Paraziti slatkovodnih riba
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RuthEllen Klinger and Ruth Francis Floyd
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Česta greška kod lečenja riba je pogrešna diagnoza
bolesti i lečenje pogrešnim lekovima ili hemikalijama. Kada te
hemikali ne deluju onda pokušavamo sa drugim lekovima itd... Upotreba
pogrešnog tretmana zbog pogrešne dijagnoze predstavlja bespotrebno
gubljenje vremena i novca i može biti pogubnije nego da nismo uopšte
lečili ribe. Većina ribljih parazita se može identifikovati samo
pomoću mikroskopa. Ako ne koristimo mikroskop, ili osoba koja ga
koristi nema predhodnog skustva, dijagnoza je otežana i diskutabilna.
Uspešni akvarista uči iskustvom. Početnici treba da nauče osnove
procedure za dijagnostiku i kako da koriste mikroskop da bi
identifikovali parazite.
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Paraziti sa kojima se najčešće susrećemo su
protozoe. Sa iskustvom, one se najlakše identifikuju, i obično se
najlakše i kontrolišu. Protozoe su jednoćelijski organizmi, jedni od
monogih koji žive slobodno plivajući u vodenoj sredini. Tipično,
ovim parazitima nije potreban prelazni domaćin da bi se
reprodukovali (direkni životni ciklus). Zbog toga, može se desiti da
ribe budu pokrivene ovim parayitima u voma velikom broju što izaziva
gubitak težine, otežano kretanje i smrt. Pet grupa protozoa je
opisano: ciliates, flagellates, myxozoans, microsporidians
i coccidians. Parazitske
protozoe u poslednje tri grupe je teško ili
čak nemoguće kontrolisati.
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Most of the protozoans identified by aquarists will be
ciliates. These organisms have tiny hair-like structures called cilia that are
used for locomotion and/or feeding. Ciliates have a direct life cycle and many
are common inhabitants of pond-reared fish. Most species do not seem to bother
host fish until numbers become excessive. In aquaria, which are usually closed
systems, ciliates should be eliminated. Uncontrollable or recurrent
infestations with ciliated protozoans are indicative of a husbandry problem.
Many of the parasites proliferate in organic debris accumulated in the bottom
of a tank or vat. Ciliates are easily transmitted from tank to tank by nets,
hoses, or caretakers' wet hands. Symptoms typical of ciliates include skin and
gill irritation displayed by flashing, rubbing, and rapid breathing.
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The disease called "Ich" or "white spot
disease" has been a problem to aquarists for generations. Fish infected with
this organism typically develop small blister-like raised lesions along the
body wall and/or fins. If the infection is restricted to the gills, no white
spots will be seen. The gills will appear swollen and be covered with thick
mucus. Identification of the parasite on the gills, skin, and/or fins is
necessary to conclude that fish has an "ich" infection. The mature parasite (
Figure 1 ) is very
large, up to 1000 m in diameter, is very dark in color due to the thick cilia
covering the entire cell, and moves with an amoeboid motion. Classically, I . multifiliis is identified by its large horseshoe-shaped
macronucleus. This feature is not always readily visible, however, and should
not be the sole criterion for identification. Immature forms of I . multifiliis are smaller and more translucent in appearance. Some
individuals have suggested that the immature forms of I . multifiliis resemble Tetrahymena . Fortunately, scanning the
preparation will usually reveal the presence of mature parasites and allow
confirmation of the diagnosis.
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Figure 1 .
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If only one
parasite is seen, the entire system should be treated immediately. "Ich" is an
obligate parasite and capable of causing massive mortality within a short
time. Because the encysted stage ( Figure 2 ) is resistant
to chemicals, a single treatment is not sufficient to treat "Ich". Repeating
the selected treatment ( Table 1 ) every other
day (at water temperatures 68--77°F) for three to five treatments will disrupt
the life cycle and control the outbreak. Daily cleaning of the tank or vat
helps to remove encysted forms from the environment. For more information, see
Extension Circular 920 , Ichythyophthirius multifiliis (White Spot) Infections of Fish .
