Presentation: State-of-Knowledge Initiative for the Special Committee on Sustainable Aquaculture of the British Columbia Legislature

Delivered November, 2006.

Return to Presentation Index.

Biology of Sea Lice

[A full pdf copy for printing may be downloaded from the WAVES database.]

The sea lice species Lepeophtheirus salmonis and Caligus clemensi are common parasites of salmonids and other fishes in coastal British Columbia. Free-living planktonic and parasitic stages occur during the development of both species¹⁶.

The distribution, developmental rate and survival of the free-living planktonic larvae are influenced by the movement, temperature and salinity of the seawater in which they are found1,2,14. Time to hatching and development of L. salmonis eggs and larvae is increased in colder water.

This means that at a temperature of 10ºC, larval L. salmonis are infective to fish between 4 and 10 days from the time of hatching^19,21. The development of L. salmonis to sexual maturity following attachment to the fish host also depends on temperature and the generation time, from egg to mature adult, ranges from 32 days at 14-15ºC to 106 days at 7.5ºC4,20.

There is evidence that L. salmonis matures more slowly on coho salmon than on Atlantic salmon or rainbow trout⁶, indicating that the host environment also influences parasite development.

The survival, planktonic development, settlement on the host and development on the host fish are adversely affected by low salinity. Low salinities appear to have a greater impact on the planktonic than on the parasitic stages16. Newly hatched larvae do not survive below 15 parts per thousand (‰) and only negligible development to the infective copepodid occurs between 20 and 25‰ (salinity of the open oceans varies from 33 to 38‰).

A recent study showed the survival of free-swimming copepodids was “severely compromised” by salinities below 29‰³. The adverse effects of low salinities on planktonic stages probably explain the consistently low abundances of L. salmonis and C. clemensi on naturally infected salmon and sticklebacks collected from low salinity areas within the Broughton Archipelago^11,12.

Most of the research exploring the effects of low salinity on L. salmonis was conducted in Europe^3,7,17. Some recent studies have begun to study this aspect of sea lice ecology on British Columbia, but more data are required^4,12.

The behaviour of planktonic sea lice larvae includes active mobility and several adaptations to enhance host finding and attachment. The infective copepodid responds to light, chemical gradients, and mechanical stimuli (pressure waves)^5,7,8,9.

Copepodids of L. salmonis display diurnal (daily) patterns of vertical motility in the water column that may increase the opportunity for interaction with hosts (attracted to surface during day light)¹⁶. The importance of effective host-finding mechanisms reflects the limited survival of the non-feeding planktonic larvae, whose energy is provided by stored lipid¹.

Lepeophtheirus salmonis, although commonly referred to as the salmon louse, is known to infest several non-salmonid species, including saithe (Pollachius virens), and sea bass (Dicentrarchus labrax) in Scotland and three spine sticklebacks in British Columbia11,^13,15. Gravid females have been reported from the sea bass and saithe, whereas the parasite develops only to the preadult stage on the stickleback¹¹.

While more research is required to understand the significance of L. salmonis infections on non-salmonid hosts, an earlier study confirmed the ability of motile L. salmonis stages to move between hosts¹⁷

References

1. Boxaspen K. 2006. A review of the biology and genetics of sea lice. ICES J. Mar. Sci. 63: 1304-1316.

2. Boxaspen K, Naess T. 2000. Development of eggs and the planktonic stages of salmon lice (Lepeophtheirus
    salmonis) at low temperatures. Contr. Zool. 69: 51-55.

3. Bricknell IR, Dalesman SJ, O’Shea B, Pert CC, Mordue Luntz AJ. 2006. Effect of environmental salinity on sea
    lice Lepeophtheirus salmonis settlement success. Dis. Aquat. Org. 71: 201-212.

4. Brooks KM. 2005. The effects of water temperature, salinity and currents on the survival and distribution of
    the infective copepodid stage of sea lice (Lepeophtheirus salmonis) originating on Atlantic salmon farms in
    the Broughton Archipelago of British Columbia, Canada. Rev. Fish. Sci. 13: 177-204.

5. Browman HI, Boxaspen K, Kuhn P. 2004. The effect of light on the settlement of the salmon louse,
    Lepeophtheirus salmonis, on Atlantic salmon, Salmo salar L. J. Fish Dis. 27: 701-708.

