Are viruses keeping sea lice at bay in wild salmon?

June 22, 2023

Sea lice on a juvenile salmon. Hakai Institute.

More than 30 previously unknown RNA viruses in sea lice have been identified by University of British Columbia (UBC) researchers. Sea lice are parasitic copepods (small crustaceans) found in many fresh and saltwater habitats, and have been implicated in the decline of wild salmon populations. The research sheds greater light on the types of viruses being carried by sea lice, and how the viruses and host are interacting.

“We found many more types of viruses than are known in sea lice or their distant relatives; the lice are mounting an immune defense response to many of these viruses indicating that they are replicating,” says UBC marine microbiologist Dr. Curtis Suttle, senior author of the paper published this week in PLOS Pathogens.

As part of his PhD research with Dr. Suttle’s group, co-author Dr. Tianyi Chang analyzed RNA from three species of sea lice (Lepeophtheirus salmonis, Caligus clemensi and Caligus rogercresseyi) that have a large ecological and economic impact on fish and fisheries. The data were obtained from sea lice removed from out-migrating juvenile salmon collected in the waters surrounding the Discovery Islands and Broughton Archipelago on the northeastern side of Vancouver Island, as well as from farmed salmon in Chile.

Sea lice are a big problem for the fish aquaculture industry worldwide due to their proliferation among dense populations of farmed fish. Chemical treatments have failed to solve the problem.

Viruses tend to kill species that flourish, so populations that might otherwise take over an ecosystem are often controlled by viruses. By infecting and weakening their hosts, viruses maintain balance in nature.

“In a natural system, viruses may prevent explosions in sea-lice populations by rapidly replicating when densities become high, and so might form a natural biological control agent for a parasite of salmon,” says Dr. Suttle.

The viruses encompassed all the major groups of RNA viruses, with many likely representing new families and genera. Surprisingly, the closest relatives of some of the newly discovered viruses are only known to infect plants or fungi. This implies that over evolutionary time, viruses jumped between fungi and arthropods, a group of animals that includes crustaceans such as sea lice and crabs, as well as spiders and insects, the researchers said.


For more information, contact…

UBC Public Affairs

  • Bacteria + Viruses
  • Earth, Ocean and Atmospheric

Musqueam First Nation land acknowledegement

UBC Science acknowledges that the UBC Point Grey campus is situated on the traditional, ancestral, and unceded territory of the xʷməθkʷəy̓əm.

Learn more: Musqueam First Nation

Faculty of Science

Office of the Dean, Earth Sciences Building
2178–2207 Main Mall
Vancouver, BC Canada
V6T 1Z4
UBC Crest The official logo of the University of British Columbia. Urgent Message An exclamation mark in a speech bubble. Arrow An arrow indicating direction. Arrow in Circle An arrow indicating direction. A bookmark An ribbon to indicate a special marker. Calendar A calendar. Caret An arrowhead indicating direction. Time A clock. Chats Two speech clouds. External link An arrow pointing up and to the right. Facebook The logo for the Facebook social media service. A Facemask The medical facemask. Information The letter 'i' in a circle. Instagram The logo for the Instagram social media service. Linkedin The logo for the LinkedIn social media service. Lock, closed A closed padlock. Lock, open An open padlock. Location Pin A map location pin. Mail An envelope. Mask A protective face mask. Menu Three horizontal lines indicating a menu. Minus A minus sign. Money A money bill. Telephone An antique telephone. Plus A plus symbol indicating more or the ability to add. RSS Curved lines indicating information transfer. Search A magnifying glass. Arrow indicating share action A directional arrow. Twitter The logo for the Twitter social media service. Youtube The logo for the YouTube video sharing service.