Doctoring FishNew Vaccines for
Samples of wild channel catfish harvested by aquatic pathologist Joyce Evans
from a Chester River, Maryland, net pen will be assessed for overall health and
the presence of microorganisms.
Like people, fish have their share of diseases and need vaccines to keep
them healthy. Agricultural Research
Service scientists at Auburn, Alabama, have developed several of these
vaccines and are now closing in on one that protects fish from a
The agency's Aquatic Animal Health Research Laboratory is developing a new
vaccine against Streptococcus iniae, says Phillip H. Klesius, who
heads the Auburn unit. "S. iniae is an emerging bacterial
pathogen in cultivated tilapia, hybrid striped bass, rainbow trout, yellowtail,
eel, and turbot. Worldwide, streptococcal infections are reported in 22 fish
species, both cultured and wild," he says.
S. iniae is recognized as one of the most problematic bacterial
pathogens in intensively cultured tilapia and hybrid striped bass in the United
States. Development of good health management practices and a vaccine to
control it is a superior approach to using antibiotics or chemicals, Klesius
Klesius, ARS molecular biologist Craig A. Shoemaker, and ARS aquatic
pathologist Joyce J. Evans are co-developing the vaccine. This team combines
unique expertise in fish disease prevention. Members conduct basic research to
understand immunity, transmission, and infectionparticularly in hybrid
striped bass and tilapia.
"We found the S. iniae bacterium possibly enters the nostrils
of the fish from the water," says Evans, who is with the Auburn unit but
based at Washington College in Chestertown, Maryland. She is researching fish
health problems associated with fish kills and aquatic pathogens. "Finding
out how bacteria enter and travel through the fish may aid in development of an
effective vaccine," she says.
The higher the density of cultured fish, the more easily S. iniae
is transmitted and the higher the mortality, says Shoemaker. "Signs of the
disease in fish are abnormal behavior such as erratic swimming, whirling motion
at the surface of the water, darkening of the skin, blindness, popeyes, and
small lesions on the body, fins, and anus."
Antibiotics are currently used to control the streptococcal disease in fish.
Surprisingly, the team's research indicates there are certain negative effects
on fish health and immunity after antibiotic treatment for S. iniae.
This indicates that antibiotic treatment suppresses streptococcal disease signs
but doesn't completely eliminate the bacterium from treated fish.
Vaccine to the Rescue
These new findings are important determinants for developing a successful
vaccine to fight S. iniae, which causes $150 million a year in losses.
The ARS scientists are designing it to provide lifelong protection. In
laboratory studies, it has reduced mortality in tilapia and hybrid striped bass
by more than 80 percent.
Popular in Asian countries, tilapia is showing up on more U.S. menus. Since
1997, U.S. fresh and frozen tilapia imports have increased 28 percent and U.S.
tilapia cultivation is expanding steadily. Hybrid striped bass consumption and
production through cultivation are also increasing rapidly because of rising
consumer demand for this excellent-tasting fish.
"We are currently developing plans to test the vaccine on a larger
scale throughout the United States," Klesius says. "We are testing
effectiveness of both injection and the bath immersion immunization that gives
fish farmers more flexibility. This vaccine could potentially save producers
Blood obtained nonlethally from wild channel catfish will be used to develop
monoclonal antibodies against infectious disease agents.
The ARS team has filed for a patent on the new vaccine for use in both small
and larger sized fish.
More Catfish Disease Protection
Klesius and Shoemaker recently developed the first approved modified
live-bacterium fish vaccine, one that protects young channel catfish against
enteric septicemia (ESC). A major catfish disease caused by the bacterium
Edwardsiella ictaluri, ESC costs catfish farmers as much as $60
million a year in losses. This new vaccinemade of a live E.
ictaluri organism rendered unable to cause diseaseprevents
infection. ARS has filed for a patent on it.
Also called "hole in the head," enteric septicemia is
characterized by lesions and holes in the fish's cranium, as well as by a
bright-red color at the base of its gills and belly. It accounts for 70 percent
of disease losses in catfish but has never been associated with human
"In field studies," Shoemaker says, "the ESC vaccine reduced
catfish mortality by 80 percent."
Not To Forget Tail Rot
Another emerging problem is the bacterium Flavobacterium columnare.
It causes columnaris disease, sometimes called peduncle disease or tail rot (in
aquarium species, cotton-wool mouth), a significant source of economic loss in
cultivated catfish, hybrid striped bass, and other fish species. Currently,
there is no means to successfully control this infection, says Klesius.
The scientists at Auburn are evaluating various vaccine formulations to
prevent it. They have found that fish surviving columnaris disease are
resistant or immune to reinfection. This shows that a future vaccine is
Klesius and colleagues are also researching fish behavior and health
problems related to fungal, algal, bacterial, and chemical toxins that have
been implicated in fish kills in U.S. coastal waters. They have developed
unique methods to culture brain cells from fish and determine the types of
brain cell injury caused by toxins from infectious and noninfectious agents.
"We hope this research provides new insights into behavior, health, and
immunity in wild and cultured fish exposed to toxic agents and pollutants found
frequently in the United States. This research is a necessary part of ensuring
a safe food supply," says Klesius.By
Agricultural Research Service Information Staff.
This research is part of Aquaculture, an ARS National Program (#106)
described on the World Wide Web at
Phillip H. Klesius and
Craig A. Shoemaker are at the
USDA-ARS Aquatic Animal Health Research Laboratory, 990 Wire Rd., Auburn, AL
36831-0952; phone (334) 887-3741, fax (334) 887-2983.
Joyce J. Evans, USDA-ARS
Aquatic Animal Health Research Laboratory, Washington College, 300 Washington
St., Chestertown, MD 21620; phone (410) 810-7151, fax (410) 810-7451.
"DOCTORING FISHNew Vaccines for
Aquaculturists" was published in the October 1999 issue of Agricultural