Classification of parasites

4.1.1 Classification of parasites

·        Following are the important fish parasites belonging to different groupof invertebrates.

·        Protozoa

·        Single celled eukaryoticorganisms. Classification - Levine et al. 1980

·        Phylum Sarcomastigophora - Flagella / pseudopodia presentand single nucleus.

·        Subphylum Mastigophora. -

·        ClassPhytomastigophorea - contain chloroplasts in their cytoplasm -dinoflagellate parasites Oodinium / Piscinoodinium sp. and Amyloodiniumsp.

·        ClassZoomastigophorea - do not possess chloroplasts and have a varying number offlagella

·        Order:Kinetoplastida - one or two flagella. Cryptobia and Trypanosoma.

·        Order:Retortamonodida- two to four flagella, bodinid parasites of Ichthyobodo sp.

·        Order:Diplomonadida - one to four flagella - Hexamita

·        Subphylum Sarcodina

·        Order:Amoebida - amoebae possess pseudopodia - divide by asexual fission.

·        Phylum Apicomplexa

·        ClassSporozoea.

·        Order:Eucoccidiorida. - Haemogregarina,Eimeria, Cryptosporidia and Goussia.

·        Phylum Microspora - obligatory and intracellular parasites.

·        ClassMicrosporea -Microsporidium, Pleistophora and Glugea.

·        Phylum Myxozoa

·        ClassMyxosporea. Order: Bivalvulida. Spore- 2valves. - Myxidium, Sphaerospora, Ceratomyxa and Myxobolus.

·        Order:Multivalvulida. Spores with 3 or more valves. Kudoa.

·        Phylum Ciliophora

·        ClassKinetofragminophorea. Oral ciliature slightly distinct from body ciliature.

·        SubclassVestibuliferia. Includes Balantidium.

·        SubclassHypostomatia. Includes Chilodonella

·        SubclassSuctoria. Possess suctorial tentacles, adult sessile. Includes Trichophyra.

·        ClassOligohymenophorea. Oral ciliature distinct from somatic ciliature.

·        SubclassHymenostomatia. - Ichthyophthirius.

·        SubclassPeritrichia - Epistylisand Trichodina.

·        Phylum Platyhelminthes - flatworms.dorso-ventrally flattened, bilaterally symmetrical and acoelomate lack an anusand specialized skeletal, circulatory and respiratory systems. Majoritymonoecious

·        Class Monogenea. The monogeneans - no intermediate hosts - small worms< 3 cm in length. - haptor, armed with hooks or suckers.

·        sub-classes Monopisthocotylea and Polyopisthocotylea.

·        SubclassMonopisthocotylea. Gyrodactylidae (viviparous, parasitic on skin, gill and fins,0.3-1 mm) and Dactylogyridae (gill parasite, oviparous, 2mm).

·        SubclassPolypisthocotylea.

·        ClassDigenea. -endoparasitic - metacercarial stages – encysted in fish

·        ClassCestoidea - endoparasitic - scolex - parasitic in intestine

·        Phylum Nematoda - bilaterally symmetrical-cylindrical body tapering at both ends. They possess gut and are sexuallydimorphic.

·        Phylum Acanthocephala - elongate cylindrical worms having retractile proboscis bearing hooks. They have no guts and the sexes areseparate.

·        Phylum Mollusca The larvae of fresh-water bivalve molluscs are often found attached to the gills and outer surfaces of fish. The larvae have thin bivalve shells often with little hooks on their inner edge.

·        Phylum Arthropoda

·        Class Crustacea - Crustaceans are bilaterally symmetrical animals with segmented bodieshaving jointed appendages. The body is covered with a rigid chitinoidexoskeleton.

·        Subclass Branchiura. Body flattened dorsoventrally -prehensilesuckers, They also have pre-oral proboscis. e.g. Argulus.

·        Subclass Copepoda. Mainly ectoparasitic in fish. Ergasilu s, Lernaea Cyclopidea, Caligidea andLernaeopodidea.

·        Phylum Annelida

·        These are  segmented,coelomate worms with a muscular body wall. Important fish parasite under this group is the leech, which may also act as vectors for other pathogens.

·        ClassHirudinea - They have asegmented body round or dorsoventrally flattened with anterior and posteriorsuckers. Leeches are ectoparasitic on fish.

·        Phylum Chordata

·        The lampreys, or cyclostomes,which are eel-like, mostly fresh-water or anadromous, jawless fishes having around suctorial disc-like mouth with horny teeth attach to other animals andact as parasites.

