Caused By Different Parasites In Fishes And Their Preventive
Maqsood*, Prabjeet Singh, Munir Hassan Samoon, Gohar Bilal Wani and
of Fisheries, Sher-e-Kashmir University of Agricultural Science and
*Corresponding author E-mail : firstname.lastname@example.org.
is probably the most common parasite of all fishes. The
common name for this parasite and disease is "Ich" or "white
spot". The mature parasite reaches approximately 1 mm in diameter
and is commonly observed in the gills and/or skin as coalescing white
spots, hence the common name. The
trophont or mature stage of the parasite has a large "horseshoe"
shaped nucleus, and the entire surface of the parasite is covered in
life cycle of this parasite is direct, but is spent, in part, off of
the host. The
trophont is within the epidermis of the host, until it leaves the
fish, encysts demonstrates
mature cyst of this parasite) and divides to produce many
host-seeking tomites. The
tomites penetrate the skin and gills of the fish to complete the life
life cycle is temperature dependent with a shorter life cycle
occurring at warmer water temperatures.
with a cutaneous infection will
"flash", i.e., turn over and expose their white underside,
whereas fish with a gill infection will "pipe", i.e., come to the
surface of the water and "breathe" through their mouth. Gill
lesions include epithelial hyperplasia with the presence of mature
trophonts within the gills. Cutaneous
lesions also exhibit focal epidermal hyperplasia, with parasites
being located beneath the hyperplastic epidermis.
is a motile ciliated protozoal parasite which causes disease in the
skin and gills of fish. It
is typically heart-shaped with the posterior end being broader and
slightly notched. It
measures approximately 20-40 m in width and 30-70 m
in length and its surface is covered with cilia. There
is a large macronucleus in the posterior portion of this organism and
a smaller micronucleus is near or within the macronucleus. This
parasite has been attributed to death of fish due to respiratory and
osmoregulatory imbalances associated with severe gill
is dependent upon demonstration of the organism within the affected
organs by either cytology or histopathology.
Cryptocaryon irritans, parasite of gills and skin, is the
causative agent of this disease. External signs consist of white
spots and mucous excess or ulcers on the skin and impairment of
respiratory function. Gill histopathology consist of inflammation,
haemorrhages, hyperplasia and lamellar destruction. This ciliate is a
typical marine fish parasite affecting commercial and ornamental fish
and producing high mortality in culture conditions. Outbreaks
appeared mainly at high temperatures. Some treatment and control
measures are similar to those recommended for ichthyophthiriasis,
though quinine derivatives and low salinity baths have also been
used. Diagnosis is based on macroscopical examination followed by
microscopical examination for confirming the presence of the ciliate.
The parasite can also be found in histopathological studies.
There are three genera which form the Trichodina complex: Trichodina, Trichodonella and Tripartiella, however, all three are commonly referred to as "Trichodina". All are approximately 100 m in diameter and have a saucer to "frisbee" shape and are ringed with cilia around its entire surface. They have a circular arrangement of tooth-like structures (denticular ring) within the body which provides them a characteristic appearance in fresh gill and skin cytology preparations (photo). Fish with severe gill infections of trichodina will have respiratory and osmoregulatory difficulty and may "pipe" as well as "flash" if there is cutaneous involvement. Fin erosions and/or ulcerations can be observed in chronic cutaneous infections. Diagnosis of this parasitic disease is dependent upon identification of the parasite within the skin or gill cytologic preparations or histopathology.
Fish trichodinids include mainly Trichodina spp.,
Trichodinella spp. and Tripartiella spp. These
peritrichid ciliates are more commensals than genuine ectoparasites,
but can produce different damages in massive infections. The fish
show a grey-blue turbid layer on the skin. Respiratory function can
be impaired in gill infections. Trichodinids parasitize a lot of
freshwater and marine fish species. Diagnosis is mainly based on
microscopical examination of fish or gill scraping preparations.
