fish parasite

1. Identification of FishIdentification of Fish
ParasitesParasites
Sameer G ChebbiSameer G Chebbi
Industrial Fish and FisheriesIndustrial Fish and Fisheries
Dept. of ZoologyDept. of Zoology
Karnatak Science College,Karnatak Science College,
DharwadDharwad

2. TrypanosomaTrypanosoma TrypanosomaTrypanosoma isis genusgenus ofof kinetoplastidskinetoplastids (class Kinetoplastida),(class Kinetoplastida),
aa monophyleticmonophyletic group of unicellulargroup of unicellular parasiticparasitic flagellateflagellate protozoaprotozoa..
 All trypanosomes are heteroxenous (requiring more than oneAll trypanosomes are heteroxenous (requiring more than one
obligatory host to complete life cycle) and most are transmittedobligatory host to complete life cycle) and most are transmitted
via avia a vectorvector..
 The majority of species are transmitted by blood-The majority of species are transmitted by blood-
feeding invertebrates, but there are different mechanisms amongfeeding invertebrates, but there are different mechanisms among
the varying species.the varying species.
 In an invertebrate host they are generally found in the intestine,In an invertebrate host they are generally found in the intestine,
but normally occupy the bloodstream orbut normally occupy the bloodstream or
an intracellular environment in the vertebrate host.an intracellular environment in the vertebrate host.
 T. sinipercaeT. sinipercae, in fishes causes the sucks the blood and it will leads, in fishes causes the sucks the blood and it will leads
to secondary infection.to secondary infection.
 PiscinePiscine haemoflagellateshaemoflagellates swim freely in the blood. Members of theswim freely in the blood. Members of the
genusgenus TrypanosomaTrypanosoma are spindle shaped, 25–95 μm long, a singleare spindle shaped, 25–95 μm long, a single
flagellum originating from a usually apicalflagellum originating from a usually apical kinetoplastkinetoplast is connectedis connected
longitudinally to the trypanosome body by an undulatinglongitudinally to the trypanosome body by an undulating
membrane.membrane.
 The nucleus is usually single, except in the course of division andThe nucleus is usually single, except in the course of division and
centrally positioned.centrally positioned.
 Natural infection withNatural infection with trypanosomestrypanosomes may be very common,may be very common,
particularly where the leech vector is also common.particularly where the leech vector is also common.
 At present the only practical means which may be recommendedAt present the only practical means which may be recommended
is environmental control by elimination of leeches.is environmental control by elimination of leeches.

4. Ichthyophthiriasis multifilis:Ichthyophthiriasis multifilis:  This is probably the most common parasite of all fishes.This is probably the most common parasite of all fishes.
 The common name for this parasite and disease is “Ich” or “white spot”.The common name for this parasite and disease is “Ich” or “white spot”.
The mature parasite reaches approximately 1 mm in diameter and isThe mature parasite reaches approximately 1 mm in diameter and is
commonly observed in the gills and/or skin as coalescing white spots,commonly observed in the gills and/or skin as coalescing white spots,
hence the common name.hence the common name.
 The trophont or mature stage of the parasite has a large “horseshoe”The trophont or mature stage of the parasite has a large “horseshoe”
shaped nucleus, and the entire surface of the parasite is covered in cilia.shaped nucleus, and the entire surface of the parasite is covered in cilia.
 The life cycle of this parasite is direct, but is spent, in part, off of theThe life cycle of this parasite is direct, but is spent, in part, off of the
host.host.
 The trophont is within the epidermis of the host, until it leaves the fish,The trophont is within the epidermis of the host, until it leaves the fish,
encysts and divides to produce many host-seeking tomites.encysts and divides to produce many host-seeking tomites.
 The tomites penetrate the skin and gills of the fish to complete the lifeThe tomites penetrate the skin and gills of the fish to complete the life
cycle.cycle.
 The life cycle is temperature dependent with a shorter life cycle occurringThe life cycle is temperature dependent with a shorter life cycle occurring
at warmer water temperatures.at warmer water temperatures.
 Fish with a cutaneous infection will “flash”, i.e., turn over and expose theirFish 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 towhite underside, whereas fish with a gill infection will “pipe”, i.e., come to
the surface of the water and “breathe” through their mouth.the surface of the water and “breathe” through their mouth.
