PAT-UC Covers - California Sea Grant - UC San Diego

Hedgecock’s analyses suggest that stocking, when used as a fishery management
tool, is highly likely to erode genetic diversity of supplemented populations,
particularly if it is successful at substantially increasing fish abundance. Somewhat
paradoxically, however, hatchery releases can actually boost the genetic variability
of small remnant populations, such as endangered salmon. Based on his findings,
Hedgecock has recommended that, as a matter of course, hatcheries should tag all
fish and document their parentage before releasing them so that their interactions
with wild fish can be evaluated through time.
Strange Disease at Hatchery Explained
With Sea Grant funding, fish pathologist Ronald Hedrick of UC Davis was able
to determine the cause of a disease at the state’s white seabass hatchery that led
to the destruction of thousands of fish: a rickettsial pathogen called Piscirickettsia
salmonis, infamous for plaguing salmon farms. Before this Sea Grant research, the
consensus within the scientific community was that P. salmonis could infect only
salmon, hence the pathogen’s Latin name.
The pedigree is also being used to
investigate whether sturgeon can be
selectively bred for superior caviar weight,
grade, color, firmness and yield. If so,
the industry’s value would stand to rise
significantly, particularly given the status of
wild sturgeon populations and severe caviar
shortages from the Caspian Sea region.
These conditions, and sky-high prices for
specialty caviars like beluga, are fostering
greater consumer acceptance of cultured
products (see project R/A-109).
Genetic Ramifications of Stock
Enhancement
With many fisheries in decline, state
resource agencies are considering stocking
as a way to replenish depleted populations.
There are, however, concerns that this
practice could reduce genetic variability,
and hence the fitness of wild fish. Sea Grant
funded geneticist Dennis Hedgecock of
UC Davis to calculate the “effective size” of
the broodstock at the state’s white seabass
hatchery, which releases tens of thousands
of fish each year.
Subsequent Sea Grant-funded experiments by Hedrick have shown that P.
salmonis can indeed be transmitted between salmon and white seabass. Among
other things, this finding highlights the potential for farms to infect wild fish and
vice versa. Because of Hedrick’s research, the hatchery now tests juvenile seabass
for P. salmonis before releasing them, a procedure that dramatically reduces the
chances of spreading disease.
The molecular tools advanced in this project, including the development of an
early detection test, can easily be adapted for large-scale commercial use. A vaccine
for the disease is currently under development, and Hedrick’s work has received
widespread media attention.
Migrating California Salmon (Photo USFWS)
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California Sea Grant: 1998-2003