Cause of Lewis salmon losses identified

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, said Marine Harvest business support manager Steve Bracken.

‘It’s one of these infections we’ve not seen since then,’ he said. ‘I think the fact that the fish were weakened by gill disease to begin with has meant that this bacteria could have been around before and it’s unfortunate they’ve now picked it up. What we can say is that it’s not a virus, it is a bacterial infection.’

Bracken (pictured) said it was difficult to caluclate at the moment how many salmon have been infected, but thousands of the fish, which were around 3kg, have been lost and ‘several lorry loads are involved’.

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.

However, it is hoped that treating the fish with antibiotics will bring the infection at both sites under control, said Bracken.

‘It is still a relatively young industry and we don’t have cures for all the ailments unfortunately, but in time we would hope that we would get there.

‘We believe this is a localised problem and we’ve got in place high biosecurity measures to make sure that there’s no transference between sites as a result of us, either personnel or equipment. We need to make absolutely sure that’s not going to happen.’

He confirmed that the problem at the Lewis site ‘has been grumbling on since late summer, probably about August’ – ‘it’s now good we’ve got a positive identification of what it is’. Bracken said he was unaware of any other salmon companies being hit by the infection.

The incidence across the industry of high mortalities in 2016, widely reported this week, was the combination of sea lice and AGD, but Bracken said Marine Harvest had fared better in 2017.

‘This year we got off to a very, very good start; we’ve still got AGD and lice present, albeit at a much lower level, but it’s clear that when your fish are challenged with these two things and then they are exposed to a third challenge, that takes its toll.

‘We’ve been here before and we know what can happen, but we also know what we can do to prevent the spread of it.’



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