Hygiene in hatcheries and quarantine for ornamental fish are
recommended for prevention. This ciliatosis can be treated with
formaldehyde in baths. In freshawter ornamental fish and fry, baths
of salt solutions can be applied, with variable success.
are ciliated protozoal organisms which are thought to be free-living,
but have been known to parasitize fish. They are
sessile organisms with a cylindrical to conical body with oral cilia
and a permanent motionless equatorial ciliary fringe. They
range in size from approximately 60-100 m
and adhere to the epithelium of the skin and/or gills. Disease and
death of fish have been associated with chronic infections of the
gills due to mechanical blockage of respiratory epithelium. Diagnosis
of this parasite is dependent upon identification of this organism
within the skin or gill scrapings or histopathology.
Several species of the genera Uronema, Phylasterides and
Miamiensis have been recorded as facultative parasites of
different fish. Clinical signs of scuticociliatosis depend on the
parasite location. External signs include skin lesions or ulcers and
pigmentation changes, but the parasite frequently invade the body
muscle and the internal organs, which become destroyed by this
histophagous parasite. Nervous system can also be colonised, which
can be accompanied by erratic swimming, equilibrium loss or lethargy.
The disease cause severe infections and outbreaks in some cultured
fish and mortalities can reach 100% of some affected stocks.
Different fish species can be affected, but the most severe cases
reported deals with turbot, Mediterranean seabass, several marine
aquarium fish, Australian tunnids and Japanese flounder.
Diagnosis is based on the finding of ciliates in ascitic fluid or
scrapings of different organs. The typical morphology of
Scuticociliatida can be easily observed in fresh preparations at
light microscope, in stained smears or histological sections.
However, the identification at the genus and species level requires
specific staining evidencing the somatic and oral infraciliature and
the scutica. There are no efficacious treatment for this parasitosis.
Formalin baths have been assayed with certain success only in the
initial phase of infection.
B. Endoparasitic Protozoans
Different coccidia (Apicomplexa) are known from among freshwater and
marine parasites, but their pathological significance for the
cultures is very variable. The genera Eimeria, Goussia and
Cryptosporidium include the species more frequently reported from
cultured fish. In freshwater fish, G. carpelli parasitizes
different cyprinids and E. anguillae is typical of eels. In
marine fish, E. sparis and G. sparis have been reported
from Sparus aurata and E. dicentrarchi and E. bouixi
from Dicentrarchus labrax. Fish Cryptosporidium spp.
include species from seabream, seabass, turbot, and aquarium fish,
affecting mainly larvae and juvenile, with deleterious effects not
always very evident, but resulting in poor condition. C. molnari
is more frequent in seabream than in seabass. The species of
turbot is probably a new one. Diagnosis of fish coccidia is mainly
based on histopathology and/or on fresh examination at microscope.
Immunodiagnostic methods are available for some human and animal
species, but not for fish species. Control of animal coccidians is
based on the use of differentcoccidiostatics or coccidiocides, but
information regarding fish coccidia is very scarce. Furazolidone,
amprolium chloride and furanace, among others, have been tried to
treat different fish cocidia.
Microsporea are represented in fish by different genera, mainly
Enterocytozoon, Glugea, Loma, Pleistophora
and Tetramicra. In freshwater fish, Pleistophora and
Loma are relatively frequent. Among cultured marine fish,
there have been several reports of Plesitophora senegalensis in
gilthead seabream, whereas Glugea sp. and Tetramicra
brevifillum have been found in turbot. Pathological concern of
microsporidiosis in fish is dependent on location and infection
intensity. Variable loses in turbot cultures have been related to
Tetramicra infections. Diagnosis is based on the direct
detection of the parasite at microscope, mainly the spores, but
ultrastructural studies are necessary for identification at the
specific (or even generic) level. A PCR based assay has been recently
developed for T. brevifillum. Among chemicals tested for
treatment, toltrazuril has apparently given better results than
fumagillin and amprolium.
