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[[File:Argulus.jpg|250px|thumb|right|'''Fish Louse (''Argulus sp.'') attached to the skin of a fish (Wikimedia Commons)''']]
[[File:Argulus.jpg|250px|thumb|right|'''Fish Louse (''Argulus sp.'') attached to the skin of a fish (Wikimedia Commons)''']]
The '''fish louse''' is a '''metazoan parasite''' of '''freshwater fish'''.
The '''fish louse''' is a '''metazoan [[Crustacea|crustacean]] skin parasites''' of '''freshwater fish'''. They pose a major threat to teh health of commercially produced fish.
The louse has a sharp stylet along the ventral midline that it uses to pierce the skin of the fish. It then injects digestive
==Life Cycle==
The parasite's life cycle is direct. The lice mate on the fish and the female then lays her eggs on surfaces or plants within the habitat. These then progress through a series of stages.
After 4 days the hatched crustacean will seek out a host fish to feed on.
The total life cycle takes 30-100 days and is temperature dependent. Eggs can undergo latency and delayed hatching if water temperatures are not suitable over Winter.
==Pathology and Clinical Signs==
The louse has a sharp stylet along the ventral midline that it uses to pierce the skin of the fish. It then '''injects digestive enzymes''' into the surrounding tissues and feeds on the digested bodily fluids by sucking them out with its '''proboscis'''.
The damage caused by the fish louse is two-fold; firstly '''localised inflammation and irritation''' of the skin caused directly by the parasite and secondarily the risk of developing'''opportunistic infections''', both '''bacterial and viral''' directly through the damaged skin. [[Pseudomonas species - Overview|''Pseudomonas spp.'']] and [[Aeromonas species - Overview|''Aeromonas spp.'']] are often of particular concern, as they can potentially invade the [[Gills|gills]].
Fish may show '''rubbing and flashing behaviour''' due to the intense irritation caused by the infection.
==Diagnosis==
==Diagnosis==
The louse can be seen with the '''naked eye''', growing up to '''7 mm''' in length.
The louse can be seen with the '''naked eye''', growing up to '''7-10 mm''' in length. They appear as flat, oval, darkly coloured spots on the skin of the fish and are easier to see on fins or when moving. Red lesions may be visible from previous feeding areas.
==Treatment==
==Treatment==
Infestations can be treated with an '''increase in water salinity'''. If this is ineffective '''organophosphates''' or '''chitin inhibitors''' can be used.
It is vital that any treatment plan is effective against both adults and juvenile stages of the parasite.
Infestations can be treated with an '''increase in water salinity'''. If this is ineffective, [[Ectoparasiticides|ectoparasiticides]] such as '''organophosphates''' or [[Ectoparasiticides#Modes of Action|'''chitin inhibitors''']] can be used. Three treatments of OPs are usually required to eliminate all life stages. It should be noted that organophosphate treatment is not permitted in the UK and should be confirmed in any other region before use.
{{Learning
{{Learning
==References==
==References==
Aquatic Community '''Argulus''' at http://www.aquaticcommunity.com/disease/argulus.php, accessed online 22/11/2011
Fishdoc '''Argulus/Fish Louse''' at http://www.fishdoc.co.uk/disease/argulus.htm, accessed online 22/11/2011
Frye, FL & Williams, DL (1995) '''Self-Assessment Colour Review - Reptiles & Amphibians''' ''Manson''
Frye, FL & Williams, DL (1995) '''Self-Assessment Colour Review - Reptiles & Amphibians''' ''Manson''
Wildgoose, W (1998) '''Skin disease in ornammental fish: identifying common problems''' ''In Practice 1998 20: 226-243''
Wildgoose, W (1998) '''Skin disease in ornammental fish: identifying common problems''' ''In Practice 1998 20: 226-243''
[[Category:To Do - Manson review]]
[[Category:To Do - Manson review]]
[[Category:Crustacea]]