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[[File:Sea lice on salmon.jpg|thumb|200px|right|Sea lice on a salmon. (Wikimedia Commons)]]

[[File:Sea lice on salmon.jpg|thumb|200px|right|Sea lice on a salmon. (Wikimedia Commons)]]

Sea lice are '''parasites of the Caligidae family of arthropods''' and are among the most '''notorious pests''' affecting cultured marine fish. They have a particularly large impact upon salmonid fish production. The parasites '''feed on blood''' from their hosts, causing significant superficial damage and consequent impact upon circulatory volume.  

Sea lice are '''parasites of the Caligidae family of arthropods''' and are among the most '''notorious pests''' affecting cultured marine fish. They have a particularly large impact upon salmonid fish production. The parasites '''feed on body mucus, epidermal tissues and blood''' from their hosts, causing significant superficial damage and consequent impact upon circulatory volume.  

The lice are brown-red in colour, have 5 pairs of legs and the female is considerably larger than the male (10mm and 6mm respectively) with a long egg sac. Three leg pairs are for swimming and the other two adapted for eating.  

The lice are brown-red in colour, have 5 pairs of legs and the female is considerably larger than the male (10mm and 6mm respectively) with a long egg sac. Three leg pairs are for swimming and the other two adapted for eating.  

==Lifecycle==

==Lifecycle==

Eggs are released into the environment from long egg sacs. There are then '''two non-parasitic larval stages'''. Larval migration may exceed 1km.

Eggs are released into the aquatic environment from long egg sacs. There are '''two non-parasitic larval stages''' that include copepod, chalimus and pre-adult. Larval migration may exceed 1km and they may be carriers of bacteria and viruses as they migrate from fish to fish.

'''Seven parasitic larval stages follow including copepod, chalimus and pre-adult'''. The larvae damage the fish’ skin by penetrating the epidermis an dermis with first their antennae followed by their cephalothoracic shield which causes separation from the basement membrane. They then secrete a substance which hardens to form their frontal filament and moult into the '''first chalimus''' stage.<ref>Bron, J. E., Sommerville, C., Jones, M., Rae, G. H (1991) '''The settlement and attachment of early stages of the salmon louse, Lepeophtheirus salmonis (Copepoda: Caligidae) on the salmon host, Salmo salar.''' ''J Zoology'', 224:201-212</ref>

'''Seven parasitic larval stages follow including copepod, chalimus and pre-adult'''. The larvae damage the fish’ skin by penetrating the epidermis an dermis with first their antennae followed by their cephalothoracic shield which causes separation from the basement membrane. They then secrete a substance which hardens to form their frontal filament and moult into the '''first chalimus''' stage.<ref>Bron, J. E., Sommerville, C., Jones, M., Rae, G. H (1991) '''The settlement and attachment of early stages of the salmon louse, Lepeophtheirus salmonis (Copepoda: Caligidae) on the salmon host, Salmo salar.''' ''J Zoology'', 224:201-212</ref>

''L. salmonis'' is the exception, affecting '''Atlantic salmon in the colder waters''' of the Northern hemisphere. It also infects salmonids is Japan.

''L. salmonis'' is the exception, affecting '''Atlantic salmon in the colder waters''' of the Northern hemisphere. It also infects salmonids is Japan.

''C. orientalis'' is also found in '''Japan''' in rainbow trout. ''C. elongatus'' is the most common species in '''British waters''', ''C. teres'' and ''C. rogercresseyi'' in '''Chile''', ''C. epidemicus, C. punctatus'' and ''C. orientalis'' in '''Asia''' and ''L. pectoralis'' occurs in the north-east '''Atlantic Ocean, Balic Sea and White Sea'''.

''C. orientalis'' is also found on rainbow trout in '''Japan'''. ''C. elongatus'' is the most common species in '''British waters''', ''C. teres'' and ''C. rogercresseyi'' in '''Chile''', ''C. epidemicus, C. punctatus'' and ''C. orientalis'' in '''Asia''' and ''L. pectoralis'' occurs in the north-east '''Atlantic Ocean, Balic Sea and White Sea'''.

No significant problems appear to occur in the Southern hemisphere except for ''C. elongatus'' in '''Australia''' which originated from wild fish and is thought to have been introduced by ballast water translocated from northern Asia.

No significant problems appear to occur in the Southern hemisphere except for ''C. elongatus'' in '''Australia''' which originated from wild fish and is thought to have been introduced by ballast water translocated from northern Asia.

==Treatment==

==Treatment==

'''[[Ectoparasiticides]]''' are available in a variety of formulations but '''not all are approved for food fish''' so care should be taken when selecting. Resistance is also an issue.

'''[[Ectoparasiticides]] (e.g. organophosphates, pyrethroids, hydrogen peroxide) ''' are available in a variety of formulations but '''not all are approved for food fish''' so care should be taken when selecting. Resistance is also an issue.

 

In-feed treatments include coating the feed with drugs (e.g. avermectins) or with growth inhibitors (e.g. Teflubenzuron).

==Control==

==Control==

'''[[Ectoparasiticides]]''' can also be used prophylactically.

'''[[Ectoparasiticides]]''' can also be used prophylactically.

'''Biological control''' has also been investigated, in a search for feeder species such as '''wrasse''' which may decrease louse numbers.  

'''Biological control''' has also been investigated, in a search for feeder species such as '''wrasse''' (natural predator) which may decrease louse numbers.  

Management improvements are imperative, and an '''all-in-all-out system''' is ideal.

Management improvements are imperative, and an '''all-in-all-out system''' is ideal.

'''Selective breeding''' from resistant breeds is also advised but difficult.

'''Selective breeding''' from resistant breeds is also advised but difficult.

{{Learning

{{Learning

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|date =11 July 2011

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[[Category:Fish Diseases]]

[[Category:Fish Diseases]]

[[Category:Crustacea]]

[[Category:Crustacea]]

[[Category:CABI Expert Review]]

[[Category:CABI Expert Review]]