3. Myxosporea (myxosporidiosis):
The class Myxosporea (phylum Myxozoa) include numerous genera and
species, most of them parasites of fish. Some species are well know
pathogens for freshwater fish. In the last years Myxosporea have been
increasingly reported in cultured marine fish. They are characterised
by a spore with one to several valves, one or more infective
sporoplasms and one to several polar capsules with a coiled polar
The most pathogenic species belong to the genera Ceratomyxa,
Myxobolus, Myxidium, Spaherospora, Enteromyxum, Kudoa,
Tetracapsuloides and Sphaerospora.
In freshwater fish the most significant diseases are whirling
disease, PKD, sphaerosporosis and ceratomyxosis (produced by
Ceratomyxa shasta). Myxosporea reported from cultured marine
fish include species of the genera Ceratomyxa, Enteromyxum, Kudoa,
Lepthoteca, Sphaerospora and Sinuolinea. Other myxosporeans
reported ocassionally in the survey are Leptotheca sp. and
Polysporoplasma sparis from the kidney of S. aurata, and
Sinoulinea sp. from the urinary bladder of turbot, the three
reported only by 1 laboratory from Spain, mainly in routine or
occasional samplings. The species of Leptotheca has been
described as L. sparidarum from seabream an dentex.
3. Myxobolus cerebralis (Whirling disease)
The causative agent is Myxobolus cerebralis (synonym Myxosoma
cerebralis). Clinical signs include dark coloration of the
posterior part of the body and abnormal swimming in spiral, followed
by skull deformation and spinal curvature. Almost all salmonid
species can be infected, but susceptibility is very variable
according to the species. Oncorhynchus mykiss and other
Oncorhynchus spp. Are very susceptible, while Salmo trutta
is rather resistant. The involvement of an intermediate
oligochaete host in the life cycle of this myxosporean was
demonstrated 18 years ago. This knowledge has facilitated preventive
measures, consisting of the use of concrete or plastic ponds or tanks
and their frequent cleaning for avoiding the presence of oligochaetes
and thus the transmission of the disease.
This is very important, considering the limited efficacy of
treatments assayed till now (fumagillin, toltrazuril) for this
myxosporea and other species. In some European countries, the
incidence of whirling disease has clearly decreased, whereas in USA
whirling disease is widely distributed and is still an important
pathological problem. Diagnosis is based on the histological
examination of skull cartilage, or their enzymatic digestion followed
by microscopical observation of the typical spores. A PCR assay has
also been developed.
Hexamita / Spironucleus
parasites are pyriform to oval with tapering toward the posterior
rounded individuals can be identified. The
organisms are 6-8 m
wide and 10-12 m
have three pairs of anterior flagella which are approximately one and
one-half times the length of the body. The
flagella originate from the blepharoplast at the anterior end of the
organisms can reproduce by longitudinal binary fission as well as
undergo schizogony within the epithelial cells of the ceca or
parasite causes disease within the gastrointestinal tract of fish and
affected fish will have clinical signs related to malnutrition and
emaciation. Diagnosis is dependent upon finding the parasite
from cytologic scrapings of the ceca or intestinal tract or
histopathology of these organs. A
poorly understood parasite, thought to be Hexamita-like is
thought to be responsible for Freshwater Hole-in-the-Head and Lateral
Line Erosion (FHLLE).
C. Ectoparasitic flagellates
1. Ichthyobodo spp.(Costiasis)
Ichthyobodo sp. (also known as Costia) are the agents
of this disease of the gills and skin. I. necator is the
species parasitizing salmonids in freshwater, but a different species
is considered to be present in marine fish. Affected fish appear thin
and lethargic, and may show a grey-whitish pellicle on skin,
epidermic erosion or even haemorhages or ulcers, as well as gill
hyperplasy and edema. Costiasis is widely distributed in different
fish species, mainly in larval and juvenile stages, and mortality can
occur in fry or ornamental fish with moderate to severe infections.
Besides direct mortalities, indirect damage due to decreased health
condition and gill lesions must be considered.
Diagnosis is based on microscopical examination and histopathology.