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Figure 2 .
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Chilodonella is a ciliated
protozoan that causes infected fish to secrete excessive mucus. Infected fish
may flash and show similar signs of irritation. Many fish die when
infestations become moderate (five to nine organisms per low power field on
the microscope) to heavy (greater than ten organisms per low power field). Chilodonella is easily identified using a light microscope to examine
scrapings of skin mucus or gill filaments. It is a large, heart-shaped ciliate
(60 to 80 m) with bands of cilia along the long axis of the organism ( Figure 3 ). The organism
is easily recognized at 100X magnification. Chilodonella can be
controlled with any of the chemicals listed in Table 1 , and one
treatment is usually adequate. Chilodonella has been eliminated in
tanks using recirculating water systems by maintaining 0.02% salt solution.
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Figure 3 .
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Tetrahymena is a protozoan commonly
found living in organic debris at the bottom of an aquarium or vat. Tetrahymena is a teardrop-shaped ciliate ( Figure 4 ) that moves
along the outside of the host. The presence of Tetrahymena on the body
surface in low numbers (less than five organisms per low power field) is
probably not significant. It is commonly found on dead material and is
associated with high organic loads. Therefore, observing Tetrahymena on
fish, which have been on the tank bottom, does not imply the parasite is the
primary cause of death. One treatment of a chemical listed in Table 1 should be
adequate for control.
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Figure 4 .
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Identification
of Tetrahymena internally is a significant but untreatable problem. A
common site of internal infection is the eye. Affected fish will have one or
both eyes markedly enlarged (exophthalmia). Squash preparations made from
fresh material reveal large numbers (=> 10 per low power field) of Tetrahymena associated with fluids in the eye. Fish infected with Tetrahymena internally should be removed from the collection and
destroyed.
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Trichodina is one of the most
common ciliates present on the skin and gills of pond-reared fish. Low numbers
(less than five organisms per low power field) are not harmful, but when fish
are crowded or stressed, and water quality deteriorates, the parasite
multiplies rapidly and causes serious damage. Typically, heavily infested fish
do not eat well and lose condition. Weakened fish become susceptible to
opportunistic bacterial pathogens in the water. Trichodina can be
observed on scrapings of skin mucus, fin, or on gill filaments. Its erratic
darting movement and the presence of a circular, toothed disc within its body
( Figure 5 ) easily
identify it. Trichodina can be controlled with any of the treatments
from Table 1. One
application should be sufficient. Correction of environmental problems is
necessary for complete control.
Figure 5 .
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Ambiphyra , previously called Scyphidia , is a sedentary ciliate that is found on the skin, fins, or
gills of host fish. Its cylindrical shape, row of oral cilia, and middle bank
of cilia identify Ambiphyra ( Figure 6 ). It is common
on pond-reared fish, and when present in low numbers (less than five organisms
per low power field), it is not a problem. High organic loads and
deterioration of water quality are often associated with heavy, debilitating Ambiphyra infestations. This parasite can be controlled with one
application of any of the treatments listed in Table 1.
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Figure 6 .
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Apiosoma , formerly known as Glossatella , is another sedentary ciliate common on pond-reared fish. Apiosoma can cause disease if their numbers become excessive. The
organism can be found on gills, skin, or fins. The vase-like shape and oral
cilia are characteristic ( Figure 7 ). Apiosoma can be controlled with one application of one of the treatments from Table 1 .
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Figure 7 .
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Epistylis is a stalked ciliate that
attaches to the skin or fins of the host. Epistylis is of greater
concern than many of the ciliates because it is believed to secrete
proteolytic ("protein-eating") enzymes that create a wound, suitable for
bacterial invasion, at the attachment site. It is similar in appearance to Apiosoma except for the non-contractile long stalk ( Figure 8 ) and its
ability to form colonies. In contrast to the other ciliates discussed above,
the preferred treatment for Epistylis is salt. Fish can be placed into
a 0.02% salt solution as an indefinite bath, or a 3% salt dip. More than one
treatment may be required to control the problem. For more information, see
IFAS Extension Fact Sheet VM-85 , "Red
Sore Disease" in Game Fish .