 Gill lesions include epithelial hyperplasia with the presence of matureGill lesions include epithelial hyperplasia with the presence of mature
trophonts within the gills.trophonts within the gills.
 Cutaneous lesions also exhibit focal epidermal hyperplasia, with parasitesCutaneous lesions also exhibit focal epidermal hyperplasia, with parasites
being located beneath the hyperplastic epidermis.being located beneath the hyperplastic epidermis.
 IchthyophthiriasisIchthyophthiriasis is fatal to fish of all sizes. Chronic infection will causeis fatal to fish of all sizes. Chronic infection will cause
serious damage to the skin, fin and gills; corneal infection impairs visionserious damage to the skin, fin and gills; corneal infection impairs vision

7. DactylogyrusDactylogyrus
 This is a group of trematodes which complete their entire life cycle onThis is a group of trematodes which complete their entire life cycle on
the host.the host.
 The adults attach to the host by a haptor or opishaptor which is aThe adults attach to the host by a haptor or opishaptor which is a
specially adapted structure on the posterior end of the parasite.specially adapted structure on the posterior end of the parasite.
 This organ has hooks which allow the parasite to attach firmly to theThis organ has hooks which allow the parasite to attach firmly to the
host fish.host fish.
 These parasites usually cause minimal damage to fish, but will infestThese parasites usually cause minimal damage to fish, but will infest
the skin, fin and gills of pond fishes.the skin, fin and gills of pond fishes.
 Severe infestations may be responsible for poor respiration and/orSevere infestations may be responsible for poor respiration and/or
emaciation.emaciation.
 The two most common monogenetic trematodesThe two most common monogenetic trematodes
include: Dactylogyrus and Gyrodactylus.include: Dactylogyrus and Gyrodactylus.
 This parasite is approximately 0.2 to 0.5 mm in length, reaching aThis parasite is approximately 0.2 to 0.5 mm in length, reaching a
maximum length of 2.0 mm.maximum length of 2.0 mm.
 It has seven pairs of marginal hooks and usually one pair of medianIt has seven pairs of marginal hooks and usually one pair of median
hooks on the opishaptor.hooks on the opishaptor.
 The dactylogrids have two to four pigmented spots (known as “eyes”The dactylogrids have two to four pigmented spots (known as “eyes”
or “eye spots”) in the anterior fourth of the body.or “eye spots”) in the anterior fourth of the body.
 All dactylogrids are oviparous with no uterus.All dactylogrids are oviparous with no uterus.

9. ERGASILIDAE (COPEPODA)ERGASILIDAE (COPEPODA) It is crustacean parasite in fish and It will affect many fishes of Freshwater andIt is crustacean parasite in fish and It will affect many fishes of Freshwater and
euryhaline fish of many families.euryhaline fish of many families.
 Common in fish of all major water systems.Common in fish of all major water systems.
 Several species occur in cichlids, in siluriforms and also in brackish waters.Several species occur in cichlids, in siluriforms and also in brackish waters.
 Only subadult and adult females occur of fish, mostly on the gills, a few of theOnly subadult and adult females occur of fish, mostly on the gills, a few of the
genusgenus ParaergasilusParaergasilus, may attach to sites other than gills., may attach to sites other than gills.
 The cephalothorax constitutes half or more of body length, the first of fourThe cephalothorax constitutes half or more of body length, the first of four
thoracopodes occurs at about mid-length.thoracopodes occurs at about mid-length.
 Segmentation of the thorax (except the first segment, fused with the head) and ofSegmentation of the thorax (except the first segment, fused with the head) and of
the abdomen is distinct.the abdomen is distinct.
 The second antenna terminal segment is hook-like inThe second antenna terminal segment is hook-like in ErgasilusErgasilus and three clawedand three clawed
inin ParaergasilusParaergasilus..
 Eggs are clustered in a bunch rather than arranged in a single line.Eggs are clustered in a bunch rather than arranged in a single line.
 In Ergasilidae only the female is parasitic, and is found on the gills of fish.In Ergasilidae only the female is parasitic, and is found on the gills of fish.