Prevention relies on hygienic measures.
Costiasis can be treated with formaline 1:4000 or 1:6000 in baths
with a good aeration.
The other ectoparasitic flagellates found in the survey are the gill
Cryptobia spp., with a direct life cycle. Marine ectozoic
species include C. branchialis, from different coastal fish
and C. eilatica, described from the gills of Sparus aurata
and Diplodus noct in the Red Sea. In heavy infections, the
parasites produce gill hyperplasia and epithelial destruction, with
subsequent respiratory impairment. External signs are anorexia and
skin darkness. In the Mediterranean it is relatively common in
cultured seabass and seabream. The infection can produce trickling
but persistent mortalities, so loses can reach 10% after several
Diagnosis is based on microscopic fresh and histological examination.
Formalin baths (150 mg/l) can be effective for treatment.
D. Endoparasitic flagellates
1. Cryptobia spp., Trypanoplasma spp., Trypanosoma
Some species of these genera parasitize internal organs of fish.
Cryptobia iubilans is the only pathogenic intestinal species,
common in aquaria cichlid fish. Trypanoplasma spp. and
Trypanosoma spp. include parasites of the bloodstream and of
tissues, with indirect life cycles (leeches are the main vectors).
The best known is Trypanoplasma salmositica (frequently
referred as Cryptobia samositica) producing cryptobiasis of
salmonids. Clinical signs consist of exophthalmia, splenomegaly,
hepatomegaly, abdominal distension with ascites, anemia and anorexia.
Mortality is dependent on fish stocks and species, but may be high in
juveniles. The disease has severe impact in salmonid cultures in
North America. An experimental protective vaccine has been developed.
Other pathogenic species, Trypanoplasma borreli, parasitizes
mainly cyprinids in Europe and North America. The genus
Trypanosoma includes numerous species of both freshwater and
marine fish. Some freshwater species are pathogenic for cyprinids.
Hexamita spp. are parasites of the intestine and gall bladder
of freshwater fish, mainly salmonids but also cyprinids and
ornamental fish. Hexamitiasis, typical of weak fish, is frequent as a
secondary infection. Affected fish can show nervous behaviour, and
internally the intestine may appear pale. Mortalities can occur in
fry and ornamental fish. Diagnosis is manly based on the direct
observation of the flagellate in fresh intestinal scrapings or
Also known as "velvet disease", the causative agent is
Amyloodinium ocelatum, an ectoparasite on the skin and gills of
different fish species. Appart from the velvet appearance, clinical
signs consist of anorexia and scratching. Histopathological lesions
include gill inflammation, haemorrhages and hyperplasy. Massive
infections are frequently associated to mortalities, both in
mariculture and sea aquaria, mainly at high temperatures. The
infection is very common in Mediterranean fish, though other fish
species are affected, including tropical and aquarium fish. Other
dinoflagellates (as Piscinoodinium spp.) parasitize different
Diagnosis is mainly based on microscopic fresh and histological
examination, though an ELISA test is available. No effective control
measures are known for Mediterranean fish.
Freshwater (2-4 minutes) or copper sulphate (0.75 mg/l, 12-14 days)
baths have been suggested as an aid to control the trophonts or
dinospores, respectively. In Pacific threadfin (Polydactylus
sexfilis) recent findings suggest the suitability of hydrogen
peroxide as treatment in juvenile fish. Some evidences suggest the
development of immunity against re-infections, and specific
antibodies have been demonstrated in the sera of infected fish.
— Also known as Fish lice and is easy to detect with the naked eye
especially against the background of fins.
varies from between 1mm and 5mm.
themselves to the fish by suckers which damages the skin, they also
inject a poison into the body of the fish which causes inflammation,
bleeding and potentially secondary bacterial infection
treatments recommended to eradicate these parasites are either
Masoten, Dimilin or Paradex.