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Figure 8 .
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Capriniana , historically called Trichophyra , is a sessile ciliate that attaches to the host's gills
with a sucker. They have characteristic cilia attached to an amorphous-shaped
body ( Figure 9 ). In
heavy infestations, Capriniana can cause respiratory distress in the
host. One treatment from a chemical listed in Table 1 should be
adequate.
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Figure 9 .
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Several chemicals commonly
used to control ciliated protozoans in freshwater fish are listed below for
your convenience. As stated above, most ciliate infestations respond to one
chemical treatment; however, fish that do not improve as expected should be
rechecked and retreated if necessary. Overtreatment with chemicals can cause
serious damage to fish. The reader is also highly encouraged to read Extension
Publication 673 (Mississippi State University), Calculation of Treatments, and IFAS Fact Sheet VM-78 , Bath
Treatments for Sick Fish .
Copper sulfate is an excellent compound for use in ponds to control
external parasites and algae; however, it is extremely toxic to fish. Its
killing action is directly proportional to the concentration of copper ions
(Cu ++ ) in the water. As the alkalinity of the water increases,
the concentration of copper ions in solution decreases. Consequently, a
therapeutic level of copper in water of high alkalinity would be lethal to
fish in water of low alkalinity. Conversely, a therapeutic concentration of
copper in water of low alkalinity would be insufficient to have the desired
action in water of higher alkalinity. For this reason, the alkalinity of
the water to be treated must be known in order to determine the amount of
copper sulfate needed. The amount of copper sulfate needed in mg/L is the
total alkalinity (in mg/L) divided by 100. For example, if the total
alkalinity in a pond is 100 mg/L, the concentration of copper sulfate needed
would be 100/100 or 1 mg/L. If you are unsure how to measure the alkalinity of
your water, or have never used copper sulfate, contact your aquaculture
Extension specialist for assistance. Never use copper sulfate in water that
has a total alkalinity less than 50 mg/L.
Because of its algicidal activity, copper sulfate can cause dangerous
oxygen depletions, particularly in warm weather. Emergency aeration should
always be available when copper sulfate is applied to your system or ponds.
Copper sulfate should not be run through the biofilter on a recirculation
system as it will kill the nitrifying bacteria. If possible, tanks should be
taken "off-line" during treatment with copper sulfate. If necessary, clean the
biofilter manually to decrease organic debris and residual parasite load. For
more information see IFAS Fact Sheet FA-13 , Use
of Copper in Aquaculture and Farm Ponds.
Potassium permanganate is effective against ciliates as well as fungus and
external columnaris bacteria, and it can be used in a pond or vat. Multiple
treatments with potassium permanganate are not recommended as it can burn
gills. Aeration should be available when potassium permanganate is used
because it is an algicide and can cause an oxygen depletion. Potassium
permanganate at the prescribed dosage (2 mg/L) does not seem to affect the
nitrifying bacteria in a biological filter; however, ammonia, nitrite, and pH
should be closely monitored following treatment. See also IFAS Fact Sheets FA-23 , The
Use of Potassium Permanganate in Fish Ponds, and FA-37 , Use
of Potassium Permanganate to Control External Infections of Ornamental Fish .
Formalin is an excellent parasiticide for use in small volumes of water
such as vats or aquaria. It is not recommended for pond use because it is a
strong algicide and chemically removes oxygen from the water. Vigorous
aeration should always be provided when formalin is used. See also IFAS Fact
Sheet VM-77 , Use of Formalin to Control Fish Parasites .
