Pandey et al. UJP 2013, 02 (02): Page 1-3
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Universal Journal of Pharmacy
Review Article
ISSN 2320-303X
Take Research to New Heights
TREATMENT FOR CERTAIN PARASITIC DISEASES OF FISHES
Pandey Govind*
*
Professor/Principal Scientist & In-Charge,
Department of Veterinary Pharmacology & Toxicology, College of Veterinary Science & Animal Husbandry, Rewa
The Nanaji Deshmukh Veterinary Science University (NDVSU), Jabalpur, MP, India
Received 26-02-2013; Revised 10-03-2013; Accepted 12-04-2013
ABSTRACT
The parasitic infection may cause severe morbidity and mortality in fish. For example, the flagellates of the
“Hexamita” parasite are often associated with high mortality in fish. The flagellate parasites interfere with nutrition
by competing for essential nutrients and/or by damaging the intestinal epithelium. The ‘hexamitosis’ is probably the
most frequent internal flagellate parasitosis of fish, notably in the young salmonids. The H. salmonis infected fish pass
both trophozoites and cysts in faeces. Several drugs have been investigated for the treatment of parasite infection in
different species of fish. However, the only oral pharmacological treatment of H. salmonis determined to date have
been the drugs of nitroimidazole group, which show the activity against different protozoan groups, including
flagellates and ciliates. The current treatment of choice is dimetridazole or metronidazole in the feed. The H. salmonis
infection in the rainbow trout (Oncorhynchus mykiss) fish was completely eradicated not only by the metronidazole,
but also by benznidazole, ronidazole and secnidazole. The four nitroimidazoles, e.g., albendazole, aminosidine,
diethylcarbamazine and nitroscanate completely eliminated the parasite infection in the fish. Three drugs have been
also been recommended for the treatment of protozoan parasitoses of fish, viz., amprolium, bithionol and toltrazuril.
Among these three (amprolium, bithionol and toltrazuril), amprolium was found to be effective after oral
administration; indeed, its administration by this route is recommended for myxosporidiosis. Bithionol and toltrazuril
have been effective only in the bath treatments.
Keywords: Disease, Antiparasitic Drugs, Fish, Parasites, Treatment.
INTRODUCTION
The intestinal infection of fish by many parasites can
cause severe morbidity and mortality. For instance, the
flagellates of the Hexamita parasite are often
associated with high mortality in fish. Some workers
have suggested that the pathological effects arise when
the host is weakened by other factors like inadequate
diet, change in diet, low oxygen content in the water,
overcrowding, inappropriate handling and/or keeping
fish of different sizes together1. It has been suggested
that the flagellate parasites interfere with nutrition by
competing for essential nutrients and/or by damaging
the intestinal epithelium2. In both salmonids and
tropical aquarium fish, the intestinal parasitoses are
*Corresponding author:
Dr. Govind Pandey
Professor/Principal Scientist & In-Charge,
Deptt. of Veterinary Pharmacology & Toxicology,
College of Veterinary Science & AH, Rewa
(NDVSU, Jabalpur), MP.
E-mail: drgovindpandey@rediffmail.com
often pathogenic only when the number of parasites
present is very high3.
The hexamitosis is probably the most frequent internal
flagellate parasitosis of fish, notably in the young
salmonids, though also in carp, aquarium species and
various marine fish. Heavily infected fish are weak,
listless, anorexic and emaciated, so that the head of a
particular fish appears large with respect to the body
(‘pinhead fish’). The affected fish typically swim on
their side, or with corkscrew movements. Populations
affected by the acute hexamitosis show high mortality
over a very short period, due to rapid multiplication of
the parasite and associated damage to the intestinal
epithelium. The chronic form of hexamitosis is likewise
common, and generally occurs between spring and
autumn; mortality per unit time is only slightly higher
than in healthy fish, but severe losses may occur
because the situation continues for a period of weeks 4.
In trout and other salmonid fish infected with Hexamita
salmonis parasite, the adverse effects commonly
observed are anaemia, weight loss5, dark coloration,
enteritis, excessive body mucus and yellowish intestinal
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Pandey et al. UJP 2013, 02 (02): Page 1-3
mucus (attributable to modified release of bile into the
digestive
tract).
In
addition,
the
intestinal
haemorrhage and liver cell necrosis may also be
observed3. It is worth noting that the H. salmonis
infected fish pass both trophozoites and cysts in
faeces4. The fish that appear to be heavily infected
(i.e., numerous parasites in the pyloric caecae and the
intestine) may show no signs of damage to the mucosa,
and no evidence of invasion of the epithelium by the
parasite. Cysts were not observed at any stage, even
after subjecting samples to concentration methods
such as the Bailinger method. Cysts thus appear to be
very rare6.
Several drugs have been investigated for the treatment
of parasite infection in different species of fish.
However, the only oral pharmacological treatment of
H. salmonis determined to date have been the drugs of
nitroimidazole group7-8, which show the activity against
different protozoan groups, including flagellates and
ciliates. Therefore, the current treatment of choice is
dimetridazole or metronidazole in the feed3-4,9.
Further, there have been few studies of the possible
anti-Hexamita or antiparasitic effect of the drugs of
other groups. Treatment for ectoparasitic diseases in
freshwater fish with formalin seems at present to be
ineffective. Formalin possibly leaves toxic residues in
fish flesh and in the environment which are eventually
harmful to the consumers. The alternative way to solve
this problem is to use traditional medicinal plants
instead10. The treatment with medicinal plants having
antibacterial activity is a potentially beneficial
alternative in the aquaculture. These herbs mitigate
many of the side effects which are associated with
synthetic antimicrobials. Additionally, the plantderived phytomedicines provide a cheaper source for
treatment and greater accuracy than chemotherapeutic
agents. Recently, research has been initiated to
evaluate the feasibility of herbal drugs in fish
diseases11-12.
