Small Fish for a Large Task
David Hinton Takes His Medaka West to Monitor California's
Drinking Water p.4
Their yolk sacks make the embryos appear larger
than they really are. As they grow, the yolk sacks recede,
then disappear. “Then they will look quite small,” Hinton
says as he stands in his Nicholas School lab. Surrounding
him are various aquarium tanks alive with standard and transparent
medaka at various stages of growth.
Both medaka and zebra fish “have good reasons
for being used, depending on the question you are asking of
them,” he notes. “Because of our years of experience working
with medaka, we continue to work with them.” Richard
Di Giulio, another Nicholas School professor
of environmental toxicology who directs Duke’s
Superfund Basic Research Center, also employs
a third model fish. Called Fundulus, this fish is a North
Carolina resident species and thus extremely useful for evaluating
toxicity questions in local bays and in shore environments.
According to the research proposal for the Orange
County project, medaka have a compressed life cycle that makes
their use particularly advantageous. A “relatively rapid life
cycle is characteristic of these fish. For example, fish are
sexually mature by two months after hatching. This facilitates
assessment of reproduction and development in a short time
frame.” Moreover, “all major classes of chemical carcinogens
have been tested in medaka.”
Plans are to expose the sentinel medaka populations
to water from two Southern California sources: predominantly
surface water originating in the Colorado River, and treated
Orange County effluent. Both standard and transparent medaka
will be exposed to Orange County water for nine months at
a time. To allow for seasonal changes, different populations
will begin their exposure periods at two-month intervals.
Dan Schlenk, the principal investigator for the
Orange County project, is a former postdoctoral student at
the Duke Marine Laboratory
who is now a professor of Environmental Toxicology at the
University of California, Riverside.
Hinton will be training participating Orange
County personnel as well as Schlenk’s UC-Riverside students
on how to detect telltale signs of abnormalities in the living
fish. Hinton will visit the southern California site two or
three times each year to evaluate the study and screen for
responses from their fluorescing genes.
“It has been a pleasure and honor to work with
Dr. Hinton, who has made significant contributions in understanding
the pathobiology of environmental toxicants in various fish
species such as the Japanese medaka,” says Schlenk. “I am
excited about the impact this project will have on drinking
water evaluations in Southern California as well as other
areas of the world exploring water re-use programs for water
conservation.”
At the study’s end, the fish will be sacrificed
and their fixed tissues will be transported for processing
and analysis to the Histopathology Laboratory at North Carolina
State University’s College of Veterinary Medicine. McHugh
Law of NC State will assist Hinton in the final examinations
of the fish. What observers thought they saw in the living
fish will thus be compared with what is revealed by close
examinations of their tissues. This study is considered an
experiment. But if the final pathology results reflect what
the fish seem to be “telling” their human monitors over the
two years, then Hinton says living medaka may eventually become
permanent drinking water pollution monitors for Orange County.
That would be in keeping with the recommendations of a National
Academy of Sciences panel that recommended use of an on line
monitor.
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