Used in proper amounts, salt effectively controls protozoans on the gills,
skin, and fins of fish. This is an effective treatment for small volumes of
water such as aquaria or tanks. Use in ponds as a treatment is generally not
recommended due to the large amount of salt and high cost of treatment that
would be needed to be effective. Salt should never be used on fish that
navigate by electrical field such as knifefish and elephant nose fish. See
also IFAS Fact Sheet VM-86 , The
Use of Salt in Aquaculture .
When using any treatment for fish, a bioassay (a test to determine safe
concentration) should be conducted on a few fish before large numbers of fish
are exposed. Fish species can react differently to various concentrations of
the chemical; therefore, fish undergoing treatment must be monitored closely
for adverse reactions. If the fish negatively react to treatment, the chemical
should be flushed immediately from the system, or the fish should be moved to
fresh water.
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Flagellated protozoans are small parasites that can
infect fish externally and internally. They are characterized by one or more
flagella that cause the parasite to move in a whip-like or jerky motion.
Because of their small size, their movement, observed at 200 or 400x
magnification under the microscope, usually identifies flagellates. Common
flagellates that infest fish are given below.
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Hexamita is a small (3 -- 18 m)
intestinal parasite commonly found in the intestinal tract of freshwater fish
( Figure 10 ). Sick
fish are extremely thin and the abdomen may be distended. The intestines may
contain a yellow mucoid (mucus-like) material. Recent taxonomic studies have
labeled the intestinal flagellate of freshwater angelfish as Spironucleus . Hexamita or Sprironucleus can be diagnosed by making a
squash preparation of the intestine and examining it at 200 or 400x
magnification. The flagellates can be seen where the mucosa (intestinal
lining) is broken. They move by spiraling and in heavy infestations, they will
be too numerous to be overlooked.
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Figure 10 .
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The recommended treatment for Hexamita / Spironucleus is
metronidazole (Flagyl). Metronidazole can be administered in a bath at a
concentration of 5 mg/L (18.9 mg/gallon) every other day for three
treatments. Medicated feed is even more effective at a dosage of 50
mg/kg body weight (or 10 mg/gm food) for five consecutive days. See also IFAS Fact Sheet VM-67 , Management of Hexamita in Ornamental Cichlids .
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Ichthyobodo , formerly known as Costia , is a commonly encountered external flagellate ( Figure 11 ). Ichthyobodo- infected fish secrete copious amounts of mucus. Mucus
secretion is so heavy that catfish farmers popularly refer to the disease as
"blue slime disease". Infected angelfish also produce excessive mucus that can
give dark colored fish a gray or blue coloration along the dorsal body wall.
Infected fish flash and lose condition, often characterized by a thin,
unthrifty appearance. Ichthyobodo can be located on the gills, skin,
and fins, however, it is difficult to identify because of its small size. The
easiest way to identify Ichthyobodo is by its corkscrew swimming
pattern. With a good microscope, the attached organism can be seen at 400x
magnification. The organism is easily controlled using one application of one
of the treatments listed in Table 1.
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Figure 11 .
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Piscinoodinium is a sedentary
flagellate that attaches to the skin, fin, and gills of fish. The common name
for Piscinoodinium infection is "Gold Dust" or "Velvet" Disease. The
parasite has an amber pigment, visible on heavily infected fish. Affected fish
will flash, go off feed, and die. Piscinoodinium is most pathogenic to
young fish. The life cycle of this parasite can be completed in 10--14 days at
73--77°F ( Figure12 ),
but lower temperatures can slow the life cycle. Also, the cyst stage is highly
resistant to chemical treatment. Therefore, several applications of a
treatment ( Table 1
) may be necessary to eliminate the parasite. For non-food species,
chloroquin (10mg/L prolonged bath) has been reported to be efficacious. For
more information, see IFAS Fact Sheet VM-90 , Amyloodinium Infections of Marine Fish , the marine counterpart to Piscinoodinium .
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Figure12 .
