The study investigated the chemicals released by Atlantic salmon that attract sea lice.
Photo: Helge Skodvin / Nofima.
New research has provided insights into why salmon are particularly susceptible to sea lice infestations, revealing the role of chemical signals in the interaction between salmon and these parasites.
The study, conducted as part of the international CrispResist project, identified chemical compounds released by Atlantic salmon that attract sea lice, as well as potential deterrent substances.
The research indicates that chemical signals, known as semiochemicals, are critical for sea lice to locate their salmon hosts. Specifically, a type of semiochemical called kairomones appears to guide free-swimming larval lice, or copepodites, to salmon.
"Chemical signaling is believed to play a key role in host-parasite communication, and scientists have confirmed this," said CrispResist project co-ordinator Nicholas Robinson, in a Nofima press release.
The study involved analyzing water conditioned by Atlantic salmon, Pacific salmon, and other fish species to identify semiochemicals. Behavioural tests confirmed that water conditioned with salmon stimulated lice activity, suggesting the presence of kairomones. However, deterrent compounds were also detected, indicating that Atlantic salmon may possess some ability to repel lice.
The research further investigated the chemical composition of mucus from Atlantic salmon families with varying levels of resistance to sea lice. Mucus from salmon with higher resistance was less attractive to lice, whereas mucus from more susceptible salmon stimulated lice behaviour.
The findings highlight differences between Atlantic salmon and certain Pacific salmon species, which are more resistant to sea lice and can eliminate them during early parasitic stages, the researchers said.
The CrispResist project aims to enhance salmon resistance to sea lice by identifying the genes and mechanisms responsible for these differences. The study’s results contribute to this effort by pinpointing potential targets for future research.
Senior fish health scientist at Nofima, Aleksei Krasnov, emphasized the need for further research. "Overall, the findings suggest that host-parasite communication is highly complex and likely involves multiple cues," he said, adding that further molecular research is a "promising approach" in better understanding of semiochemicals in this context.
The CrispResist project, funded by the Norwegian Seafood Research Fund (FHF), involves 12 scientific and industry partners. Key contributors include Rothamsted Research in the UK, the University of Gothenburg in Sweden, Bigelow Laboratory for Ocean Science in the USA, and Nofima in Norway.
