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Fish Disease Research Goes in Many Directions
Kyoung Chul Park has continued his studies on what factors are involved in causing
certain strains of viruses to kill fish while other similar strains don't (National Sea
Grant Technology Grant). The current focus is on two factors. The first is a factor in serum
of apparently healthy trout which inhibits the ability of the virus to replicate. Further
characterization of this substance indicates that it requires the divalent cation magnesium to
be effective, and that the ability to inhibit virus growth in cell culture is limited to some
trout and Pacific salmon cell lines, but that inhibition does not occur in the most commonly
used cell line from chinook salmon. He also found that if some strains of virus were grown
in cell culture for longer periods, they lost their capacity to resist the serum inhibitor.
This may explain why virus grown for long periods in cell culture become avirulent in fish.
A second factor in virulence, related to the above experiments, is the number of times
the virus has been grown in cell culture. Preliminary evidence by others had indicated that
if the virus was grown several times in cells first, it would lose virulence. In an
extensive experiment, Kyoung determined that the virulence of the virus for brook trout was
undiminished even after several cycles of replication in cells. Kyoung is currently
evaluating what changes, if any, have occurred in the genome of the viruses treated by growing
in cells, whole fish, or in the presence of trout serum. They anticipate that changes at the
level of the genome may explain some of the unusual results found in these experiments.
Hamdi Ogut has finished the laboratory portion of his experiments designed to
determine how fish diseases are transmitted. He is currently analyzing the extensive data
generated in these experiments and is writing a computer program to allow him to construct
mathematical models of the disease process in populations of fish.
Tim Miller-Morgan has changed course and has begun on another epidemiologic
research effort in the lab. He is working on a project funded by the Western Regional
Aquaculture Committee (USDA) to determine the pattern of pathogen distribution in wild and
cultured salmonids in the Western U.S. Data on fish diseases in feral and hatchery-reared fish
are currently being gathered from state and federal agencies throughout the West. The
data will be analyzed to determine whether the presence of pathogens in hatchery fish is
correlated with the development of disease in wild fish in the areas where cultured and
wild fish coexist and where infected stocks may have been planted into waters where
pathogens were not present.
The resurrection of studies on the microsporidian parasite of Dungeness crabs has
occurred by dint of the interest of Hal Amogan, a graduate student in the Department of
Microbiology. Hal has started a project to determine the taxonomic status of the pathogen by
study
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