Parasitic Copepod (Achtheres ssp.) Affect Striped Bass
The copepod (Achtheres ssp.), sometimes called gillmaggots, have infested populations of striped bass and resulted in severe fish kills and has been identified in Lake Ouachita in Arkansas.
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Where the the kills of Striped Bass occurred it was
directly linked to stress and infestation of the parasite. Achtheres should
not cause significant harm to healthy fish. However, heavy infestations could
lead to secondary bacterial and fungal infections in fish already
compromised by poor water quality or poor condition. These secondary
infections could lead to a limited amount of fish mortality.
Smith Mountain Lake in Virginia has been the hardest hit by the parasite and
most of the trophy striped bass were killed in 2003. The Virginia natural
resources agency gives out certificates to anglers who catch striped bass
over 20 lbs, and up until 2003 they gave out an average of 150 certificates.
After the kill in 2003, this number had dropped to an average of seven
certificates in 2003 and 2004.
The kill in Smith Mountain Lake occurred in the
winter and spring of 2003, after a large-scale threadfin shad kill in
winter. The fish affected by the parasite were in poor condition due to lack
of forage.
Another kill occurred on Norris Lake, TN and the parasite was found in large
numbers on dead striped bass. Once again, abnormally warm water temperatures
that were caused by high flows stressed the striped bass population.
The Copepod parasite has only caused fish kills when some type of
stressor is involved.
Where has the copepod been found?
The parasite has been found in the following reservoirs and
watersheds in Virginia, North Carolina, Tennessee, Virginia, North
Carolina and Arkansas.
1981 - Tellico Reservoir, TN - largemouth bass
2000 - Watts Barr Reservoir, TN - striped bass
2000 -Tim’s Ford Reservoir, TN - striped bass
2001 - Melton Hill Reservoir, TN - striped bass
2001 - Watauga Reservoir, TN - 1 smallmouth bass
2002 - Old Hickory Reservoir, TN - striped bass
2002 - Norris Reservoir, TN - striped bass
2002 - Smith Mountain Lake, VA - striped bass
2003 - Kerr Reservoir, VA - striped bass
2003 - Leesville Resrvoir, VA - striped bass
2004 - Lake Norman, NC - striped bass
2004 - Gaston Reservoir, NC - striped bass
2004 -Tellico Reservoir, TN - 1 striped bass
2004 - Smith Mountain Lake, VA - largemouth
2004 - Cherokee Reservoir, TN - black bass
2005 - Cherokee Reservoir, TN - white bass (angler report)
2006 -
Ouachita Lake, AR - striped bass
2006 - Fort Patrick Henry Reservoir, TN - striped bass (angler report)
2006 - Hiwassee River, TN - striped bass (angler report)
2007 - Cherokee Reservoir, TN - striped and hybrid striped bass
Where did the parasite come from?
Evidence gathered from kills in Virginia and North Carolina suggest that the
parasite in fairly new to these areas. Previous research on the parasite in
Europe showed that a heavily infested fish would have 7-8 copepods inside
the mouth. It was also shown that approximately 30% of the population
was infested with the parasite. A few striped bass collected in Smith
Mountain Lake had over 400 parasites attached inside the mouth and every
fish that biologists have captured in the past two years has had some level
of infestation (incidence rate of 100%). This evidence suggests that the
striped bass in Smith Mountain Lake may be naïve to the parasite and are
heavily infested.
Dan Wilson (VA) has shown that the striped bass parasite showed up in the
headwaters of the Roanoke River and has eventually moved down the river
system into bordering waters of North Carolina. This suggests that the
parasite is spreading throughout the system and may have been introduced.
Others believe the parasite has been around for a long time and conditions
are right for it to cause fish kills. These fish kills have put the parasite
on the map.
Other species can carry the Copepod parasite.
The parasite has been found on a variety of fish, but fish kills have only
occurred in striped bass populations. Biologists from Tennessee have found
the copepod in small numbers on largemouth and smallmouth bass.
Identification and life cycle of the parasite.
The copepod is easily identified in its adult life stage and can be found
inside the mouth of adult striped, largemouth and smallmouth bass. The
parasite will attach to the gill cartilage, mouth and tongue. Two large egg
sacks are indicative of adult females attached in the mouth.
The life cycle of this copepod is similar to other species of parasites,
where sub-adult life stages can be found on the gill filaments. These life
stages mature and migrate to the inside of the mouth to release eggs and
infest other striped bass.
Treatments options.
Anecdotal evidence has shown that high concentrations of salt can
effectively control the parasite. Employees for a large aquarium in Virginia
have eliminated the copepod from striped bass by switching from freshwater
(salinity 1-5 ppt) to saltwater (20-25 ppt salinity).
Good news.
Thankfully, the parasite does not cause fish kills in every lake where fish
have been found to harbor the pathogen. The copepod has been found in the
following lakes in Tennessee, but no striped bass kills have occurred:
Watts Bar, Tims Ford, Old Hickory, Tellico, Melton Hill, and Cherokee. All
kills took place when striped bass were exposed to stressful conditions
(high water temperature and limited forage).
Parasite did not seem to affect smaller fish (up to 1 ½ years of
age—20-24”).
Kills have subsided and there have been no repeat kills.
Lake Ouachita
striped bass have the copepod.
According to Arkansas Game and Fish Commission biologist Brett Hobbs, who
recently conducted gill-netting samples on Lake Ouachita near Mt. Ida,
biologists observed the parasitic copepods, Achtheres, in the mouth and gill
raker area of striped bass. "All stripers in the netting sample did have
some of the parasites. Thus far we classify the infestation as light to
moderate although it may get worse before it gets better," Hobbs said.
Copepod (Achtheres ssp.)
Tennessee Wildlife Resources Agency reports several species of parasitic
copepods can inflict great harm and even kill fish, but Ahctheres is not
considered to be one of them. Virginia Department of Game and Inland
Fisheries reported Achtheres contributed to a striped bass die-off in Smith
Mountain Lake. They reported the stripers were in poor shape due to reduced
shad forage in the lake and large stripers collected from the die-off had
high numbers of Achtheres, Hobbs explained.
"This parasitic copepod is visible as the adult stage in the mouth of the
host fish. The adult stage is about 2 to 3 millimeters long and creamy to
white-yellow colored. For you anglers out there, they are shaped like an
Uncle Josh pork frog (body with split tail)," Hobbs stated. "The tail
portion of the copepod is actually egg sacs which will distribute into the
water and hatch into a larval free-swimming form which will infect other
fish," he added.
A leading researcher, Dr. Thomas Shahady from Lynchburg College in Virginia,
has ongoing research which is testing the effect of this parasite on the
respiration of the host fish. Early study results indicate the parasites
increase respiration rate which could be most problematic during low
dissolved oxygen periods, Hobbs said. "The bad news is this parasite
persists in affected lakes for at least several years after infestation, but
typically in lower numbers. We will have to wait for further research
findings to determine how harmful this parasite will be to our fisheries,"
Hobbs said.
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