 
(0.01 pmol photons/m 2 /s) with a 12-hour photoperiod. 
Fish were fed ad libitum three times per week with a 
mixture of chopped frozen clams ( Spisula solidissima), 
squid ( Loligo opalescens), capelin ( Mallotus villosus), 
and silversides (Menidia menidia). 
Age-0 Pacific halibut (31.8-40.2 cm TL) were cap- 
tured with a beam trawl from Chiniak Bay, Kodiak 
Island, AK (57°40'N, 152°30'W) and shipped to the 
Hatfield Marine Science Center. They were subsequently 
reared for two years before use in experiments in fiber- 
glass tanks (3.1 m diameter, 1.0 m depth) supplied with 
seawater (flow rate: 20 L/min, temperature: 8-10°C, 
salinity: 30-32 %c). The tanks were maintained under 
dim fluorescent light (0.01 pmol photons/m 2 /s) with a 
12-hour photoperiod. Fish were fed ad libitum three 
times per week during the first year and twice per 
week during the second year with a gel food consisting 
of squid, Pacific herring ( Clupea pallasii), pelleted food, 
krill ( Euphausia superba ), amino acid supplements, 
vitamins, and gelatin. 
Rapid decompression experiments with black rockfish 
The rapid pressure change (of 3 atmospheres absolute 
[AT A]) to which black rockfish were subjected was chosen 
to mimic the changes in depth that fish encounter during 
capture by both commercial and recreational fisheries, 
and which have been shown to cause significant baro- 
trauma (Parker et al., 2006, 2008). Pressure changes 
were achieved using a large flow-through hyperbaric 
aquarium system capable of maintaining two groups of 
fish separately at up to 4.25 ATA. This system (described 
by Parker et al. [2006]) produces the same signs of 
barotrauma in captive fish as those observed in wild 
fish subjected to equivalent pressure changes when 
being brought up from depth. Two experimental trials 
were performed. For each trial, three control and four 
treatment fish were placed in the hyperbaric chambers 
and acclimated to 4.0 ATA over a period of seven days 
(Fig. 1). Treatment fish were subjected to a simulated 
capture scenario consisting of a 3.0-ATA pressure drop 
over 90 seconds. Individuals were removed from the 
hyperbaric chamber with a dip net, identified, assigned a 
score to quantify the external signs of barotrauma, and 
then immediately placed back in the chamber for repres- 
surization. These procedures resulted in a simulated 
surface interval (i.e., at 1 ATA pressure) of 10 min, but 
only a brief period (<1 min) out of the water. Treatment 
fish were then repressurized to 4.0 ATA over 30 seconds 
simulating the return to depth after release. Fish were 
held at 4.0 ATA for an additional 20 hours after the 
rapid decompression event, then gradually brought to 
1.0 ATA according to the decompression schedule (Fig. 1) 
developed by Parker et al. (2006). To account for any 
effects of the chamber not associated with rapid pres- 
sure change, control fish were subjected to an identical 
schedule of gradual pressure changes, but not the rapid 
decompression event. After completion of all pressure 
changes, fish were removed from the chambers with a 
