7190

• UCREFRP Catalog Number: 7190
• Author: Muth, R. T., T. P. Nesler and A. F. Wasowicz.
• Title: Marking Cyprinid Larvae with Tetracycline.
• USFW Year: 1988.
• USFW - Doc Type: 89-95.
• Copyright Material: YES

1
MARKING CYPRINID LARVAE WITH TETRACYCLINE 91
values were summed within each sample lot, and
each total was used to compare the intensities of
the marks among the sample lots. For example,
the maximum summed mark-intensity value for a
sample lot of five specimens would be 15.
A second experiment was conducted to examine
the stability of TC deposited in otoliths of fish larvae
that were then exposed to white light. About 300
7-d-old (posthatching) fathead minnow Plmephales
promelas protolarvae were immersed in an aerated,
tris-buffered solution of 350 mg TC/L for 4 h.
Larvae were 5.5-6.5 mm TL, and lapilli and sagittae
were present. After immersion, five larvae were
preserved in 95% ethanol. The remaining larvae
were divided equally into six experimental groups
and placed in 38-L aquaria containing aerated, de-
chlorinatedtap water at 22°C. Then, the larvae were
exposed to white light at replicated treatment inten-
sities of 10, 300, or 1,000 lx (measured at the water
surface) for 12 h/d for 7 d. The two lower light
intensities were achieved by covering the aquaria
with sheets of opaque plastic or fine-mesh screen-
ing. Illumination was provided by paired General
Electric cool white 40-W fluorescent tubes posi-
tioned 20 cm above the aquaria. According to the
manufacturer, these tubes emit light in the 340-
650-nm range. Weber and Ridgway (1967) stated
that tetracycline molecules that were deposited in
fish bone were excited to a fluorescent state by
absorbing UV energy at 360 nm. Larvae were fed
twice daily with live anemia nauplii. Larvae in each
light-intensity treatment were sampled once daily
and preserved in 95% ethanol. Then, otoliths were
extracted, mounted, and examined in the same
manner as for Colorado squawfish larvae.
Results
Mortality of Colorado squawfish larvae was
high for a1136-h-exposure treatments; 71-100% of
the fish in each group died. In the 500-mg/L
treatment for 4- and 12-h, mortality was moderate
(16 and 24% of each group, respectively), then it
stabilized nearly to zero during rearing. For the
remaining treatments, survival was high during
exposure to TC and during rearing. Overall sur-
vival (90-92%) of each treatment group was
higher than that of the control group (79%). Fish
growth, measured in increments of total length,
was similar for all experimental groups. Exposure
to TC had no obvious effect on fish development
or behavior.
Fluorescence was visible externally when
whole treated Colorado squawfish Larvae were
scanned with UV light. The entire bodies of larvae
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B
FIGURE i.-A. Externally visible fluorescent marks
(arrows) on preopercal and subopercal bones of a Col-
orado squawfish larva (10.7 mm total length, TL)
scanned with ultraviolet (UV) light 14 d after whole-body
immersion in a 350-mg tetracycline hydrochloride/L
solution for 4 h. B. Untreated control larva (10.5 mm
TL) scanned with UV light.
from all treatments that had been preserved in
ethanol or buffered formalin within 15 d of expo-
sure to TC fluoresced pale yellow. Fluorescence
was most evident in the yolk and gut regions.
Larvae that had been preserved in ethanol re-
vealed distinct yellow fluorescent marks on the
developing dorsoanterior tip of the preopercal
bone and posterior edge of the subopercal bone
(Figure 1). Fluorescent marks on these bones
were not present in larvae that had been pre-
served in buffered formalin. Larvae that had been
preserved 2 weeks or more after treatment re-
vealed externally visible fluorescence that was
indistinguishable from reflections caused by inci-
dent illumination.
The otoliths extracted from larvae that had
been preserved in .ethanol appeared structurally
intact. However, the otoliths of larvae that had
been preserved in buffered formalin had either
disintegrated during storage or degenerated to
thin, transparent disks that crumbled upon han-
dling. These otoliths were unsuitable for micro-
scopic examination. Asteriscus otoliths were
formed in larval Colorado squawfish during the
third week of rearing, and they were not examined
for fluorescent marks.
Readily detectable marks were visible in oto-
liths of all TC-treated Colorado squawfish larvae
examined by UV-light microscopy (Table 1 and