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Cryptobia is a flagellated
protozoan common in cichlids. They are often mistaken for Hexamita as
they are similar in appearance. However, Cryptobia are more
drop-shaped, with two flagella, one on each end. Also, Cryptobia "wiggles" in a dart-like manner, whereas Hexamita "spirals". Cryptobia typically is associated with granulomas ( Figure 13 ), in which
the fish "walls off" the parasite. These parasites have been observed
primarily in the stomach, but may be present in other organs. Fish afflicted
with Cryptobia may become thin, lethargic and develop a dark skin
pigmentation. A variety of treatments are presently being studied with limited
success. Nutritional management has proven to take an active role in its
control.
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Figure 13 .
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Myxozoa are parasites that are widely dispersed in native and
pond-reared fish populations. Most infections in fish create minimal problems,
but heavy infestations can become serious, especially in young fish. Myxozoans
are parasites affecting a wide range of tissues. They are an extremely
abundant and diverse group of organisms, speciated by spore shape and size.
Spores can be observed in squash preparations of the affected area at 200 or
400x magnification or by histologic sections.
Clinical signs vary, depending on the target organ. For example, fish may
have excess mucus production, observed with Henneguya ( Figure 14 ) infections.
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Figure 14 .
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White or
yellowish nodules may appear on target organs. Chronic wasting disease is
common among intestinal myxozoans such as with Chloromyxum . "Whirling
disease" caused by Myxobolus cerebralis has been a serious problem in
salmonid culture. Elimination of the affected fish and disinfection of the
environment is the best control of myxozoans. There are no established
remedies for fish. Spores can survive over a year, so disinfection is
mandatory for eradication. See IFAS Fact Sheet VM-87 , Sanitation Practices for Aquaculture Facilities .
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Microsporidians are intracellular parasites that
require host tissue for reproduction. Fish acquire the parasite by ingesting
infective spores from infected fish or food. Replication within spores
(schizogony) causes enlargement of host cells (hypertrophy). Infected fish may
develop small tumor-like masses in various tissues. Diagnosis is confirmed by
finding spores in affected tissues, either in wet mount preparations, or in
histologic sections.
Clinical signs depend on the tissue infected and can range from no visible
lesions to mortalities. In the most serious cases, cysts enlarge to a point
that organ function is impaired and severe morbidity and/or mortality results.
A common microsporidian infection is Pleistophora , which infects
skeletal muscle ( Figure15 ).
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Figure15 .
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There is no
treatment for microsporidian infections in fish. Spores are highly resistant
to environmental conditions and can survive for long periods. Elimination of
the infected stock and disinfection of the environment is recommended.
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Coccidia are intracellular
parasites described in a variety of wild-caught and cultured fish ( Figure 16 ). Their role
in the disease process is poorly understood, but there is increasing evidence
that they are potential pathogens. The most common species encountered in fish
are intestinal infections. Inflammation and death of the tissue can occur,
which can affect organ function. Other infection sites include reproductive
organs, liver, spleen, and swim bladder.
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Figure 16 .
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Clinical signs
depend on target organ affected but may include general malaise, poor
reproductive capacity, and chronic weight loss. A definitive diagnosis of
tissue coccidia should be completed with histologic or electron microscopy.
Several compounds have been used to control coccidiosis with some success;
however, consultation with an experienced fish health professional is
recommended. Maintaining a proper environment and reducing stress appear to be
important in preventing coccidia outbreaks in cultured fish.
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MONOGENEAN TREMATODES Monogenean trematodes, also called flatworms or
flukes, commonly invade the gills, skin, and fins of fish. Monogeneans have a
direct life cycle (no intermediate host) and are host- and site-specific. In
fact, some adults will remain permanently attached to a single site on the
host.
Freshwater fish infested with skin-inhabiting flukes become lethargic, swim
near the surface, seek the sides of the pool or pond, and their appetite
dwindles. They may be seen rubbing the bottom or sides of the holding facility
(flashing). The skin where the flukes are attached shows areas of scale loss
and may ooze a pinkish fluid. Gills may be swollen and pale, respiration rate
may be increased, and fish will be less tolerant of low oxygen conditions.
