7977

• UCREFRP Catalog Number: 7977
• Author: Muth, R. T. and J. B. Ruppert
• Title: Effects of Two Electrofishing Currents on Captive Ripe Razorback Sucker and Subsequent Egg Hatching Success
• USFW Year: 1996
• USFW - Doc Type: North American Journal of Fisheries Management
• Copyright Material: YES

MANAGEMENT BRIEFS
tebrae or less (class 2), or wounds on spine greater
than the width of two vertebrae (class 3).
Results
. Tetany was induced in all shocked fish during
treatment, but those exposed to CPS continued to
quiver after they appeared to be tetanized, whereas
fish subjected to the 60-Hz current did not. All
males and females exposed to either current ex-
pelled gametes during shocking; each female ex-
pelled at least several hundred eggs. No external
hemorrhages were observed on any fish.
Necropsy and X-ray examinations revealed ev-
idence of injuries associated with the spinal col-
umn in two males and two females (50% of fish)
subjected to the 60-Hz current and one female
(14% of fish) exposed to CPS. Each injured male
had a class 3 hemorrhage dorsal to the spinal col-
umn and slightly anterior to the origin of the dorsal
fin. One female exposed to the 60-Hz pulse fre-
quency had two vertebral injuries posterior to the
dorsal fin: one rated as class 2, located slightly
posterior to the anal fin and involving two vgrte-
brae, and the other rated as a class 3 fracture, lo-
cated slightly posterior to the dorsal fin and in-
volving three vertebrae. There was evidence of a
class 1 hemorrhage dorsal to each vertebral injury.
The other two females with injuries each had a
class 2 hemorrhage dorsal to the spinal column
and slightly posterior to the origin of the dorsal
fin. No injuries associated with the spinal column
were evident in control fish, and no damage to
internal organs was observed in any shocked or
control fish.
Some of the preserved unfertilized eggs from
each treatment replicate and the control had rup-
tured chorions (8-12% of each 50-egg subsample).
For all treatment replicates and the control, max-
imum diameter averaged 1.8 mm (range, 1.5-2.0
mm) for unfertilized eggs and 2.1 mm (range, 1.8-
2.3 mm) for water-hardened eggs.
Eggs in all lots began hatching at about 114 h
postfertilization, and hatching was completed
about 10 h later. Hatching success in egg lots of
treatment replicates exposed to either current was
significantly lower than that in egg lots of the con-
trol. However, the difference in mean egg-hatching
success between treatment currents was not sig-
nificant. Egg hatch ranges were 21.0-35.4%
(mean, 25.9%) for the control, 3.6-16.6% (mean,
10.6%) for the 60-Hz treatment, and 2.0-10.2%
(mean, 4.9%) for the CPS treatment.
Discussion
475
The differences we observed in rate and severity
of electroshock-induced injuries between the two
currents were consistent with results obtained from
similar studies on other fishes by Fredenburg
(1992) and Sharber et al. (1994). They demon-
strated that CPS was less harmful to fish than sim-
ple DC pulse frequencies of 30 Hz or more. The
only other published study on effects of pulsed DC
on large-river fishes native to the Colorado River
basin was by Cowdell and Valdez (1994). They
found localized hemorrhaging along a portion of
the spine in 5% of 40 adult roundtail chub Gila
robusta (219-404 mm total length) collected from
the upper Colorado River with a boat-mounted
Coffelt VVP-15 electrofisher (square waveform;
40 Hz; 20% duty cycle; 120-V, 8-A output).
Other researchers have investigated the effects
of electroshocking ripe male and female fish and
found substantial reductions in the viability of fer-
tilized eggs through the eyed stage. Newman and
Stone (1992) exposed ripe walleyes Stizostedion
vitreum to 400-V, 120-Hz, pulsed DC (quarter-sine
waveform) and, although no supporting data were
given, suggested that reduced egg viability was
possibly caused by rupture of unfertilized eggs or
decreased sperm motility. Marriott (1973) sus-
pected that the overall lower egg viability for pink
salmon Oncorhynchus gorbuscha shocked with
110-V, 60-Hz AC for 5 s was at least partly caused
by observed damage to the internal organs of some
females that loosened unfertilized eggs from ovar-
ian tissue and bathed them in body fluids. He con-
cluded that shocking had no effect on males. Al-
though we did not observe injuries to internal or-
gans of shocked female razorback suckers or ob-
vious treatment-related damage to their eggs, we
cannot rule out the possibility of undetected dam-
age to eggs or decreased motility of the sperm of
shocked males. Although mean percent hatch of
eggs in our control was relatively low (25.9%), it
falls within the reported range of 22.5-54.7% for
artificially fertilized razorback sucker eggs in
hatcheries (Inslee 1982; Hamman 1985) and was
15.3-21.0% higher than the mean percent hatch of
eggs in shocked groups.
Our results suggest that electrofishing spawning
aggregations of razorback suckers could injure
adults, cause premature expulsion of gametes from
fish during exposure to electric fields, and signif-
icantly reduce egg-hatching success. Effects of
electrofishing on natural reproductive behavior of
razorback suckers are unknown. Given the pre-