 Males are free-living and there is a prolonged, free-living larval development whichMales are free-living and there is a prolonged, free-living larval development which
includes three to six stages of nauplii and four to six stages of copepodites (lastingincludes three to six stages of nauplii and four to six stages of copepodites (lasting
from 10 days to over a month).from 10 days to over a month).
 Ergasilids attached to gill filaments produce small foci of erosion; apparently feedingErgasilids attached to gill filaments produce small foci of erosion; apparently feeding
involves excretion of proteolytic enzymes for external digestion. Such erosioninvolves excretion of proteolytic enzymes for external digestion. Such erosion
processes occur inprocesses occur in E. megacheirE. megacheir infections in cichlids.infections in cichlids.
 Erosion and degradation processes may extend beyond the epithelial lining, resultingErosion and degradation processes may extend beyond the epithelial lining, resulting
in obstructed branchial blood vessels.in obstructed branchial blood vessels.
 Irritation often results in responsive hyperplasia of the epithelium, which, asIrritation often results in responsive hyperplasia of the epithelium, which, as
infection is prolonged, may extend over large areas of the gills, causing fusion andinfection is prolonged, may extend over large areas of the gills, causing fusion and
embedding of lamellae, with a resulting decrease in the respiratory function of theembedding of lamellae, with a resulting decrease in the respiratory function of the
gillsgills

11. Lernaea cyprinaceaLernaea cyprinacea Lernaea cyprinaceaLernaea cyprinacea, an opportunistic species infecting fish of many families., an opportunistic species infecting fish of many families.
 The rod-shaped, unsegmented, or partly segmented parasitic stage lernaeid femaleThe rod-shaped, unsegmented, or partly segmented parasitic stage lernaeid female
is anchored, with the aid of a specialised holdfast organ, to the host skin or buccalis anchored, with the aid of a specialised holdfast organ, to the host skin or buccal
mucosa.mucosa.
 Larval stages, copepodites and copepod-shaped males are attached to the gills.Larval stages, copepodites and copepod-shaped males are attached to the gills.
 Differentiation to lernaeid genera and to species in the genusDifferentiation to lernaeid genera and to species in the genus LernaeaLernaea is basedis based
mainly on the morphology of the holdfast organ (anchors) of the parasitic females.mainly on the morphology of the holdfast organ (anchors) of the parasitic females.
 The growth and branching of the latter, however, is greatly affected by theThe growth and branching of the latter, however, is greatly affected by the
consistency of the tissue into which the holdfast organ is anchored.consistency of the tissue into which the holdfast organ is anchored.
 Both copepodites infecting gills, and females infecting any site on the fishBoth copepodites infecting gills, and females infecting any site on the fish
integument, may harm the fish.integument, may harm the fish.
 Heavy infection of gills by copepodites ofHeavy infection of gills by copepodites of L. barnimianaL. barnimiana oror L. cyprinaceaL. cyprinacea causescauses
damage to the tissue which is in immediate contact with the parasite and stimulatesdamage to the tissue which is in immediate contact with the parasite and stimulates
extensive hyperplasia of the entire gill epithelium.extensive hyperplasia of the entire gill epithelium.
 Copepodite infections are potentially lethal to small fish, while large fish (suchCopepodite infections are potentially lethal to small fish, while large fish (such
asas BagrusBagrus) will tolerate extremely heavy gill infections.) will tolerate extremely heavy gill infections.
 The attachment of the adult females to the integument stimulates an intenseThe attachment of the adult females to the integument stimulates an intense
inflammatory response.inflammatory response.
 The tissue around the anchor turns into a granuloma or necrotic lesion, and is laterThe tissue around the anchor turns into a granuloma or necrotic lesion, and is later
transformed into a fibrotic encapsulation.transformed into a fibrotic encapsulation.
 Economic losses due to infection not only results from direct harm to the fish, butEconomic losses due to infection not only results from direct harm to the fish, but
also from disfigurement which renders both fish grown for food and ornamental fishalso from disfigurement which renders both fish grown for food and ornamental fish
unsuitable for sale.unsuitable for sale.
