Salmon farming, disease and contamination in Scottish sea lochs

by Dr Sally Campbell

The history of this industrialised farming of the sea started as small units run by local businesses. Gradually competition and overproduction resulted in buy-outs by larger companies so that today the industry is run by multinationals. It is a similar story to chickens, egg production and other intensive food sectors, which are running into trouble meeting food and safety standards.

We all know of the spread of disease. The more crowded the environment, be they chickens, salmon or pigs, the more likely they are to exhibit a catalogue of disease, waterborne or airborne. Crowded conditions encourage both the populations of disease organisms and transmissivity of diseases. Think of Glasgow and TB in the early 20th century, chickenpox epidemics in primary schools, malaria and standing water etc. But often the control of vectors or invasive organisms by chemical spraying or by in-feed chemicals gives rise to serious knock-on events. Silent Spring by Rachel Carson showed the downside of insecticides DDT and dieldrln because they contaminated the environment, affecting birds that ate the insects, the target of the chemicals, and raptors, which ate the songbirds. But more disastrous was the long-term effect of these chemicals in the environment, soil, gravels etc affecting entire food chains. The use of tributyl tin as an antifouling agent banned 30 years ago in inshore waters and small vessels is still present and active in seabeds. The recent concern about bees and neonicotinoids, which are a relatively new class of insecticides that share a common mode of action, that affects the central nervous system of insects, resulting in paralysis and death. They include imidacloprid, acetamiprid, clothianidin, dinotefuran, nithiazine, thiacloprid and thiamethoxam. How quickly the international chemical companies have evolved these chemical warfare agents with intractable names.

So what of salmon farming and the fight against the course of nature? Increasing biomass per farm, increased use of neurotoxins to control sea lice, antibiotics, changes in the marine environment and affects on the ecosystem are all now clear and catalogued. At the same time farmed salmon in the supermarket has reduced in price progressively, artificially coloured yellow/orange by chemically produced carotenoids in the feed, containing double the fat content of wild salmon, fed by using fish oils often from Antarctica, palm oils (cheaper) and cereals (the fishmeal and fish oil from wild fish in fish feed have been partly replaced by vegetable ingredients). Wild salmon might be a super food, farmed salmon certainly is NOT despite what is said in Scottish Salmon Company’s leaflet for schools. The use of neurotoxins which are harming shell growth in shellfish is now of serious concern. To pretend that populating the salmon cages with wrasse to consume the parasitic sea lice will solve the problem is to me a fantasy. What it will do is denude the inshore reefs of Scotland of their cleaner fish, an important part of the ecosystem.

So what of antibiotics and salmon farms? On 10th October 2017, Marine Harvest said it has identified an infection that has killed thousands of salmon at one of its Lewis farms and “has taken measures to stop it spreading. The outbreak of Pasteurella skyensis, a bacteria, at a farm in Loch Eireasort appears to have affected fish already vulnerable as a result of other health challenges, such as AGD (amoebic gill disease). Pasteurella skyensis was classified as a new species in 2002 and named after a farm on Skye where it was found. “Thousands of the fish, which were around 3kg, have been lost and ‘several lorry loads are involved in this latest outbreak”. Another farm, Maclean’s Nose in Loch Sunart, where salmon have also been exposed to AGD, is believed to be infected by Pasteurella skyensis too”.
So what is Pasteurella? There are many different species of this species, and can cause a variety of disease from chicken cholera, pneumonias, symptoms in cattle, horses, cats and dogs as well as humans. It is itself not a cause of disease but frequently follows another infection, which has weakened the host.

Marine Harvest hopes that treating the fish with antibiotics will bring the infection at both sites under control. Pasteurella is sensitive to penicillins and doxycycline.
It is ironic that on the day the Chief Medical Officer of the UK, Professor Dame Sally Davies strongly condemns the overuse of antibiotics, here we have salmon being dosed with the very antibiotics that are becoming resistant to infections due to overuse, resulting in now deadly effects on human health dependent on these antibiotics.