New solutions, new challenges in fish health
Our understanding of fish health continues to advance, but fresh threats keep coming.
Wherever they were, fish farmers around the world had no shortage of health and welfare issues to contend with.
In January we reported that salmon farmers in Chile were battling against another toxic algal bloom, which starting towards the end of 2023 had cost the industry thousands of tonnes in lost fish. Farms run by AquaChile and Blumar were among the worst hit.
January also saw the first in Fish Farmer’s Aqua Agenda series of webinars. This first panel discussion focused on the topic of fish health and welfare, with contributions from: Dr Iain Berrill, Head of Technical with Salmon Scotland; Charles Allan, Head of the Scottish Fish Health Inspectorate; and Ronnie Soutar, Head of Veterinary Services, Scottish Sea Farms.
It was clear the industry has learned a lot along the way, but also that new challenges keep emerging, especially as warmer seas are encouraging the proliferation of pathogens and parasites. Also, efforts to contain one problem – sea lice – run the risk of making other problems, like gill disease, worse. You can still see the discussion online at bit.ly/AquaAgenda-health.
In February a new version of the RSPCA Assured standards for farmed Atlantic salmon welfare was announced, coming into effect from 19 May, with more than 300 new standards and amendments.
The new standards include a new set of rules covering non-medicinal treatments for problems like sea lice and gill disease, as well as 80 new standards to ensure the welfare of cleaner fish.
Delousing treatments must now be carried out only on the advice of a veterinarian, and following a risk assessment. Such treatments may only be carried out where it is in the best welfare interests of the fish.
The standards set out a range of new rules for carrying out non-medicinal treatments, such as maximum limits for fasting ahead of a treatment, maximum temperatures for thermal delousing and a rule that only one treatment can be carried out in a 28-day period, unless authorised by a veterinarian.
Meanwhile health and welfare issues continued to impact the bottom line. In March we reported that Grieg Seafood saw biological and jellyfish issues hitting its results for the final quarter of 2023. The company recorded an operating loss of NOK 67m (around £5m) compared with a profit of NOK 156m.
In April came news of support for a project looking at a potential vaccine against sea lice.
Partners from the University of Stirling’s Institute of Aquaculture, AQUATRECK Animal Health SL and Moredun Scientific have been awarded almost £50,000 from the Sustainable Aquaculture Innovation Centre (SAIC), after the initial proof-of-concept phase, which concluded last year, showed promising findings for the technique.
The latest stage of the research involves assessing the impact of the novel vaccine technology against adult lice, building on the results of the first part of the research which looked at larval stages and identified a gut protein required for protection.
If successful, the technology could be scaled up to make mass antigens available, to later be applied via salmon feeds as an oral vaccine.
In May we learned about new sightings of a parasite which turns fish flesh into a slimy jelly, which has been found in wild cod off the Norwegian coast.
So far it did not appear to have affected the country’s cod farmers but the Institute of Marine Research and the industry said they were keeping a watch on the situation.
The parasite is known as Kudoa thrysites, a type of jellyfish which attacks the cod through the skin and then gets into the muscles. After the fish dies, the parasite’s enzymes reduce the flesh to a liquified mass. The parasite is not infectious for humans.
Norwegian Institute of Marine Research scientist Arne Levsen told national broadcaster NRK: “You can literally scrape off the meat with a spoon. The entire muscle structure dissolves. So there are very strong enzymes that are in flux.”
The early part of the year continued to see reports of the infectious salmon anaemia (ISA) virus in the north Atlantic. In June we reported that a worrying number of cases of had been reported in Norway – and also in the Faroes.
In late May, Måsøval said ISA was suspected at one of its salmon farming sites in Norway.
Måsøval disclosed the unwelcome development in an Oslo Stock Exchange announcement, saying: “Strict measures have been implemented to contain the virus and prevent further spread. Måsøval will harvest the site to reduce biological risk.”
Bakkafrost also confirmed an ISA outbreak in the Faroe Islands, the first instance of the disease in that jurisdiction for a long time. Infectious salmon anaemia (ISA) was found at two Bakkafrost pens at the company’s farming site A-19 Vágur.
The news will have come as a shock for the company and to the Faroese salmon farming industry overall because the disease is particularly rare in the islands.
Also in June Charles Allan, head of the Scottish Government’s Fish Health Inspectorate gave evidence to the Scottish Parliament’s Rural Affairs and Islands (RAI) Committee.
Action to control sea lice numbers on Scottish fish farms has been successful, partly driven by the new requirement to report lice numbers on a weekly basis.
He said: “I think the sea lice situation on farms in Scotland has changed significantly… we have seen sea lice numbers come down on farms. In the last year we have offered no enforcement notices.”
Arguing that the management of sea lice in farmed fish populations in Scotland had improved, he stressed that the role of the FHI is not only to enforce penalties but to encourage continuous improvement.
In August we reported on a row between the Scottish Government and environmental groups over the timing for the introduction of tighter limits on the use of Slice (emamectin benzoate or EmBz), a key sea lice treatment.
The Scottish Environment Protection Agency (SEPA) said that stricter limits were being imposed following scientific evidence that is harmful to crustaceans. They will mean the frequency of Slice treatments will need to be reduced, and fish farmers will need to come up with alternative plans to manage sea lice levels.
The new rules are being introduced within a 48-month time frame, however, which some groups are arguing is too long for what some deem a dangerous pesticide. The industry, however, has argued that restricting the use of Slice will threaten efforts to protect salmon health and welfare.
In September, Mowi Scotland was celebrating a significant fall, year-on-year, in mortalities for the month of August, which the company said could be partly down to falling sea temperatures as part of the El Niño climate cycle.
In August 2024, Mowi Scotland recorded its lowest monthly mortality for more than eight years. The company also achieved record high feeding and growth rates in the cooler coastal waters.
Ben Hadfield, COO of Mowi’s operations in Scotland, Ireland, Faroes and Canada East, explained: “The decline of El Niño conditions, much cooler summer air temperatures and higher rainfall have all benefited our salmon farming operations. We had expected a slightly easier summer due to the declining marine heat wave evident in 2022 and 2023. This weather, combined with our enhanced mitigation measures such as the high capacity to treat salmon with freshwater and the use of bubble curtains to prevent micro jellyfish and algae entering our farming systems, have so far proved effective.”
In October, RSPCA Assured suspended three Scottish salmon farms from its animal welfare scheme after filming by activists appeared to show evidence of cruel handling practices. The farms, all on Scotland’s west coast, were operated by Mowi, Scottish Sea Farms and Bakkafrost.
November saw contrasting stories on salmon survival. The Scottish salmon industry’s woes in 2023 were highlighted in official statistics that show farmed Atlantic salmon production fell by more than 18,000 tonnes in 2023 to 150,949, a year on year decline of 11%.
The Scottish Government’s Scottish Fish Farm Production Survey 2023 also shows that the total number of smolts produced in 2023 decreased by 3.6 million (7%) to 51.5 million (see page 80 of the Yearbook for details).
More recent data, however, shows that Scotland’s salmon industry reported the best September survival rate for Scottish salmon since 2020. Figures published in October revealed a 98.18% survival rate on farms in September, which is historically the most challenging month for salmon in the sea.
The percentage of mortalities was around half the rate recorded in September last year, when warm sea temperatures in the autumn led to micro jellyfish blooms which can harm fish. After two very challenging years, survival rates in 2024 have been consistently high, reaching 99.03% in June.
2024 saw a cooler, wetter summer which has created better conditions for salmon, but industry body Salmon Scotland also stressed the importance of the resources invested in fish health over the past few years.
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