Sea Lice

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Sea Lice - Copyright Joseph G. Kunkel at The Kunkel Fish & Aquatic Invert Site

• Economic importance to the fish farming industries
  • Especially in North American and in Northern Europe

• Lepeophtheirus is found only in the Northern hemisphere

• Caligus is found worldwide

Recognition

• Males measure 6mm in length

• Females measure 1cm long
  • Have a long egg sac

• 5 pairs of legs
  • 3 pairs for swimming
  • 2 pairs modified for eating

• Brown to red in colour

• Similar in appearance to the horse shoe crab

Life Cycle

• Eggs released from long egg sacs into environment

• 2 non-parasitic larval stages

• 7 parasitic larval stages (nauplius)
  • Copepod, chalimus and pre-adult

• Life cycle takes 3 weeks to 4 months depending on temperature

Epidemiology

• Largely found in salt water

• Most wild salmonids migrate to the sea for part of their life cycle

• Sealice numbers are low on wild salmonids (adults only)

• Sealice numbers are high on farmed salmonids (larvae and adults)
  • 90% prevalence
  • Average of 5-10 sealice upon a single fish
  • Most sealice found on dorsal fin, head and back and underside of tail and fins
  • Adults survive for over 3 weeks
  • Migration of larval stages can be up to 1km
  • Larvae locate host by responding to changes in light and vibration

Pathogenesis

• Adults and larval stages are epidermal browsers

• Mouth tube of toothed ridges abrades fish epidermis

• Heavy infections leads to:
  • Epidermal abrasion
  • Haemorrhage
  • Immunosuppression
  • Decreased productivity
  • Death

Control

• Ectoparasiticides

• Hidden antigen vaccine

• Wrasse which feed on sealice

• Management improvements
  • E.g. All in, all out and 6 week fallowing

• Stock selection
  • e.g. Selective breeding for resistance