3. Mongenetic Trematodes
is a group of trematodes which complete their entire life cycle on
the host. The adults attach to the host by
a haptor or opishaptor which
is a specially adapted structure on the posterior end of the
parasite. This organ has hooks which allow the parasite to
attach firmly to the host fish. These parasites
usually cause minimal damage to fish, but will infest the skin, fin
and gills of pond fishes. Severe infestations may be
responsible for poor respiration and/or emaciation. The
two most common monogenetic trematodes
include: Dactylogyrus and Gyrodactylus.
Also known as Skin Fluke. Fish suffering from infestations of gill
flukes may suffer respiratory problems as the flukes begin to damage
the delicate gill tissues. Secondary bacterial infection often
occurs in fish left suffering from these parasites, due to the
physical damage caused by the anchors.
control of both types of fluke can be achieved with Chloramine T,
Malachite Green Formalin and Masoten, or Potassium Permanganate.
order to kill all generations, repeat treatments may be necessary,
the frequency being dependent on temperature and chemical
- The Gill Fluke
and Skin flukes are two of the family of monogenetic trematode
genera, all of which are characterized by the large grappling hooks
which are used to attach themselves to their victims.
are parasite affecting fish. They range from 0.05 to 3.00mm long and
there are actually a huge number of species in the genus
Lernaea - Anchor worm
is a common parasite which is clearly visible to the naked eye and
can reach 10 to 12mm.
parasite burrows its head into the fish tissue, under a scale and
only the body and tail are normally visible.
lay eggs which can lay undetected in the pond and can hatch when
conditions and water temperatures are right.
treatments will not affect the viability of eggs so repeat
treatments may be required to kill all generations.
4. Digenetic Trematodes
group of parasites has a complex life cycle with several successive
larval generations, alternating sexual and asexual generations and
changes of hosts to develop into the adult in its primary host. The
life cycles of trematodes involving fishes may either use fishes as
the primary hosts or as intermediate hosts. Adult
trematodes may infest the intestine or gall bladder of
fishes. A few of the more common digenetic trematodes are
4.1 Diplostomum spathaceum
The life cycle of this parasite begins as an adult trematode in the
intestine of gulls or other fish-eating birds. The body of
the adult is 0.3-0.5 cm in length and distinctly divided into a
flattened anterior forebody and a cylindrical and narrower
hindbody. Eggs are shed and passed in the feces of the
bird to the water. The eggs hatch in approximately 21 days
into free-swimming ciliated miracidia. The miracidia
infest aquatic snails as the first intermediate host by penetration
of the snail’s hepatopancreas. The miracidia then become
a mother sporocyst, followed by one or more daughter
sporocysts. Each daughter sporocyst produces many
cercariae which are released into the water. These
cercariae seek a second intermediate host by penetrating
the fins, skin, gills or cornea of small fishes. Primary
host fish which ingest the initially infected fish (second
intermediate host) become infected and the life-cycle is completed
when the host fish are ingested by fish-eating birds.
4.2 Posthodiplostomum minimum:
This trematode has several synonyms
minimum, Neodiplostomum orchilongum and Postodiplostomum
orchilongum. The life
cycle of this trematode is very similar to that of D.
although, infectivity of cercariae to fishes lasts no more than 24
hours after release from the snail. Each cercaria actively
raises a scale and enters under the scale pocket, causing irritation
to the fish. Blood, congestion and hemorrhage occur at the bases
of fins or other places of cercarial penetration. The
trematodes migrate from the point of entry to visceral organs of the
fishes, usually within one to three hours after
penetration. Metacercariae are located in any organ of the
fishes' body, but are generally more numerous in the liver, kidney,
heart, spleen and other organs of abdominal viscera. With
many of the digenetic trematodes, the metacercariae within the skin
results in increased melanin deposition, hence the term "black spot
disease". Visible white or yellow spots in the visceral organs,
usually no larger than 1 mm in diameter are often referred to as
"white grubs" or "yellow grubs" and could be caused by
several trematode species. Diagnosis of digenetic trematode
infections is dependent upon identification of the genus and species
of the trematode within infected fish.
Seafood — Fish — Crustacea
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