VPP 322: Aquatic Animal Diseases, Health Care and Management (1+1)

PARASITIC DISEASES

• Parasites are classified into two broad groups
  • Ectoparasites which are found on the external surfaces such as skin, fins and gills.
  • Endoparasites which are found in the internal tissues and organs.
• Many parasites require an intermediate host, such as snails, birds or the introduction of an infected fish, and so are rare in pond/aquarium fish. There are a variety of clinical signs which might indicate the presence of endoparasites. Lethargy accompanied by emaciation is a common sign, as are worms protruding from the anus. Identification of sporozoan and protozoan endoparasites often requires microscope examination of tissues.
• Ectoparasites can cause severe damage to the skin from their feeding activities and /or their constant movement and attachment structure such as hooks and suckers. This is turn can often lead to
  • Secondary bacterial infections, typically ulcers and bacterial gill disease.
  • Excess mucus production, seen as grey, slime film and epithelial hyperplasia, causing respiratory problems if the gills are affected.
• Larger parasites infecting fishes include leeches, lice and anchor worms. These are visible with the naked eye. Typical signs of parasite infestations are rubbing on hard subtrates, focal redness and inflammation at the base of the dorsal fin, bulged operculum, and lethargy.

Fish infested with Argulus sp

View video....

Parasitic disease	Causative agent	Symptoms
Monogenean trematodiasis   Digenean trematodiasis	Gyrodactylus sp. and Dactylogyrus sp. Gyrodactylus sp. has a V-shaped head, no eyespots and is viviparous (live-bearing). Dactylogyrus sp. has a scalloped head, distinct eyespots and is oviparous (egg-laying)   Posthodiplostonum and Clinostonum sp.	Commonly invade the gills, skin and fins of fish. They are found externally or internally in any organs. Increased melanin deposition “black spot disease”.
Nematodes - Round worms	Camillanus, Capillaria and Eustrongylides	Infect all organs of the host, causing loss of function of the organs, results in stunted growth, abnormal swimming, lethargy or death.
Leeches - Annelid worms	Piscicola and Cystobranchus.	Parasitic on host’s blood chronic anemia, develop secondary bacterial and fungal infections at the attachment site.
Lernaeasis (Crustaceans)	Lernaea sp.  is commonly called as anchor worm	Heavy infections lead to secondary bacterial or fungal infections. Loss of physical condition and weakening of the host and death in some cases
Argulosis (Crustaceans)	Argulus sp. is commonly called as fish lice	Attaches to the external surface of the host and can be easily seen with the naked eye. Feeds on blood which results in anaemic condition in fish