"Piping", gulping air at the water surface, may be observed in severe
respiratory distress. Large numbers (>10 organisms per low power field) of
monogeneans on either the skin or gills may result in significant damage and
mortality. Secondary infection by bacteria and fungus is common on tissue with
monogenean damage.
Gyrodactylus and Dactylogyrus are the two most common genera
of monogeneans that infect freshwater fish ( Figure 17 ). They differ
in their reproductive strategies and their method of attachment to the host
fish. Gyrodactylus have no eyespots, two pairs of anchor hooks, and are
generally found on the skin and fins of fish. They are live bearers
(viviparous) in which the adult parasite can be seen with a fully developed
embryo inside the adult's reproductive tract. This reproductive strategy
allows populations of Gyrodactylus to multiply quickly, particularly in
closed systems where water exchange is minimal.
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Figure 17 .
| Dactylogyrus prefers to
attach to gills. They have two to four eyespots, one pair of large anchor
hooks, and are egg layers. The eggs hatch into free-swimming larvae and are
carried to a new host by water currents and their own ciliated movement. The
eggs can be resilient to chemical treatment, and multiple applications of a
treatment are usually recommended to control this group of organisms.
Treatment of monogeneans is usually not satisfactory unless the primary
cause of increased fluke infestations is found and alleviated. The treatment
of choice for freshwater fish is formalin, administered as a short-term or
prolonged bath ( Table 1
). Fish that are sick do not tolerate formalin well, so they need to be
carefully monitored during treatment. Potassium permanganate can also be
effective in controlling monogeneans. For more information, see IFAS Fact
Sheet FA-28 , Monogenean Trematodes .
DIGENEAN TREMATODES Digenean trematodes have a complex life cycle
involving a series of hosts (Figure 18 ). Fish can be
the primary or intermediate host depending on the digenean species. They are
found externally or internally, in any organ. For the majority of digenean
trematodes, pathogenicity to the host is limited.
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(Figure 18 . | The life
stage most commonly observed in fish is the metacercaria, which encysts in
fish tissues ( Figure 19
). Again, metacercaria that live in fish rarely cause major problems.
However, in the ornamental fish industry, digenetic trematodes from the family
Heterophyidae, have been responsible for substantial mortalities in
pond-raised fish. These digeneans become encysted into gill tissue and
respiratory distress is eminent.
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Figure 19 . | Another
example of a metacercaria that could cause problems in cultured fish is the
genus Posthodiplostonum or the white grub. This has caused mortalities
in baitfish, but usually the only negative effect is reduced growth rate, even
when the infection rate is high. In cases where mortalities occur, there are
unusually high numbers in the eye, head, and throughout the visceral organs.
Another fluke is Clinostonum , often called yellow grub. It is a
large trematode and although it does not cause any major problems for fish, it
is readily seen and will make fish unmarketable for aesthetic reasons.
The best control of digenean trematodes is to break the life cycle of the
parasite. Elimination of the first intermediate host, the freshwater snail is
often recommended. Copper sulfate in ponds has been used with limited success
and is most effective against snails when applied at night, due to their
nocturnal feeding activity. For Florida ornamental fish growers a chemical for
snail control, Bayluscide, is available. This is a Restricted Use Pesticide
and access to it is controlled. For more information, contact your aquaculture
Extension specialist or the University of Florida Tropical Aquaculture
Laboratory in Ruskin, Florida.
NEMATODES Nematodes, also called roundworms, occur worldwide in all
animals. They can infect all organs of the host, causing loss of function of
the damaged area. Signs of nematodiasis include anemia, emaciation,
unthriftiness and reduced vitality. Three common nematodes affecting fish are
described.
<italics><string>Camillanus
</string></italics> Camillanus is easily recognized as
a small thread-like worm protruding from the anus of the fish. Control of this
nematode in non-food fish is with fenbendazole, a common antihelminthic.
