Fish louse (<i>Argulus</i> infestation)


Epidermal hyperplasia
Excessive growth on skin.
Visible crustaceans
It is easily possible to see the small "crab-like" parasites on the body.
Skin lesions
Lots of small lesions appear on the skin
Small circular wounds
Small circular wounds on skin.
Ulcers - circular
Ulcer with circular shape.
Haemorrhages - skin
Bloody haemorrhages are apparent over several parts of the skin.
Red necrotic lesions - skin
The skin shows red necrotic lesions.
Reddish inflammation
Around the wound caused by the parasite, there is a bloody inflamed area
Fish is fading away, looks as if it is starving to death.
Reluctant to feed
Fish comes to eat but with evident lack of appetite.
Fish constantly rubs or scratches itself against any object available.
Very agitated
Fish rushes around the tank or pond in an abnormal manner.


Argulus popularly known as " fish louse" is an ectoparasite belonging to the crustacean group. This parasite belongs to the Branchiura group and is normally introduced by live food or new pond-reared fish. Parasite is prevalent in many outside ponds and will cause severe damage to body if left unchecked.
Most freshwater species are affected, with especial emphasis on the following families. Bowfins, Carp, Drums, Killifish, Perch, Pikes, Sticklebacks, Sturgeons, Sunfishes, & Basses.
Argulus feeds on host tissue by sucking action of its mouth . The parasite can transmit SVC( Spring Viremia of Carp).


Parasites can be eradicted without too much trouble. Care should be taken to see that all parasites have been eliminated after treatment.

May cause heavy mortality in small fish.


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Try to ensure tanks or ponds are free of parasites before introducing fish, by "sterilizing" them according to good Aquacultural practise.

DNA and RNA diagnostic references

Molecular characterization of Argulus bengalensis and Argulus siamensis  (Crustacea: Argulidae) infecting the cultured carps in West Bengal, India using 18 rRNA gene sequences. 

From Mol.Biol. Res. Commun. 2016 Sept. Avijit Patra et al. 


Dr. Chacko, Jim
Unity College of Maine
Fish Patholgy Dept.


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