6. Fast MD, Ross NW, Mustafa A, Sims DE, Johnson SC, Conboy GA, Speare DJ, Johnosn G, Burka JF. 2002.
    Susceptibility of rainbow trout Oncorhynchus mykiss, Atlantic salmon Salmo salar and coho salmon
    Oncorhynchus kisutch to experimental infection with sea lice Lepeophtheirus salmonis. Dis. Aquat. Org. 52:
    57-68.

7. Genna RL, Mordue W, Pike AW, Mordue (Luntz) AJ. 2005. Light intensity, salinity, and host velocity influence
    presettlement intensity and distribution on hosts by copepodids of sea lice, Lepeophtheirus salmonis. Can. 
    J. Fish. Aquat. Sci. 62: 2675-2682.

8. Hevrøy EM, Boxaspen K, Opedal F, Taranger GL, Holm JC. 2003. The effect of artificial light treatment and
    depth on the infestation of the sea louse Lepeophtheirus salmonis on Atlantic salmon (Salmo salar L.)      
    culture. Aquaculture 220: 1-14.

9. Ingvarsdottir A, Birkett MA, Duce I, Genna R, Mordue W, Pickett JA, Wadhams LJ, Mordue (Luntz) AJ 2002.
    Semiochemical strategies for sea louse control: host location cues. Pest Manag. Sci. 58: 537-545.

10. Johnson SC, Albright LJ. 1991. Development, growth and survival of Lepeophtheirus salmonis (Copepoda:
    Caligidae) under laboratory conditions. J. Mar. Biol. Assoc. UK. 71: 425-436.

11. Jones SRM, Prosperi-Porta G, Kim E, Callow P, Hargreaves NB. 2006. The occurrence of Lepeophtheirus
    salmonis and Caligus clemensi (Copepoda: Caligidae) on threespine stickleback Gasterosteus aculeatus in
    coastal British Columbia. J. Parasitol. 92: 473-480.

12. Jones SRM, Wosniok W, Hargreaves NB. 2006. The salmon louse on salmonid and non-salmonid fishes in
    British Columbia. Proc. 11th ISVEE. 1131
    (http://www.sciquest.org.nz/default.asp?pageid=69&pub=10&vol=11)

13. Lyndon AR, Toovey JPG. 2001. Occurrence of gravid salmon lice (Lepeophtheirus salmonis (Kroyer)) on
    saithe (Pollachius virens (L.)) from salmon farm cages. Bull Eur Assoc Fish Pathol 21: 84-85.

14. Pacific Salmon Forum. Protocols and Guidelines for Sea Lice Research. SPG1.
http://www.pacificsalmonforum.ca//pdfs-all-docs/PGs.pdf.

15. Pert CC, Urquhart K, Bricknell IR. 2006. The sea bass (Dicentrarchus labrax L.): a peripatetic host of
    Lepeophtheirus salmonis (Copepoda: Caligidae). Bull. Eur. Assoc. Fish Pathol. 26: 163-165.

16. Pike AW, Wadsworth. SL. 1999. Sea lice on salmonids: their biology and control. Adv. Parasitol. 44: 233-
    337.

17. Ritchie G. 1997. The host transfer ability of  ;Lepeophtheirus salmonis (Copepods: Caligidae) from farmed
    Atlantic salmon. J. Fish Dis. 20: 153-157.

18. Tucker CS, Sommerville C, Wootten R. 2000. The effect of temperature and salinity on the settlement and
    survival of copepodids of Lepeophtheirus salmonis (Krøyer, 1837) on Atlantic salmon, Salmo salar L. J. Fish
    Dis. 23: 309-320.

19. Tucker CS, Sommerville C, Wootten R. 2000. An investigation into the larval energetics and settlement of
    the sea louse, Lepeophtheirus salmonis, an ectoparasitic copepod of Atlantic salmon, Salmo salar. Fish
    Pathol. 35: 137-143.

20. Tully O. 1992. Predicting infestation parameters and impacts of caligid copepods in wild and cultured fish
    populations. Invert. Reprod. Devel. 22: 91-102.

21. Wootten R, Smith JW, Needham EA. 1982. Aspects of the biology of the parasitic copepods Lepeophtheirus
    salmonis and Caligus elongatus on farmed salmonids and their treatment. Proc. Roy. Soc. Edinburgh 81B:   
    185-197.