Fenbendazole can be mixed with fish food (using gelatin as a binder) at a rate
of 0.25% for treatment. It should be fed for three days, and repeated in three
weeks.
<italics><string>Capillaria
</string></italics> Capillaria is a large roundworm
commonly found in the gut of angelfish ( Figure 20 ), often
recognized by its double operculated eggs in the female worm ( Figure 21 ). Heavy
infestations are associated with debilitated fish, but a few worms per fish
may be benign. Fenbendazole is recommended for treatment (see above).
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Figure 20 . |
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Figure 21 . |
<italics><string>Eustrongylides
</string></italics> Eustrongylides is a nematode that
uses fish as its intermediate host. The definitive host is a wading bird, a
common visitor to ponds. The worm encysts in the peritoneum or muscle of the
fish and appears to cause little damage. Because of the large size of the
worms ( Figure 22 ),
infected fish may appear unsuitable for retail sales. Protecting fish from
wading birds and eliminating the intermediate host, the oligocheate or Tubifex
(soft-bodied worms), are the best means to prevent infection.
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Figure 22 . |
CESTODES Cestodes, also called tapeworms, are found in a wide variety
of animals, including fish ( Figure 23 ). The life
cycle of cestodes is extremely varied with fish used as the primary or
intermediate host. Cestodes infect the alimentary tract, muscle or other
internal organs. Larval cestodes called plerocercoids are some of the most
damaging parasites to freshwater fish. Plerocercoids decrease carcass value if
present in muscle, and impair reproduction when they infect gonadal tissue.
Problems also occur when the cestode damages vital organs such as the brain,
eye or heart.
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Figure 23 . | One of the
most serious adult cestodes that affect fish is the Asian tapeworm, Bothriocephalus acheilognathi . It has been introduced to the
United States with grass carp and has caused serious problems with bait minnow
producers.
Praziquantel at 2 -- 10 mg/L for 1 to 3 hours in a bath is effective in
treating adult cestode infections in ornamental fish. At this time, there is
no treatment that can be used for food fish. Also, there is no successful
treatment for plerocercoids. Ponds can be disinfected to eradicate the
intermediate host, the copepod.
PARASITIC CRUSTACEA Parasitic crustacea are increasingly serious
problems in cultured fish and can impact wild populations. Most parasitic
crustacea of freshwater fish can be seen with the naked eye as they attach to
the gills, body and fins of the host. Three major genera are discussed below.
<italics><string>Ergasilus
</string></italics> Ergasilus ( Figure 24 ) are often
incidental findings on wild or pond-raised fish and probably cause few
problems in small numbers. However, their feeding activity causes severe focal
damage and heavy infestations can be debilitating. Most affect the gills of
freshwater fish, commonly seen in warm weather. A 3% salt dip, followed by 0.2
%-prolonged bath for three weeks, may be effective in eliminating this
parasite.
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Figure 24 . |
<italics><string>Lernaea
</string></italics> Lernaea , also known as anchor worm
( Figure 25 ), is a
common parasite of goldfish and koi, especially during the summer months. The
copepod attaches to the fish, mates, and the male dies. The female then
penetrates under the skin of the fish and differentiates into an adult. Heavy
infections lead to debilitation and secondary bacterial or fungal infections.
Removal of the parasite by hand with forceps may control lernaeid infestations
with careful monitoring of the wound. A 3% salt dip followed by 0.2%-prolonged
immersion has been used to effectively control Lernaea in goldfish and
koi ponds.
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Figure 25 . |
<italics><string>Argulus
</string></italics> Argulus or fish louse is a large
parasite ( Figure 26
) that attaches to the external surface of the host and can be easily seen
with the unaided eye. Argulus is uncommon in freshwater aquarium fish
but may occur if wild or pond-raised fish are introduced into the tank. It is
especially common on goldfish and koi.