In view of the above facts, the present article
elucidates regarding some of the antiparasitic drugs
which have been cited for the treatment of certain
parasitic diseases of the fish.
Some Antiparasitic Drugs against Fish Parasites:
The results a study6 confirm the efficacy of
nitroimidazoles against the parasitic diseases of fish. In
this study, the H. salmonis infection in the rainbow
trout (Oncorhynchus mykiss) fish was completely
eradicated not only by the metronidazole (which has
been recommended earlier for the treatment of
hexamtosis), but also by benznidazole, ronidazole and
secnidazole (which have not been assayed previously).
The non-nitroimidazoles, e.g. albendazole, amnosidine,
diethethylcarbamazine
and
nitroscanate
also
completely eliminated the infection. The remaining
non-nitroimidazoles tested (amprolium, bithionol,
febantel,
flubendazole,
levamisole,
netobimin,
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niclosamide, nitroxynil, oxibendazole, parbendazole,
piperazine, praziquentel, tetramisole, thiophanate,
toltrazuril, trichlorfon and triclabendazole) were found
not effective. The four nitroimidazoles (albendazole,
aminosidine,
diethylcarbamazine,
nitroscanate)
completely eliminated the infection @ 5 g/kg feed for 2
days 4. All nitroimidazoles except metronidazole were
effective even at the lower dose of 2 g/kg feed for 2
days. These results confirm the efficacy of these drugs
when administered for a shorter period and at much
lower doses than the other drugs tested. The only nonnitroimidazole drugs that completely eliminated
infection were albendazole, aminosidine, diethyl
carbamazine and nitroscanate. Out of albendazole,
aminosidine, diethylcarbamazine and nitroscanate
antiparasitic drugs, the only one previously
recommended for the treatment of infection by H.
salmonis is aminosidine (15 g/kg feed for 3 consecutive
days)13. Nitroscanate appears to have a rather broad
activity spectrum, since it has been shown to be
effective for bath treatment of Gyrodactylus14. Neither
albendazole nor diethylcarbamazine has previously
been shown to be effective for treatment of protozoan
parasitoses of fishes. None of the antiparasitic drugs,
viz., albendazole, aminosidine, diethylcarbamazine and
nitroscanate showed the negative effects (signs of
toxicity, behavioural effects, including anomalous
swimming movements, rejection of food), suggesting
that all four nitroimidazoles are viable options for the
treatment of infection of salmonids by H. salmonis.
This is of particular interest in view of the fact that H.
salmonis strains apparently resistant to metronidazole
have recently appeared on some farms6.
Three drugs have been also been recommended for the
treatment of protozoan parasitoses of fish, viz.,
amprolium8-9,13, bithionol6 and toltrazuril8-9,15. Of these,
toltrazuril has been most widely used for the treatment
of parasitoses of fish, and indeed this drug has been
recommended for the treatment of various
microsporidian and myxosporidian infections 15. This
drug is not, however, effective for the treatment of
infestation by the ectoparasitic ciliate Ichthyophthirius
multifilils16. Among the amprolium, bithionol and
toltrazuril, amprolium was found to be effective after
oral administration; indeed, its administration by this
route is recommended for myxosporidiosis. Bithionol
and toltrazuril have been shown to be effective only in
bath treatments. In a study of efficacy for the
treatment of infestation by the flagellate Ichthyobodo
necator, complete elimination of infestation in all fish
assayed was achieved after bathing with bithionol at
25g 1-1 for 3 hr on 2 consecutive days, but not after
bathing with amprolium or toltrazuril17.
Nitroimidazoles are currently the only drugs
recommended for oral treatment of H. salmonis
infection.
Earlier
reports
have
recommended
dimetndazole at the dose of 1.5 g/kg feed for 3 days13,
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Pandey et al. UJP 2013, 02 (02): Page 1-3
or at 15 g/kg feed for 4 to 7 days 8. Metronidazole has
been recommended at doses of 0.5 mg/kg feed for 2
days7, 20 mg per/kg feed for 2 days4, or 1.5 g per/kg
feed for 3 days. Bath treatment with metronidazole has
been recommended for infections with Trichodina,
Ambiphyra and Chilodonella6.
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7.
8.
CONCLUSION
Severe morbidity and mortality have been noticed by
the parasitic infection in fish. The ‘hexamitosis’
(caused by H. salmonis parasite) is probably the most
frequent internal flagellate parasitosis of fish,
particularly in the young salmonids. The H. salmonis
infected fish pass both trophozoites and cysts in faeces.
The oral treatment of this parasite can be done with
the nitroimidazole group, which shows the activity
against
different
protozoan
groups,
including
flagellates and ciliates. Presently, the treatment of
parasitic infection in fish can be done by dimetridazole
or metronidazole given with feed. The nitroimidazoles,
e.g., albendazole, aminosidine, diethylcarbamazine
and nitroscanate can completely eliminate the parasite
infection in the fish. Three drugs, viz., amprolium,
bithionol and toltrazuril have been also been
recommended for the treatment of protozoan
parasitoses of fish.
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Source of support: Nil, Conflict of interest: None Declared
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