notes

1. Identification of Fish
Parasites
Sameer G Chebbi
Industrial Fish and Fisheries
Dept. of Zoology
Karnatak Science College,
Dharwad

2. Trypanosoma
 Trypanosoma is genus of kinetoplastids (class Kinetoplastida),
a monophyletic group of unicellular parasitic flagellate protozoa.
 All trypanosomes are heteroxenous (requiring more than one
obligatory host to complete life cycle) and most are transmitted
via a vector.
 The majority of species are transmitted by blood-
feeding invertebrates, but there are different mechanisms among
the varying species.
 In an invertebrate host they are generally found in the intestine,
but normally occupy the bloodstream or
an intracellular environment in the vertebrate host.
 T. sinipercae, in fishes causes the sucks the blood and it will leads
to secondary infection.
 Piscine haemoflagellates swim freely in the blood. Members of the
genus Trypanosoma are spindle shaped, 25–95 μm long, a single
flagellum originating from a usually apical kinetoplast is connected
longitudinally to the trypanosome body by an undulating
membrane.
 The nucleus is usually single, except in the course of division and
centrally positioned.
 Natural infection with trypanosomes may be very common,
particularly where the leech vector is also common.
 At present the only practical means which may be recommended
is environmental control by elimination of leeches.

4. Ichthyophthiriasis multifilis:
 This 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 cilia.
 The 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 and divides to produce many host-seeking tomites.
 The tomites penetrate the skin and gills of the fish to complete the life
cycle.
 The life cycle is temperature dependent with a shorter life cycle occurring
at warmer water temperatures.
 Fish 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.
 Ichthyophthiriasis is fatal to fish of all sizes. Chronic infection will cause
serious damage to the skin, fin and gills; corneal infection impairs vision

7. Dactylogyrus
 This 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.
 This parasite is approximately 0.2 to 0.5 mm in length, reaching a
maximum length of 2.0 mm.
 It has seven pairs of marginal hooks and usually one pair of median
hooks on the opishaptor.
 The dactylogrids have two to four pigmented spots (known as “eyes”
or “eye spots”) in the anterior fourth of the body.
 All dactylogrids are oviparous with no uterus.

9. ERGASILIDAE (COPEPODA)
 It is crustacean parasite in fish and It will affect many fishes of Freshwater and
euryhaline fish of many families.
 Common in fish of all major water systems.
 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 the
genus Paraergasilus, may attach to sites other than gills.
 The cephalothorax constitutes half or more of body length, the first of four
thoracopodes occurs at about mid-length.
 Segmentation of the thorax (except the first segment, fused with the head) and of
the abdomen is distinct.
 The second antenna terminal segment is hook-like in Ergasilus and three clawed
in Paraergasilus.
 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.
 Males 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 (lasting
from 10 days to over a month).
 Ergasilids attached to gill filaments produce small foci of erosion; apparently feeding
involves excretion of proteolytic enzymes for external digestion. Such erosion
processes occur in E. megacheir infections in cichlids.
 Erosion and degradation processes may extend beyond the epithelial lining, resulting
in obstructed branchial blood vessels.
 Irritation often results in responsive hyperplasia of the epithelium, which, as infection
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 the gills

11. Lernaea cyprinacea
 Lernaea cyprinacea, an opportunistic species infecting fish of many families.
 The 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 buccal
mucosa.
 Larval stages, copepodites and copepod-shaped males are attached to the gills.
 Differentiation to lernaeid genera and to species in the genus Lernaea is based
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 the
consistency of the tissue into which the holdfast organ is anchored.
 Both copepodites infecting gills, and females infecting any site on the fish
integument, may harm the fish.
 Heavy infection of gills by copepodites of L. barnimiana or L. cyprinacea causes
damage to the tissue which is in immediate contact with the parasite and stimulates
extensive hyperplasia of the entire gill epithelium.
 Copepodite infections are potentially lethal to small fish, while large fish (such
as Bagrus) will tolerate extremely heavy gill infections.
 The attachment of the adult females to the integument stimulates an intense
inflammatory response.
 The tissue around the anchor turns into a granuloma or necrotic lesion, and is later
transformed into a fibrotic encapsulation.
 Economic 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 fish
unsuitable for sale.
 Parasitic females of lernaeids are tolerant to organophosphate and organohalogen
insecticides. A dip in potassium permanganate.

13. ARGULIDAE (BRANCHIURA)
 Argulus africanus and Dolops ranarum are opportunists and occur in diverse fish in all
major systems.
 Argulids (“fish lice”) are dorso-ventrally flattened and covered dorsally by a rounded
or horseshoe shaped carapace.
 Ventrally positioned head appendages are developed for attachment, four thoracic
segments each bear a pair of bifid swimming legs.
 The abdomen is comprised of a single bi-lobed unit which contains testes or a round
seminal receptacle.
 Argulus in having the second maxilla armed with a hook rather than a sucker,
characteristic of the latter.
 Chonopeltis 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 of
the second maxilla is distinctly developed. The carapace is reduced in size and width.
Unlike the above argulids, which are active swimmers, Chonopeltis is not capable of
swimming if removed from the host.
 Species of Argulus and Dolops ranarum are parasitic throughout life, but leave the
host 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.
 Argulids infecting the skin or mouth of fish induce severe local damage to the
integument.
 Damage 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,
inflamed wounds.
 Attachment to and crawling on the skin also causes irritation and abrasions leading
first to proliferation and later to desquamation and erosion of the epithelium.
 Damage is quickly alleviated where parasites can actively change attachment sites.
 When a shift of attachment site is slowed or prevented by overcrowding, in heavy
infections, particularly with site specific parasite species, chronic inflammation
develops, the infected surface of the integument ulcerates, the epithelium is
destroyed and the dermis becomes exposed.
 Both organohalogen and organophosphate insecticides effectively kill agulids with
reliable safety margins to fish.

15. PARASITIC ISOPODA
 Isopoda 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,
including grey mullets .
 A few species of cymothoid isopods (Lironeca spp.) occur in freshwater fish
(apparently as marine relics).
 Opportunistic euryhaline cymothoids of several families and genera infect farmed fish
in Southeast Asia, including cultured tilapia.
 Isopoda 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,
a pair of variable sized eyes and a mouth.
 The 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, with
pairs of pleopods, except the last which together with biramous uropods form a
swimming tail pleotelson.
 The ‘cymothoid’ isopods attach to fish early in life and pass through a male stage
before becoming female.
 The presence of a mature female prevents male stage specimens from further
development. Both males and females remain permanently attached to the fish.
 Egg and larval development takes place in a special brood-pouch on the females
ventrum.
 Another group, the ‘gnathiid’ isopods, are marine and only parasitic during the larval
stage.
 Isopoda 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.
The host specific ones are the least harmful to their hosts.
 Even host specific species attached and causing degenerative changes in the tongue
cartilage do not cause clinical harm to the fish.
 With 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.
 Their 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.
 Lesion to the integument causes hyperplasia, or desquamation and later on dermal

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

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