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Figure 26 . | Individual
parasites can be removed from fish with forceps, but this does not eliminate
parasites in the environment. A prolonged immersion of 0.02 - 0.2% salt may
control re-infection to the fish host.
LEECHES Leeches are occasionally seen in wild and pond-raised fish.
They have a direct life cycle with immature and mature worms being parasitic
on host's blood. Pathogenesis varies with number and size of worms and
duration of feeding. Heavily infested fish often have chronic anemia. Fish may
develop secondary bacterial and fungal infections at the attachment site.
Leeches resemble trematodes but are much larger and have anterior and
posterior suckers ( Figure 27 ). Dips in 3%
saltwater are effective in controlling leeches. Ponds with heavy leech
infestation require drainage, treatment with chlorinated lime, followed by
several weeks of drying. This will destroy the adults and their cocoons
containing eggs.
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Figure 27 . |
CONCLUSION Most fish health problems occur because of environmental
problems: poor water quality, crowding, dietary deficiencies, or "stress". The
best cure for any fish health problem is prevention. Good water quality
management and proper fish husbandry techniques will eliminate most parasites
described here. Information concerning basic fish culture, pond management,
water quality, and economics is available in aquaculture extension circulars
from your Cooperative Extension Service agent.
ACKNOWLEDGMENTS The authors wish to especially thank Chris Tilghman
and Peggy Reed for their artistic contributions to this circular, and Roy
Yanong for the photo of Coccidia .
Tables Table 1.
Table 1. Chemical treatments for
the control of external ciliates. "X" indicates that the chemical should
not be used for this type of treatment.
|
Chemical
|
Dip
|
Short-term Bath
|
Prolonged (indefinite) Immersion
|
Copper sulfate
|
X
|
X
|
total alkalinity/100 (up to 2.5 mg/L), Do
not use if total alkalinity < 50mg/L
|
|
|
|
|
|
|
Potassium permanganate
|
X
|
10 mg/L, 30 min
|
2 mg/L
|
Formalin
|
X
|
150--250 mg/L, 30 min
|
15--25 mg/L (2 drops/gallon or 1 mL/10
gallons)
|
|
|
|
Salt
|
3%, Duration is species dependent.
|
1%, 30 min to 1 hr, species dependent
|
0.02--0.2%
|
|
|
Footnotes 1. This document is
Circular 716, one of a series of the Department of Fisheries and Aquatic
Science, Florida Cooperative Extension Service, Institute of Food and
Agricultural Sciences, University of Florida. First published March 1987 by
Frederick J. Aldridge and Jerome V. Shireman; Reprinted April 1994; Revised
December 1998. Please visit the EDIS Web site at
http://edis.ifas.ufl.edu.
2. RuthEllen Klinger, biological
scientist, Department of Large Animal Clinical Sciences (College of Veterinary
Medicine) and Ruth Francis Floyd, associate professor, Department of Fisheries
and Aquatic Sciences (Institute of Food and Agricultural Sciences), Department
of Large Animal Clinical Sciences (College of Veterinary Medicine),
Cooperative Extension Service, Institute of Food and Agricultural Sciences,
University of Florida, Gainesville, 32611.
The Institute of Food and Agricultural Sciences is an equal
opportunity/affirmative action employer authorized to provide research,
educational information and other services only to individuals and
institutions that function without regard to race color, sex, age, handicap,
or national origin. For information on obtaining other extension publications,
contact your county Cooperative Extension Service office.
Florida
Cooperative Extension Service / Institute of Food and Agricultural Sciences /
University of Florida / Christine Taylor Waddill, Dean
Copyright Information This document is copyrighted by the University
of Florida, Institute of Food and Agricultural Sciences (UF/IFAS) for the
people of the State of Florida. UF/IFAS retains all rights under all
conventions, but permits free reproduction by all agents and offices of the
Cooperative Extension Service and the people of the State of Florida.
Permission is granted to others to use these materials in part or in full for
educational purposes, provided that full credit is given to the UF/IFAS,
citing the publication, its source, and date of publication.
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