- Spring viremia of carp virus (SVCV) in North America
Andrew E. Goodwin, Audrey Dukedoms , Craig Radi, Kathy
Kurth, Sue Marcquenski, Robert S. Bakal, Keith Way , and David M.
Stone
Spring Viremia of Carp (SVC) is a rhabdoviral disease of cyprinid
fishes. It is most prominent as a pathogen of farm raised common
carp (Cyprinus carpio) in Europe, but the virus affects
many fish species and has been isolated in South America and the
Middle East. Because it has a significant impact on wild and
cultured fish, SVC virus is one of only 5 fish pathogens listed as
“notifiable” in the 2002 International Aquatic Animal Health Code
of the OIE (Office International des Epizooties). The US has
diverse populations of wild cyprinid fishes, a large aquaculture
industry, and a history of live fish commerce with Europe, but SVC
virus has never been reported on the North American continent. In
April of 2002, an epizootic with clinical signs consistent with
SVC occurred on a koi (Cyprinus carpio) farm in the Eastern
U.S. A virus was isolated on EPC cells and subsequently
demonstrated to be SVCV. The farm is a major wholesale distributor
of koi and goldfish with customers throughout the U.S. Control and
eradication of the disease will be difficult not only because of
the geographic range of these customers, but also because ponds on
the farm drain into several rivers that are used as the water
supply. In May and June 2002, a second apparent outbreak of SVC
occurred in Cedar Lake, Wisconsin, a 500 ha lake more that 2000 km
from the infected farm in the Eastern U.S. Some 10,000 kg of wild
common carp died with clinical signs consistent with Spring
Viremia. There is no evidence of any direct link between Cedar
Lake and the SVC case in the Eastern U.S. Nucleotide sequence
information, from a 495 bp region of the viral RNA coding for the
glycoprotein amplified by RT-PCR, demonstrated that the two
isolates were 98.78% similar to each other and that the Wisconsin
isolate is 97.98% & 98.18% similar to isolates recently obtained
from fish exported to the UK from Asia. The isolates are only 88%
similar to European strains.
- Pathogenicity of morphologically and genetically
characterized Flavobacterium columnare strains in channel
catfish
Swapna Thomas and Andrew. E. Goodwin
A major disease of warm water fish is columnaris caused by the
bacterium Flavobacterium columnare. The disease causes
significant losses in the catfish and baitfish industries, but
little is known about the different strains of this bacterium and
their pathogenicity. Seventeen different isolates that formed the
characteristic flat, rhizoid, yellow pigmented colonies on Sheih
Agar and have the typical biochemical characteristics of F.
columnare were collected from several species of moribund fish
including Ictalurus punctatus, Notemigonus crysoleucas,
Pimephales promelas, Xiphophorus maculatus and Cyprinus
carpio. The bacteria are long, slender, Gram-negative rods and
exhibited length differences among isolates. The short isolates
varied from 1.5-3.0μm and the long isolates varied from 4.0-8.0μm
in length. The isolates varied in width from 0.45- 6.0μm. The DNA
sequence similarity of the isolates was analyzed by the Random
Amplification of Polymorphic DNA (RAPD) with five different
10-mers. The RAPD profile revealed the presence of different
strains among the isolates. Each strain produced a unique band
pattern and the isolates that showed identical band patterns with
the five primers were grouped as a single strain. The length
variation data together with the genetic data revealed the
presence of seven different strains among the isolates. The
channel catfish were challenged with the isolates of 5 x 109 F.
columnare/ ml. The variation in the pathogenicity of
high-virulence strains was analyzed using statistical tests. No
relationship was observed between the fish species origin of the
isolate and the pathogenicity in channel catfish in the challenge
studies.
- Channel catfish families resistant to ESC are different
from ESC susceptible families in both constitutive and inducible
complement activity.
