Parasitic diseases of fish

Different parasitic diseases in fish

1. PARASITIC DISEASES OF FISH :
PRESENTED BY:
Avijit pramanik
AAH-MA-09-02
B.F.Sc, W.B.U.A.F.S.
M.F.Sc, CIFE, MUMBAI

2. Host
Host-Parasite-Environment Relationship
(Sniezko, 1974)
Pathogen
Environment
Disease

3. GENERAL PARASITOLOGY
•Decreased growth rate and emaciation.
•Decreased host fecundity.
•Decreased host’s survival.
•Secondary infections…
•Vectors of bacteria, virus or parasitic
protozoa.

4. Specimen collection:
•The Best: Wet mounts of live preparations
(live or recently euthanatized fish).
•Preservative: 10% BNF or 70% Ethanol.
•Refrigeration or stored on ice for up to 24
hours.
•Freezing.

5. Parasitological Examination
•Methodical examination of the fins, body,
buccal cavity and gills.
•Remove large ectoparasites.
•Skin and mucus samples.
•Gill sample.
•Blood sample.
•Internal organ’s examination : Wet Mount,
Histology, Cytology.

6. Protozoan fish parasites
•Cause more disease in cultured fish farm than any
other parasite group.
•Intensive aquaculture system can cause serious
morbidity and mortality.
•GROUPS : Sarcomastigophora, Ciliophora,
Apicomplexa, Microspora and Myxospora.

7. Sarcomastigophoran Protozoa
•Flagella and /or pseudopodia.
•Asexual reproduction by binary fission.
•Life cycle: Direct (Ichtyobodo) or Indirect
(Trypanosoma).
•Mucosal surfaces (skin, gills, intestinal tract) or
blood.

8. Ciliated Protozoa
•Presence of 2 or more nuclei.
•Ingest nutrients through a cytostome -
cytopharynx that may be surrounded by cilia.
•Reproduction : Usually by binary or multiple
fission.
•Mobile or sessile.
•E.g.: Trichodina, Schyphydia, Tetrahymena,
Ichtyophthirius, Chilodonella, etc.

9. Ciliated protozoa

10. Epistylis sp. ( Peritricha)
Cluster of Epistylis on
body surface of fish.
Epistylis sp., SEM

11. Lyfe Cycle of Ichthyophthirius multifilis

12. Apicomplexa
•Apical complex used to penetrate the host
cell.
•Parasitic, mostly intracellular.
•Coccidia and Piraplasma
•Transmission is almost always direct.
•Usually asymptomatic, but extraintestinal
infection can cause morbidity and mortality
•Diagnosis: Spore morphology

13. Microspora
•Classification is based upon the life cycle, type of
sporogony and spore morphology.
•Xenoma: whitish, cyst like, mm cm
•Spores very resistant to environmental conditions
•Glugea, Pleistophora
Spore Host Sporoplasm Meronts
Sporogony Sporonts

14. MYXOZOA
•Restricted to invertebrates and poikilothermic
vertebrates.
•Obligate parasites of tissues and organ cavities.
•Multinucleated forms that are primary cells
containing enveloped secondary cells.
•Direct or indirect life cycle (invertebrate
intermediate host)
•Young fish!!
•Classification: Spore structure

15. Spores of Myxobolus cerebralis

16. Mature Henneguya cysts within the gill lamellae.

17. METAZOA
•Monogenetic Trematodes
•Digenetic Trematodes
•Cestodes
•Nematodes
•Acanthocephalans
•Molluscs
•Leeches
•Crustacea: Copepods, Branchiura, Isopods
•Lampreys

18. Monogenetic Trematodes
•Body, fins, gills, and /or oral cavity, epithelium
or blood.
•Dactylogyrus, Acolopenteron, Enterogyrus,
Gyrodactylus, etc.
•Most are highly host and site specific.
•Direct life cycle.
•Most are oviparous. Gyrodactylus is viviparous.
•Taxonomy: Morphology of posterior
attachment organ; quantity of oral suckers,
pigmented eye spots, etc.

19. Monogenean Fish Parasites: Dactylogyrus spp.
and Gyrodactylus spp.

20. . Gyrodactylus olsoni on the gill filament
of longjaw mudsucker (SEM).
•b - attachment organ
a - general view
c - anchors and
marginal hooks of the
attachment organ.
b - attachment
organ.

