Variation in volatile organic compounds in Atlantic salmon mucus is associated with resistance to salmon lice infection

Abstract

Salmon lice are ectoparasites that threaten wild and farmed salmonids. Artificial selection of salmon for resistance to the infectious copepodid lice stage currently relies on in vivo challenge trials on thousands of salmon a year. We challenged 5750 salmon with salmon lice (Lepeophtheirus salmonis) from two distinct farmed strains of salmon in two separate trials. We found that volatile organic compounds (VOC), 1-penten-3-ol, 1-octen-3-ol and 6-methyl-5-hepten-2-one in the mucus of the salmon host after salmon lice infection, were significantly associated with lice infection numbers across a range of water temperatures (5 °C, 10 °C, 17 °C). Some VOCs (benzene, 1-octen-3-ol and 3,5,5-trimethyl-2-hexene) were significantly different between lines divergently selected for salmon lice resistance. In a combined population assessment, selected VOCs varied between families in the range of 47- 59% indicating a genetic component and were positively correlated to the salmon hosts estimated breeding values 0.59–0.74. Mucosal VOC phenotypes could supplement current breeding practices and have the potential to be a more direct and ethical proxy for salmon lice resistance provided they can be measured prior to lice infestation.

Applying genetic technologies to combat infectious diseases in aquaculture

“…These compounds are secondary lipid oxidation products which have been linked to host identification in biting insects such as mosquitoes and midges 148–150 . The concentration of these compounds in mucus differs between different families of Atlantic salmon (37%–58%) fed the same diet and is associated with higher lice counts in individuals 151 …”

“… 148 , 149 , 150 The concentration of these compounds in mucus differs between different families of Atlantic salmon (37%–58%) fed the same diet and is associated with higher lice counts in individuals. 151 …”

Reduced Infestation Levels of Lepeophtheirus salmonis in Atlantic Salmon (Salmo salar) following Immersion Exposure to Probiotic Aliivibrio spp.

“…Antimicrobial peptides released from the skin of salmon will also trigger this behaviour by activation of chemosensory neural activity [28]. Recently, specific volatile organic compounds in the fish mucus were shown to be associated with salmon lice resistance [29]. As the exact sequence of events that ends with successful attachment is still not understood, host mucus composition undoubtedly plays a part in the host selection process.…”

“…The exact nature and the multitude of compounds produced by salmon that attract copepodids and induce attachment are largely unknown [26]. However, ionotropic receptors in the salmon louse have been associated with host-seeking behaviour [27], and molecules found in salmon mucus have been associated with lice activation [28] and lice resistance [29]. The reported cost to the industry from lice treatment is high-USD 0.42 (NOK 4.25) per kilo salmon produced [30]-in addition to biological costs associated with growth reduction and biomass losses estimated to USD 0.44 (NOK 4.4) per kilo [31] in Norway based on figures from 2016.…”