Effect of environmental salinity on sea lice Lepeophtheirus salmonis settlement success

Ian R. Bricknell*, Sarah J. Dalesman, Bríd O'Shea, Campbell C. Pert, A. Jennifer Mordue Luntz

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

157 Citations (SciVal)

Abstract

The sea louse Lepeophtheirus salmonis (Krayer, 1837) (Copepoda: Caligidae) is an ectoparasite of salmonid fish. It has earlier been proposed that the free-swimming infectious copepodid stage of L. salmonis gather at river mouths to infect wild Atlantic salmon Salmo salar L. and sea trout S. trutta L. smolts during their seaward migration. This study used aquarium-based methods to investigate the survival, infective ability and behaviour of L. salmonis copepodids exposed to short periods of low salinity levels, such as those encountered at river mouths. Survival of free-swimming copepodids was found to be severely compromised at salinity levels below 29 parts per thousand (ppt). Attachment to an S. salar host did not aid copepodid survival during post-infection exposure to low salinity environment, and a reduction in salinity appears to reduce the ability of copepodids to remain attached to S. salar smolts. Pre-infection exposure of copepodids to reduced salinity levels reduced infection of S. salar. Infection levels at reduced salinity were lower than predicted from the free-swimming survival experiment, suggesting that low salinity compromises the copepodids' ability to sense or respond to the presence of a host. In salinity gradients, copepodids demonstrated avoidance of salinities below 27 ppt, by both altering their swimming behaviour and changing the orientation of passive sinking. Avoidance of low salinity levels may be due to their adverse effects on copepodid physiology, as suggested by the reduction in survival. Sinking rates were also faster in reduced salinity, suggesting that remaining in the water column would be more energetically demanding for the copepodids at reduced salinity. These results show that both survival and host infectivity of L. salmonis are severely compromised by short-term exposure to reduced salinity levels.

Original languageEnglish
Pages (from-to)201-212
Number of pages12
JournalDiseases of Aquatic Organisms
Volume71
Issue number3
DOIs
Publication statusPublished - 30 Aug 2006

Keywords

  • Hyposalinity
  • Infection rate
  • Salinity gradients
  • Sea lice
  • Survival

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