21. Monogenetic Trematodes
•Morbidity and mortality in stressful conditions.
•Dactylogyrids: Primarily gill parasites of
freshwater fish.
•Gyrodactylids: Skin and gill parasites of both
freshwater and marine fish.
•Lesions due to feeding activity of the parasites
as well as to the mechanical damage due to the
anchors and hooklets of the opisthaptor.
•Hemorrhage and hyperplasia of gill lamellae,
secondary bacterial and protozoal infections.

22. Digenetic Trematodes
•Very large group of endoparasites that have
indirect and often complex life cycles.
•Monoecious and oviparous
•Larval digeneans can be found in almost any
fish tissue and may as adults parasitize a wide
variety of carnivorous hosts (fish, mammals
and birds).
•Metacercaria: “white grubs”, “black spot
disease”
•Diplostomum, Centrocestus, Ascocotyle,
Sanguinicola, Tetracotyle, etc

23. Visible white or yellow spots in the visceral organs, usually about
1 mm in diameter are referred as “white grubs” or “yellow grubs”.

Fig. Showing white grub

24. Representative life cycles of digenetic
trematodes

25. Cestodes
•Tapeworms may occur in fish as sexually mature
adults (intestine and pyloric ceca) or as larval
forms (plerocercoids) in the abdominal cavity,
visceral organs and/or musculature.
•Life cycle: 1-2 intermediate hosts. Fish as IH or
DH.
•Eucestoda and Cestodaria - scolex.
•Oviparous
•Heavy adult infestations: Retard growth rate,
hemorrhagic enteritis.
•Larval infestation : Migrating larva cause damage
to organs. In musculature - esthetically
undesirable fillet.

26. Representative life cycles of Cestodes

27. Heterophid life cycle

28. Nematodes
•Bilaterally symmetrical organisms that have a
pseudocoelom and a gut.
•Cylindrical and posses a complete digestive
tract.
•Larval and adult forms in freshwater and
marine fishes.
•Most adult nematodes occur in the stomach
and intestine. Some are extraintestinal.
•Damage to the visceral organs and other tissues
during migration through the fish host.
•Philonema, Contracaecum, Anisakis, Spiroxys,
Eustrongylides, Capillaria, Camallanus,etc.

29. Nematodes
•Identification: External and internal
anatomic structures; egg morphology.
•Separate sexes, mostly oviparous with
free swimming larvae.
•Fish, Invertebrate, Carnivorous
•Pathology: Inflammation and ulceration
of the gut of fish , emaciation. Migrating
larva!!

30. Representative life cycles of Nematodes

31. Contracaecum spp. life cycle

32. Parasitic Crustacea

33. Parasitic Crustaceans
•Complete digestive system.
•Dioecious, females larger than males.
•Classification: Body form, segmentation,
limbs, form of attachment pouch,
morphology of egg sac or brood sac.
•Copepods, Branchiura, Isopods.

34. Copepods
•Important both as parasites of fish and intermediate
hosts for other fish parasites.
•2 main body divisions: cephalothorax and abdomen.
•Ergasilus spp: Gills or buccal cavity.
•Lernaea spp.: Freshwater and marine species. Mainly
in skin, attached in the musculature.
•Localized inflammation and ulceration of the area of
attachment. Secondary infections. Massive copepod
infestation can cause severe pathology.

35. Branchiura
•“Fish lice” - Obligate ectoparasites of the skin and
rarely the buccal cavity of freshwater and marine fishes.
•Argulus spp.
•Periodic parasites of fish, very little host specificity.
Among IMCs mostly infest Rohu.
•Simple development: Juveniles are similar in
morphology to adults.
•Damage: Repeated piercing of the skin by the preoral
sting, which injects a toxic substance into the
underlying epidermis.

36. Isopod Parasites
•Isopods occur very commonly as parasites of food fishes.
•There are about 430 isopod species parasitic on fish.
•Isopods belonging to the “Cymothoid” type attach to fish early in
life and pass through the male stage before becoming female.
•The Gnathiid isopods are parasitic only during the larval stage,
known as praniza.
•Male isopods are only facultatively parasitic, capable of leading
either free or parasitic existence.
•Isopod parasites are usually large and fierce looking and the damage
they cause to the host fish is considerable.
•They produce gall-like depression in the skin and muscles of the body
wall.
•Isopods attack fishes of marine, brackish and freshwater habitats.