4.1.2 Life cycles of parasitesProtozoa

Most protozoan fish parasiteshave a direct life cycle with no intermediate host.

Myxosporean parsites (Myxobolus cerebralis) and blood-parasitic flagellates and haemogregarines are also considered to have a life cycle with a secondary blood-feeding leech as anintermediate host.

4.1.2.1 Monogenea

Monogenean parasites have a direct life cycles without an intermediate host. Adult parasite lays eggs, which hatch to release free-swimming ciliated larvae known as oncomiracidia. These infect suitable host fish within a few hours. If they cannot find a host they die. The oncomiracidia, which are attached to a suitable host develop into adults. Gyrodactylids are viviparous and give birth to new individuals identical to the parent without ay intermediate host.

4.1.2.2 Digenea

The fish parasitic digeneans are oviparous and the eggs laid by adults hatch to release a small ciliated free-swimming miracidium larva. This are alive for a few hours, bythen if it could locate the first intermediate host of a gastropod or bivalve mollusc, it develops into free swimming cercariae after an asexual reproduction phase. These larvae survive for up to about 24 hours within which it finds a suitable second host. In some cases cercariae penetrate into a fish and mature directly to adult stage. Sometimes fish may act as an intermediate host and the cercariaencysts within the fish to form the metacercarial stage. Metacercariae maysurvive for several years in fish and when another fish or any final host eats this it develops into adult.

4.1.2.3 Cestoda

Cestodes are oviparous and the eggs laid are passed in the faeces of the final host which hatch to release a free-swimming larva, the coracidium. This is eaten by an invertebrate copepod intermediate host. Coracidium develops into procercoid, a stage which can infect the fish. When a suitable secondary host eat the procercoid, it penetrates through the gut wall and encysts in the viscera or musculature where it develops to the plerocercoid stage. When this infected fish is eaten by a final host (fish, a bird or a mammal) the larvae completes the life cycle by becoming an adult.

(diagram)

4.1.2.3 Cestoda

Cestodes are oviparous and the eggs laid are passed in the faeces of the final host which hatch to release a free-swimming larva, the coracidium. This is eaten by an invertebrate copepod intermediate host. Coracidium develops into procercoid, a stage which can infect the fish. When a suitable secondary host eat the procercoid, it penetrates through the gut wall and encysts in the viscera or musculature where it develops to the plerocercoid stage. When this infected fish is eaten by a final host (fish, a bird or a mammal) the larvae completes the life cycle by becoming an adult.

(diagram)

4.1.2.4 Acanthocephala

The Acanthocephalans need one invertebrate host for completing their life cycle. They produce eggs which are passed through the faeces and then hatch into an acanthor larva in the intermediate host. The acanthor larva penetrates into host body cavity and develops into acystacanth which, when eaten by a suitable final host, develops into a mature parasite.

4.1.2.5 Nematoda

Eggs of oviparous nematodes or larvae of viviparous ones released by the host are ingested by an intermediate arthropod host. Further development of the nematode occurs in the intermediate host. The nematode larva penetrates through the gut wall into the viscera and musculature and get encysted. Once the infected fish is eaten by the final host - a fish, bird or mammal, the life cycle of nematodes is completed.

 

4.1.2.6 Mollusca

Larval stage of fresh-water bivalve molluscs is known as glochidia, which are obligatory parasites in fish. The glochidia larva released by the adult mollusc finds a suitable fish host and hold tightly on to the gills, fins or skin. These would later metamorphose to form a free living juvenile mollusc.

 

4.1.2.7 Copepoda

Eggs of parasitic copepods hatch to free- swimming nauplius larvae which moults to copepodid stage. There may be several copepodid stages before getting matured. Adult female copepods attach to the final host. The adult malesare usually non-parasitic.

4.1.2.8 Leeches

Leeches have a direct life cycle. Cocoons laid by adults are attached to a substrate or held by parent hatch to produce young leeches.

 

4.1.2.9 Lampreys

Lampreys spawn in fresh-water and the larvae is known as ammocoete larvae, which are slender and worm-like. These may live fora number of years buried in mud and later metamorphose into the adult stage.The adults die after spawning,

4.1.2.9 Lampreys

Lampreys spawn in fresh-water and the larvae is known as ammocoete larvae, which are slender and worm-like. These may live fora number of years buried in mud and later metamorphose into the adult stage.The adults die after spawning.

Protozoan parasitic fish diseases :

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