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.