GenusWave gives salmon a fighting chance against sea lice

October 16, 2020 | Janice Johnston | News, What's New

New seal deterrent technology reduces predation stress; boosts natural resistance to parasites

Current treatments for sea lice have been a disappointment. Better living through chemistry may not be better for salmon. The best solution may be biological.

Every fish biologist knows that salmon have an innate immunity and natural ‘mechanisms of resistance’ against parasites, including sea lice. Since the salmon’s first line of defence against sea lice is its skin and mucus production – which form a natural barrier1 – the straightforward solution is to enable each salmon to produce more mucus.

While any biological issue is multi-factorial, the calculation is to some extent valid: increase a salmon’s mucus production and sea lice will be reduced. The question is, to what extent?

Feed companies with extensive research budgets made the connection between mucus production and sea lice. Skretting, for example, has formulated specific feed additives that increase mucus production expressly to support salmons’ defence against sea lice. Their research shows a 20% reduction in sea lice.

Solution
The practical approach to produce more mucus is to remove the predation stress that interferes with their mucus production.

If salmon are experiencing predation stress, they produce cortisol and adrenaline, not mucus. As a result, predation stress makes salmon more susceptible to disease. Eliminate the predation stress and the salmon can produce more mucus.

Whilst predation stress is only one of many stressors in the life of a salmon, with new cutting-edge technology, predation stress is one stressor that can now be successfully mitigated.

Predation stress creates a serious problem
Predation stress impairs the salmon’s immune system, taxes salmon’s energy reserves and suppresses their growth rates.2 A recent study specifically linked salmon stress with “moribund fish, known as ‘drop outs’ or ‘loser fish’” that exhibit depression-like behavior and even anorexia.3 In particular, stress makes salmon more susceptible to sea lice infestations4

Predation stress without predation
Predation causes stress in fish, even where the predators cannot reach the fish.5 Anti-predation nets do not prevent this stress.

Salmon have a very strong sense of smell.6 The farther away the predators are kept, the lower the concentrations of odor in the water, and the lower the stress levels for the salmon.

Are treatments for sea lice making salmon sicker?
The current method of managing sea lice may be making the situation worse for salmon. Treatments to remove sea lice also remove the salmon’s mucus! By stripping away their mucus, the treatments make the salmon vulnerable to sea lice re-infection and more susceptible to other infections and diseases.

If a salmon is infected with sea lice, its immune system is already compromised. Stripping the salmon of its mucus rips away its only defence and is like serving the salmon up to the sea lice on a silver platter.

Keeping seals away from the salmon and eliminating predation stress may be the first step to restoring equilibrium to the salmon’s immune system and empowering the salmon to protect itself from sea lice.

The tipping point of immunity
The salmon’s immune system can manage most challenges; provided it is not overwhelmed.

“Any response…to stress requires the expenditure of energy that would otherwise be utilized for maintaining normal body functions such as growth, digestion, osmoregulation, disease resistance, healing and reproduction. Think of energy as a pie with only so many pieces; stress consumes a portion of the animal’s energy…” (Barton & Iwama, 1991. Schreck, 1982)”.

If predation stress is added to its load of other stressors, it can be a tipping point. The salmon won’t have enough energy for the optimal functioning of its immune system and won’t be able to produce enough mucus.

Keeping seals away from the salmon and eliminating predation stress should result in salmon being less susceptible to sea lice infestation.

The science
“…stress evokes elevated cortisol blood plasma levels, resulting in suppressed immune function, and drains metabolic energy, the effects of stress are cumulative (Pennell, 1991), reducing the capacity to tolerate subsequent or additional stressors. Stress suppresses the immune response and can predispose fish to disease. Stress reduces antibody production (Pickering and Pottinger 1987b, Pickering, A.D. 1987), slows the body’s response to injury or infection and increases susceptibility to pathogens.(…)

Reduced surface mucus production is associated with stress in fish, and since the mucus layer is a major defence barrier to pathogens, less mucus can mean increased susceptibility to infection. A weakened ability to engulf invading bacteria is due to the action of elevated blood cortisol that affects the fluidity of macrophage membranes, but the primary effect is that the macrophage cannot kill the pathogen after ingesting it.” (Stress in Fish, Part II, Bartelme 2004)

Bacterial disease
“Stress may also manifest itself in exposure to (bacterial) disease. Surveys in farms in Maine in 1992–1993 reported that outbreaks of Hitra, a cold water bacterial disease, started and had the greatest impact on pens already being attacked by seals, and that such pens had a 4%–5% increase in disease-related mortality.” (Nash and Iwamoto, 1999)

Greater sea lice infestation is more common in the presence of predation stress. Removing predation stress should allow for healthy surface mucus production which would reduce sea lice attachment.

More research is needed
More research needs to be done. In the meantime, salmon farmers can eliminate predation stress by keeping seals away from their pens with a new method to deter predatory seals: Targeted Acoustic Startle Technology (TAST).

Technology to empower salmon works by keeping seals away
GenusWave’s TAST is the only acoustic deterrence system for salmon farms that has been documented to be both effective and harmless in peer-reviewed and published research.

Research shows that seals do not habituate to the startle signal and TAST causes no harm to predator or prey. TAST is compliant with the most rigorous environmental standards like the ASC and the MMPA.