 Parasitic females of lernaeids are tolerant to organophosphate and organohalogenParasitic females of lernaeids are tolerant to organophosphate and organohalogen
insecticides. A dip in potassium permanganate.insecticides. A dip in potassium permanganate.

13. ARGULIDAE (BRANCHIURA)ARGULIDAE (BRANCHIURA) Argulus africanusArgulus africanus andand Dolops ranarumDolops ranarum are opportunists and occur in diverse fish inare opportunists and occur in diverse fish in
all major systems.all major systems.
 Argulids (“fish lice”) are dorso-ventrally flattened and covered dorsally by a roundedArgulids (“fish lice”) are dorso-ventrally flattened and covered dorsally by a rounded
or horseshoe shaped carapace.or horseshoe shaped carapace.
 Ventrally positioned head appendages are developed for attachment, four thoracicVentrally positioned head appendages are developed for attachment, four thoracic
segments each bear a pair of bifid swimming legs.segments each bear a pair of bifid swimming legs.
 The abdomen is comprised of a single bi-lobed unit which contains testes or a roundThe abdomen is comprised of a single bi-lobed unit which contains testes or a round
seminal receptacle.seminal receptacle.
 ArgulusArgulus in having the second maxilla armed with a hook rather than a sucker,in having the second maxilla armed with a hook rather than a sucker,
characteristic of the latter.characteristic of the latter.
 ChonopeltisChonopeltis are usually the smallest; head appendages are feeble and rudimentary,are usually the smallest; head appendages are feeble and rudimentary,
the mouth tube found in the other argulids is absent, whereas the cup-like sucker ofthe mouth tube found in the other argulids is absent, whereas the cup-like sucker of
the second maxilla is distinctly developed. The carapace is reduced in size and width.the second maxilla is distinctly developed. The carapace is reduced in size and width.
Unlike the above argulids, which are active swimmers,Unlike the above argulids, which are active swimmers, ChonopeltisChonopeltis is not capable ofis not capable of
swimming if removed from the host.swimming if removed from the host.
 Species ofSpecies of ArgulusArgulus andand Dolops ranarumDolops ranarum are parasitic throughout life, but leave theare parasitic throughout life, but leave the
host to moult or to lay eggs, and during this process will also change hosts. Bothhost to moult or to lay eggs, and during this process will also change hosts. Both
males and females may survive free living for as long as 15 days.males and females may survive free living for as long as 15 days.
 Argulids infecting the skin or mouth of fish induce severe local damage to theArgulids infecting the skin or mouth of fish induce severe local damage to the
integument.integument.
 Damage is caused by the piercing proboscis stylet which enters deep into the skin'sDamage is caused by the piercing proboscis stylet which enters deep into the skin's
dermal layer and secretes lytic and toxic substances resulting in acute haemorrhagic,dermal layer and secretes lytic and toxic substances resulting in acute haemorrhagic,
inflamed wounds.inflamed wounds.
 Attachment to and crawling on the skin also causes irritation and abrasions leadingAttachment to and crawling on the skin also causes irritation and abrasions leading
first to proliferation and later to desquamation and erosion of the epithelium.first to proliferation and later to desquamation and erosion of the epithelium.
 Damage is quickly alleviated where parasites can actively change attachment sites.Damage is quickly alleviated where parasites can actively change attachment sites.
 When a shift of attachment site is slowed or prevented by overcrowding, in heavyWhen a shift of attachment site is slowed or prevented by overcrowding, in heavy
infections, particularly with site specific parasite species, chronic inflammationinfections, particularly with site specific parasite species, chronic inflammation
develops, the infected surface of the integument ulcerates, the epithelium isdevelops, the infected surface of the integument ulcerates, the epithelium is
destroyed and the dermis becomes exposed.destroyed and the dermis becomes exposed.
 Both organohalogen and organophosphate insecticides effectively kill agulids withBoth organohalogen and organophosphate insecticides effectively kill agulids with
reliable safety margins to fish.reliable safety margins to fish.

