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

474
MUTH AND RUPPERT
240-Hz, 2.6-ms pulses, which results in a 12% duty
cycle. Each control unit was set at 200 V, and
output was measured at 0.45 A. Typical output
from a VVP-15 during electrofishing on the Green
and Colorado rivers in Utah, at conductivities of
300-600 µS/cm, is 200-300 V and 5-7 A (T.
Chart, Utah Division of Wildlife Resources, per-
sonal communication).
The treatment chamber was a 227 cm long X
53 cm wide X 53 cm deep fiberglass tank with full
cross-sectional steel-plate electrodes placed par-
allel 191 cm apart to provide homogeneous electric
fields with a peak-voltage gradient of 1.0 V/cm,
as measured by an oscilloscope. According to data
summarized by Snyder (1992), a peak-voltage gra-
dient of 1.0 V/cm should be sufficient to induce
at least narcosis in many fishes. Water in the tank
was 47 cm deep and 20°C. Conductivity was 610
µS/cm, which approximated mean conductivity in
the Green River near razorback sucker spawning
areas upstream of Jensen, Utah, during late April
through May, the period when peak spawning of
razorback suckers usually occurs (T. Modde, U.S.
Fish and Wildlife Service, personal communica-
tion). A plastic mesh holding basket, 90 cm long
X 38 cm wide X 37 cm deep, was suspended mid-
way between the electrodes to confine fish during
treatment and keep them away from the electrodes
and the treatment chamber walls and bottom.
Treatment with either current was replicated
twice, and each replicate consisted of two males
and two females, except for one replicate subjected
to CPS that consisted of two males and one female.
There was one control consisting of two males and
two females. Each group of fish was randomly
assigned to treatments or control. Control fish were
handled in the same manner as shocked fish but
without exposure to an electric current. Fish in
each treatment replicate were placed one at a time
in the holding basket with their head toward the
anode and subjected to either current for 10 s, an
exposure time used in other investigations (e.g.,
Dwyer and White 1995) and one that might be at
least occasionally expected when electrofishing.
Observations were made on fish behavior and con-
dition before and during treatment. Immediately
before and after treatment, each fish was examined
for external evidence of hemorrhaging (bruises or
brands).
Gametes were manually stripped from fish in
each treatment replicate or the control and com-
bined for egg fertilization. Samples of eggs were
taken before fertilization and immediately after
water hardening and preserved in 10% formalin.
Subsamples of these eggs (N = 50) were later ex-
amined for evidence of obvious damage (e.g., rup-
tured chorion) and measured (maximum diameter)
under a stereo-zoom dissecting microscope. After
stripping, fish were immediately euthanized with
an overdose of tricaine methanesulfonate (MS-
222), labeled as to treatment, and placed in an
ultracold freezer at -84°C for later internal ex-
amination. Fertilized eggs from each treatment
replicate or the control were placed in separate
plastic bags that were inflated with pressurized 02,
sealed and transported to Colorado State Univer-
sity, Fort Collins.
In the laboratory, samples of eggs from each
treatment replicate or the control were divided into
5 (shocked replicates) or 10 lots (control), each
with 500 eggs. Each lot of eggs was placed in a
separate incubation basket that was randomly po-
sitioned in a flow-through trough receiving well
water at 18°C. Eggs were examined at least twice
daily during incubation, and obviously dead eggs
in each lot were recorded and removed to reduce
spread of fungus. Time of hatching (hours post-
fertilization) and hatching success were recorded
for each lot of eggs. Weighted analysis of variance
was used to compare mean egg-hatching success
among treatments and the control because of the
unequal number of egg lots. Fisher's pairwise com-
parison test was used to identify significant dif-
ferences (P <- 0.05) between individual means.
For the internal examination of adults, fish were
partially thawed, X-rayed dorsally and laterally
(left side) with a portable MinXray® model X750-G
on 3M® medical imaging film (35 X 43 cm), and
necropsied. The X-ray plates were inspected for
evidence of damage to vertebrae. Necropsy con-
sisted of filleting fish along both sides of the spine
and then examining the spinal column and sur-
rounding musculature for evidence of hemorrhag-
es. Fish were also opened along the midventral
line, from vent to head, and examined for evidence
of damage to internal organs. Type and severity
of injuries associated with the spinal column were
classified according to criteria proposed by J. B.
Reynolds (Alaska Cooperative Fish and Wildlife
Research Unit), as presented in Hollender and Car-
line (1994). Vertebral injuries were classified as
compression of vertebrae (class 1), misalignment
and compression of vertebrae (class 2), or fracture
of one or more vertebrae or complete separation
of two or more vertebrae (class 3). Hemorrhages
were classified as wounds separate from spine
(class 1), wounds on spine the width of two ver-