Lazendra L. Hairston , Andrew E. Goodwin, and W.R. Wolters
Enteric septicemia (ESC) is one of the most important
diseases of channel catfish. The USDA-ARS Catfish Genetics
Research Unit is selectively breeding channel catfish for multiple
economically important traits including resistance to ESC. Bath
challenges of catfish reveal significant phenotypic variation in
mortality between families. These differences are consistent
whenever fish from the same families are challenged and
potentially controlled in part by genetic variation. In order to
discover which aspects of immune function are most important in
protection against ESC, replicate tanks with resistant and
susceptible catfish families were exposed to E. ictaluri.
Blood samples were collected before and 4-5 days post exposure.
Plasma complement activity was measured by exposing rabbit
erythrocytes to serial dilutions of catfish serum and measuring
changes in turbidity as blood cells were lysed. At 4-5 days
post-exposure, clinical signs of ESC were evident in sensitive and
resistant families. Mortality was greater in sensitive families,
typically 3 individuals in a 10 fish replicate (the fish were bled
and the experiment terminated prior to the time that massive
mortality would be expected). In pre-exposure samples, complement
activity was significantly higher in families resistant to ESC.
After E. ictaluri exposure, complement activity remained
the same in sensitive families, but was significantly elevated in
resistant families. While the actual importance of complement
activity related to ESC etiology is unknown, destruction of
bacterial cells by the complement system is a recognized component
of resistance to bacterial infection.
- Toxicity of aerially applied pesticides to fish and shrimp:
identification of compounds likely to cause mortality in
aquaculture
Kelly R.Winningham and Dr. Andrew E. Goodwin
Many warm water fish farms are located near crop production areas
where pesticides are applied by aerial application. There is a
widespread perception by farmers that pesticide drift is a major
source of fish losses, however much of the information needed to
evaluate the potential of pesticides to kill fish is not
available. Although LC50 data is available, it is not sufficient
because it does not include the most common aquacultural species
or life stages, and it does not provide information about safe
levels. In our work, we are testing 47 pesticides that were
selected based on their frequency of use, and their apparent risk
as determined by dividing the LC50 by the pesticide concentration
that would result if the pond received the “worst case” dosage of
chemical. Species studied include channel catfish, golden shiners,
largemouth bass, fat head minnows, and macrobranchium. The study
includes fry, fingerling, adult fish, and post-larval shrimp. The
experiments are conducted in static, clear water. Chemicals were
tested at their “worst case” concentration and those that produce
observable changes in fish behavior were further diluted to
determine their No Observable Effect Concentration (NOEC). Based
on research it has been shown that the calculated apparent risk
values are relevant in determining which chemicals pose a serious
potential risk to the aquaculture industry.
- Catfish anemia: new theories, no answers
Andrew E. Goodwin
Channel catfish suffer from a profound anemia that produces
hematocrits as low as 1%. Publications beginning in 1986 have
convincingly correlated catfish anemia with feed, variously
attributing the cause to fungal toxins, folic acid deficiency, or
feed contamination by pseudomonads or bacilli. However, anemia
typically occurs during the peak of the feeding season when the
time elapsed between feed manufacture and consumption is only 2-3
days. In addition, many ponds are fed from the same storage bins,
but only sporadic ponds on a farm will develop anemia.
Difficulties in applying feed-based theories to outbreaks of this
disease have led us to search for other causes of anemia. Our work
has involved five commercial catfish ponds that have a history of
fall outbreaks of anemia and 3 ponds on the same farm that have
not experienced anemia. Hematocrits were measured weekly from
August through October, algae samples were examined for
potentially toxic species, and fish were cultured for infectious
disease. No infectious agents or algae species were found to
correlate with anemia. On October 9, mean hematocrits dropped
precipitously from 28 to 17 percent in the anemia-prone ponds and
in all except one of the control ponds. Losses occurred in several
of the ponds during this period. Mean hematocrits returned to
normal values one week later. The precipitous nature of the
decline provides evidence that some cases of catfish anemia may
result from an acute hemolytic crisis.
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