15. PARASITIC ISOPODAPARASITIC ISOPODA Isopoda are parasites of marine fish and infections have been reported in euryhalineIsopoda are parasites of marine fish and infections have been reported in euryhaline
fish in estuaries. Nerocila orbignyi, a common parasite of marine and estuarine fish,fish in estuaries. Nerocila orbignyi, a common parasite of marine and estuarine fish,
including grey mullets .including grey mullets .
 A few species of cymothoid isopods (Lironeca spp.) occur in freshwater fishA few species of cymothoid isopods (Lironeca spp.) occur in freshwater fish
(apparently as marine relics).(apparently as marine relics).
 Opportunistic euryhaline cymothoids of several families and genera infect farmed fishOpportunistic euryhaline cymothoids of several families and genera infect farmed fish
in Southeast Asia, including cultured tilapia.in Southeast Asia, including cultured tilapia.
 Isopoda are the largest crustaceans found on fish (20–50 mm long). The bodyIsopoda are the largest crustaceans found on fish (20–50 mm long). The body
consists of three regions, the head is unsegmented and bears two pairs of antennae,consists of three regions, the head is unsegmented and bears two pairs of antennae,
a pair of variable sized eyes and a mouth.a pair of variable sized eyes and a mouth.
 The maxilliped covers all other mouth parts, a second region, the peraeon, of 7The maxilliped covers all other mouth parts, a second region, the peraeon, of 7
segments, each with a pair of legs (peraeopods) and a six segmented pleon, withsegments, each with a pair of legs (peraeopods) and a six segmented pleon, with
pairs of pleopods, except the last which together with biramous uropods form apairs of pleopods, except the last which together with biramous uropods form a
swimming tail pleotelson.swimming tail pleotelson.
 The ‘cymothoid’ isopods attach to fish early in life and pass through a male stageThe ‘cymothoid’ isopods attach to fish early in life and pass through a male stage
before becoming female.before becoming female.
 The presence of a mature female prevents male stage specimens from furtherThe presence of a mature female prevents male stage specimens from further
development. Both males and females remain permanently attached to the fish.development. Both males and females remain permanently attached to the fish.
 Egg and larval development takes place in a special brood-pouch on the femalesEgg and larval development takes place in a special brood-pouch on the females
ventrum.ventrum.
 Another group, the ‘gnathiid’ isopods, are marine and only parasitic during the larvalAnother group, the ‘gnathiid’ isopods, are marine and only parasitic during the larval
stage.stage.
 Isopoda may be either highly host specific, opportunistic in their choice of hosts orIsopoda may be either highly host specific, opportunistic in their choice of hosts or
facultative parasites, attaching to fish if they are weak or trapped in nets or cages.facultative parasites, attaching to fish if they are weak or trapped in nets or cages.
The host specific ones are the least harmful to their hosts.The host specific ones are the least harmful to their hosts.
 Even host specific species attached and causing degenerative changes in the tongueEven host specific species attached and causing degenerative changes in the tongue
cartilage do not cause clinical harm to the fish.cartilage do not cause clinical harm to the fish.
 With the opportunistic and facultative parasites, the degree of damage to fish variesWith the opportunistic and facultative parasites, the degree of damage to fish varies
with the site of attachment and ratio between the isopod and the host.with the site of attachment and ratio between the isopod and the host.
 Their a priori large size is likely to cause pressure damage and abrasions, if attachedTheir a priori large size is likely to cause pressure damage and abrasions, if attached
to fish skin, and even more so inside the gill chamber.to fish skin, and even more so inside the gill chamber.
 Lesion to the integument causes hyperplasia, or desquamation and later on dermalLesion to the integument causes hyperplasia, or desquamation and later on dermal

17. MICROSPORAMICROSPORA Microsporidian infection has been described from many HolarcticMicrosporidian infection has been described from many Holarctic
marine and freshwater fish. There are very few reports ofmarine and freshwater fish. There are very few reports of
infections in fish in the tropics.infections in fish in the tropics.
 Microsporidia are obligate intracellular parasites. Infected cellsMicrosporidia are obligate intracellular parasites. Infected cells
usually enlarge to accommodate the proliferating parasite.usually enlarge to accommodate the proliferating parasite.
 Such enlarged cells are termed xenomas. Within these xenomas,Such enlarged cells are termed xenomas. Within these xenomas,
parasites undergo merogonous and sporogonous developmentparasites undergo merogonous and sporogonous development
which culminates in the production of spores .which culminates in the production of spores .