TAST keeps seals away from the salmon, which reduces stress on farmed salmon. Less stress means stronger immunity to disease, better appetites, faster growth, better yields and higher revenues.

The theory
Published research has established that: 1) Mucus is the salmon’s defence against sea lice infection and 2) Stress weakens the salmon’s immune system and reduces the salmon’s ability to produce mucus.

Therefore, a reduction in predation stress supports an increase in mucus production and a stronger immune system, which produces healthier, more desirable salmon and a reduced need for expensive treatments. This is a logical inference and Skretting’s research would validate the conclusion.

It’s a good theory. It makes sense. The question is, to what extent?

What are the precise benefits of eliminating predation stress
GenusWave is a science-based company and specific research is needed to link, not just in logic, but in measurable data that can quantify the extent, to which, eliminating predation stress mitigates or eliminates sea lice.

The plan for a new research study
GenusWave is designing a study to investigate the link between predator-induced stress and the susceptibility of salmon to parasite infestation. The hypothesis is that TAST could play a role in improving salmon’s immuno-response to parasites by removing predator-induced stress. This would involve deploying TAST on salmon farms and using other farms as control sites.

Calling all salmon farmers
GenusWave is seeking salmon farmers to collaborate on measuring to what extent does a reduction in predation stress correlate to a reduction in sea lice infection.

Invitation to Norwegian salmon farmers
GenusWave is inviting Norwegian Salmon farmers with sea lice issues to collaborate on an R&D license “forskningstillatelse”. The project will measure the impact of eliminating predation stress on Sea Lice attachment,Amoebic Gill Disease and Infectious Salmon Anemia.

Invitasjon til norske lakseoppdrettere med lakselusutfordringer
Samarbeid om forskningstillatelse

Inviterer alle norske lakseoppdrettere med lakselusproblemer til samarbeid med GenusWave om forskningstillatelse for å studere fordeler ved å fjerne stress forårsaket av predatorer

GenusWave ser etter norske lakseoppdrettere som ønsker å samarbeide om å måle akkurat i hvor stor grad reduksjonen av stress forårsaket av predatorer reduserer utfordringer med lakselus. GenusWave vil undersøke koblingen mellom stress forårsaket av predatorer og laksens mottakelighet for parasittangrep. Hypotesen er at TAST kan spille en rolle i en forbedring av laksens immunrespons mot parasittene ved å fjerne stress forårsaket av predatorer. En slik studie vil innebære å installere TAST på et antall oppdrettsanlegg eller på et antall merder i et anlegg. Samtidig vil andre lokaliteter eller merder uten TAST fungere som kontrollgruppe.

https://genuswave.com/contact-us/

REFERENCES
1 Jones, Simon RM, “Mechanisms of Resistance among Salmon to the Parasitic Copepod Lepeophtheirus salamonis, p. 2 (Journal of Aquaculture: Research and Development) (doi:10.4172/2155-9546.S2-003) (citing Jones SRM (2001) The occurrence and mechanisms of innate immunity against parasites in fish. (Dev Comp Immunol 25:841-852); Provan F, Jensen LB, Uleberg KE, Larssen E, Rajalahti T, Mullins J, Obach A., “Proteomic analysis of epidermal mucus from sea lice-infected Atlantic salmon, Salmo salar L.” (J Fish Dis. 2013 Mar;36(3):311-21. doi: 10.1111/jfd.12064. Epub 2013 Jan 11).
2 R.W. Rottmann, R. Francis-Floyd, and R. Durborow, “The Role of Stress in Fish Disease” (1992) Southern Regional Aquaculture Center, Publication No. 474. See also Leigh H. J. Dawson, Alan W. Pike, Dominic F. Houlihan, Alasdair H. McVicar (1999) “Changes in physiological parameters and feeding behaviour of Atlantic salmon Salmo salar infected with sea lice Lepeophtheirus salmonis” (35 Dis Aquat Org 89-99); S.D. McCormick J.M. Shrimpton J.B. Carey, M.F. O’Dea, K.E. Sloan, S. Moriyama, B.Th. Bjornsson, “Repeated acute stress reduces growth rate of Atlantic salmon parr and alters plasma levels of growth hormone, insulin-like growth factor I and cortisol.” (1998) 168 Aquaculture 221-235.
3Marco A. Vindas, Ida B. Johansen, Ole Folkedal, Erik Höglund, Marnix Gorissen, Gert Flik, Tore S. Kristiansen and Øyvind Øverli (2016) “Brain serotonergic activation in growth-stunted farmed salmon: adaption versus pathology” (The Royal Society, https://doi.org/10.1098/rsos.160030)
4B. M. MacKinnon (1998) “Host factors important in sea lice infections” ICES Journal of Marine Science, 55: 188–192.
5Jia-Jia Xu, Shi-Jian Fu, Cheng Fu (2019) “Physiological and behavioral stress responses to predators are altered by prior predator experience in juvenile qingbo (Spinibarbus sinensis)” (Biology Open 2019 8: bio041012 doi: 10.1242/bio.041012 Published 22 May 2019)
6Laura Jayne Roberts, Carlos Garcia de Leaniz (2011) “Something smells fishy: predator-naïve salmon use diet cues, not kairomones, to recognize a sympatric mammalian predator” (Animal Behaviour 82 (2011) 619e625).

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