New structure discovered in salmon lice
Amritha Johny at Nofima has, for the first time, described a previously unknown structure at the very front of the salmon louse’s body. Resembling a small spike, it may play a role both in how the louse senses salmon and in its initial attachment to the fish’s skin.
The structure, named the rostral spike, is visible at the stage when salmon lice need to find a host. The discovery could offer new opportunities to develop tools for controlling salmon lice.
Read the publication here: Host–Parasite Interaction: A Rostral Spike-like Structure in the Infective Stage of Salmon Lice (Lepeophtheirus salmonis) and Its Putative Role in Sensing and Initial Attachment to the Host
The rostral spike was discovered while examining copepodids under the microscope. This is the free-swimming infective stage, when salmon lice actively seek out and infect a host.
Amritha Johny, a fish health researcher at Nofima, set out to study salmon louse behaviour. This would give her a better basis for investigating how the louse affects salmon health.
Johny used wild salmon lice collected from farmed salmon, as well as laboratory strains. Egg strings hatched and developed into copepodids in Nofima’s laboratory at Ås. The lice were initially screened by microscopy at Nofima, before samples underwent further analysis using electron microscopy at the NMBU Imaging Centre.
She observed that salmon lice spend considerable time sensing, probing and penetrating the skin. This small spike-like structure appeared to be highly active during that process.
“The fact that it moved made me curious, and I wanted to find out what it was,” says Johny, explaining how she became aware of the unknown structure.
She detected the rostral spike in every louse she examined under the microscope. She also consulted leading researchers in the field, who were not familiar with the structure.
What does the rostral spike do?
Microscopy showed that the structure is flexible and moves in coordination with the rest of the body. It can also be extended from, or retracted into, the body shell. The images further revealed a pore-like opening near the point where the spike attaches to the body.
“There are many “mysteries” to solve about how salmon lice find and interact with their host. Amritha Johny has identified an appendage on the lice that has gone unnoticed in previous research, says senior researcher a Nofima, Nick Robinson. Robinson is leading a very large international research project “CrispResist” about discovering the mechanisms underlying cross-species variation in host resistance to sea lice.
“If the salmon louse’s ability to detect and infect a host depends on specialised structures such as this rostral spike, it may be possible to disrupt the process before the louse has time to attach to its host,” says Johny.
In an initial investigation, Johny did not find the structure in another louse species, Caligus elongatus. This may indicate that the rostral spike is unique to the salmon louse, Lepeophtheirus salmonis.
That could make it a more specific target for new salmon louse control measures. However, Johny stresses that further research is needed before scientists can establish exactly how the rostral spike functions. Among other questions, researchers need to investigate the structure in greater detail and determine its precise role.
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