 Hypertrophic infected cells may reach macroscopic sizes and oftenHypertrophic infected cells may reach macroscopic sizes and often
yield characteristic gross pathological signs; multiple whitishyield characteristic gross pathological signs; multiple whitish
nodules in tissues, or in case of the swimbladder, a significantnodules in tissues, or in case of the swimbladder, a significant
thickening of the walls.thickening of the walls.
 All active stages of the microsporidians develop in the host cell.All active stages of the microsporidians develop in the host cell.
Two microsporidia were reported to develop within the host cellTwo microsporidia were reported to develop within the host cell
nucleus and and in haematopoietic cells.nucleus and and in haematopoietic cells.
 The effect of microsporidian infection on the piscine host isThe effect of microsporidian infection on the piscine host is
variable: fish seem to survive infections, in spite of the presencevariable: fish seem to survive infections, in spite of the presence
of huge xenomata often pressing on and displacing importantof huge xenomata often pressing on and displacing important
organs, while infection by some microsporidians undoubtedly hasorgans, while infection by some microsporidians undoubtedly has
a morbid effect on the fish. Intranuclear infection ofa morbid effect on the fish. Intranuclear infection of
haematopoietic cells was associated with acute anaemia.haematopoietic cells was associated with acute anaemia.
 There is no routine treatment. Fumagilin DCH used toThere is no routine treatment. Fumagilin DCH used to
controlcontrol NosemaNosema infections in bees has been tested for efficacy ininfections in bees has been tested for efficacy in
treatment of microsporidial infections in fish.treatment of microsporidial infections in fish.

19. THE ASIAN TAPE WORMTHE ASIAN TAPE WORM Bothriocephalus acheilognathiiBothriocephalus acheilognathii
 Known world-wide from fish of the families fishes.Known world-wide from fish of the families fishes.
 the life history ofthe life history of B. acheilognathiiB. acheilognathii involves a definitive host, ainvolves a definitive host, a
fish and an intermediate host, a copepod.fish and an intermediate host, a copepod.
 The Asian tape worm seems to be a thermophilic species.The Asian tape worm seems to be a thermophilic species.
 Low temperatures seem to delay or even interrupt developmentLow temperatures seem to delay or even interrupt development
and consequently completion of the life cycle.and consequently completion of the life cycle.
 At 28–30°C, 77% of the eggs hatched in the first day afterAt 28–30°C, 77% of the eggs hatched in the first day after
release, the remainder during the following five days.release, the remainder during the following five days.
 At 14–15°C, the incubation period extended to 10–28 days andAt 14–15°C, the incubation period extended to 10–28 days and
was for all practical purposes interrupted below 12°C.was for all practical purposes interrupted below 12°C.
 Heavily infected fish have a distended abdomen. SometimesHeavily infected fish have a distended abdomen. Sometimes
infected fish also develop a variable degree of aseptic dropsy.infected fish also develop a variable degree of aseptic dropsy.
 Tapeworm-infected carp suffered from high mortalities.Tapeworm-infected carp suffered from high mortalities.
 high mortality among heavily infected juvenile carp (90%) andhigh mortality among heavily infected juvenile carp (90%) and
also report pathological changes in infected fish, which includealso report pathological changes in infected fish, which include
pressure lesions, inflammation of the intestine and severepressure lesions, inflammation of the intestine and severe
“catarrhal-haemorrhagic enteritis” at the parasite attachment“catarrhal-haemorrhagic enteritis” at the parasite attachment
point, with proliferation of the peripheral connective tissue.point, with proliferation of the peripheral connective tissue.
 Several chemotherapeutic formulations, when applied in food,Several chemotherapeutic formulations, when applied in food,
effectively relieved fish from infection. Drugs should be mixedeffectively relieved fish from infection. Drugs should be mixed
in oil (corn, soy, fish) and sprayed on to pellets or mixed within oil (corn, soy, fish) and sprayed on to pellets or mixed with
feeds at a rate of one litre per 70kg dry weight.feeds at a rate of one litre per 70kg dry weight.