7874

• UCREFRP Catalog Number: 7874
• Author: Ruppert, J. B. and R. T. Muth.
• Title: Effects Of Electrofishing Fields On Embryos And Larvae Of Razorback Sucker - Final Report.
• USFW Year: 1995.
• USFW - Doc Type: \
• Copyright Material: NO

MS-222. Each larva was measured to the nearest 0.1 mm standard length (SL), allowed to
recover from the anesthetic, and returned to the appropriate rearing beaker. Survival of
larvae was monitored daily during the 4-week rearing period. Analysis of variance was
used to compare mean survival of embryos through hatching and mean survival and growth
(SL increment) of larvae among treatments and controls. Fisher's pair-wise comparison test
was used to identify significant differences (P ~ 0.05) between individual means.

Results

Test with Embryos

Eggs in all treatment or control replicates began hatching at approximately 128 h
postfertilization, and hatching was completed about 12 h later. No obvious external
abnormalities were evident in any hatched larvae. Survival of embryos after treatment
through hatching improved with advancing developmental state (Table 1; Figure 1).
Differences in mean survival between developmental stages were significant for all
treatments, except between early tailbud and finfold for the CPS treatment, but not for
controls. Mean survival of embryos at each developmental stage was significantly greater
in controls than in all treatments except the 3D-Hz and CPS treatments at early tailbud and
finfold. Among the 1.2-V/cm, simple-pulse treatments at early tailbud or finfold, mean
percent survival decreased with increasing pulse rate, and differences between the 3D-Hz
(4-ms pulses) and 80-Hz (5-ms pulses) treatments were significant. Within the 50-Hz
treatments at each developmental stage, mean survival decreased with increasing peak-
voltage gradient and was significantly lower for the 10.0-V/cm treatment at early epiboly and
early tailbud.

Tests with Larvae

Pre-swimup larvae in the 50-Hz, 5.0 and 10.0-V/cm treatments were tetanized
(bodies rigid and immobile) immediately upon exposure to electric current, whereas those
exposed to the other electric fields exhibited severe twitching and rapid, undirected
swimming throughout treatment. Larvae in the 3D-Hz and CPS treatments recovered
normal movements almost immediately after current had been switched off, whereas those
in the other treatments laid on the bottom of the nylon-mesh baskets for several seconds
after exposure. No mortalities were observed within 48 h after treatment.
Survival of larvae over the 4-week period after treatment was not affected by
exposure to electric current, but growth was significantly reduced (Table 2). Mean survival
was 92% for control larvae and ranged 85% (50-Hz, 1.2-Vlcm treatment) to 95% (3D-Hz
treatment) for shocked larvae; means were not significantly different. Mean SL of larvae at
beginning of the rearing period ranged 9.4 to 9.73 mm. After 4 weeks, control larvae were
significantly larger than those in all treatments; control larvae grew an average of 3.7 mm
(0.13 mm/d), whereas treatment larvae had grown only 2.0 to 2.5 mm (0.07 to 0.09 mm/d).
The greater mean length (and therefore growth) of control larvae compared to that of
shocked larvae was first detected as a significant difference 14 d after exposure for the
80-Hz treatment and 21 d after exposure for all other groups (Table 2). Differences in
mean length (and growth) of larvae among treatments at each 7 -d interval after exposure to
electric current were not significant.

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