Summary Every sixth Norwegian farmed salmon dies before slaughter, partly because rapid growth as smolts (“baby fish”) leads to poor heart function. Studies show that smolts that are manipulated to grow faster than in nature become less robust and tolerate disease and de-lice less well. A study shows that smolts that grow slowly are hardier, have a better survival rate and meat quality, and require less feed. Another shows that rapid growth can lead to deformed and weak hearts, which increases mortality among farmed salmon. Slow-growing smolt can become slaughter-ready salmon before the fast-growing smolt, despite the fact that they are smaller when released into seawater. The summary is made by an AI service from OpenAi. The content is quality assured by news’s journalists before publication. In fish farming, much of the salmon smolt – i.e. the “baby salmon” – is manipulated to grow much faster than in nature. – It is no coincidence that nature takes a long time. Slow-growing smolts are hardier and will cope better, says Øystein Klakegg. He is an associate professor in aquaculture and veterinary medicine at Molde University of Applied Sciences, department Kristiansund. – Salmon smolts that are left in fresh water for a longer time survive better as adult fish than smolts that are under more pressure to grow quickly, shows Øystein Klakegg’s research. He and his colleagues have now studied 5 million salmon smolts that were 1.5 years or older when they were released into the sea in Western Norway. The researchers measured survival rates, feed requirements and meat quality. – So-called old smolt are doing better than the average in Norway, and better than younger smolt that were released in the same locations. The fact that the farmed salmon are pressured to grow rapidly early in life can be an important reason for high mortality in the pens. Mortality increases for smolt The smolt for wild salmon stays in Norwegian rivers for 2-6 years before it migrates to the sea, and by then it is usually only 15-60 grams. In many fish hatcheries, the smolt is kept in fresh water with a high temperature, and with continuous light, in order to grow faster. The smolt is often moved to seawater after six months, and can then already be 100-200 grams. 16.7 percent of Norwegian farmed salmon in sea farms die before slaughter. It is worst in Western Norway, where around 25 per cent die. In 2021, 54 million farmed fish died in Norwegian cages and 35 million hatchery fish, and all used reindeer fish (40 million) were taken out of the cages or died. In 2023, the figure had increased to over 65 million fish that died by themselves in seas and 40 million spawning fish, plus all reindeer fish (34 million). Source: The Veterinary Institute and Øystein Klakegg. Deformed and weak hearts Another study, from the Veterinary College, has shown that rapid smolt growth is linked to deformed hearts and heart disease. – Farmed fish generally have very different heart shapes. One of the reasons for this may be the rapid, intensive production of smolt in freshwater, says associate professor Ida Beitnes Johansen. – There is no doubt that this also contributes to mortality. So I think there is a huge animal welfare problem. – Are the fish becoming less resistant? – Absolutely. They become less robust. Ida Beitnes Johansen at the Veterinary College calls fast-growing farmed smolts that develop weak hearts a major animal welfare problem. Photo: Nuno Duarte / news The study shows that fast-growing smolts develop heart failure more easily. – They get worse heart function. In our one experiment, the smolt showed early symptoms of heart failure after they came out to sea. And fish that have died after deworming have more abnormal hearts than those that survive, says Johansen. One goal of getting the smolt to gain weight quickly is that the bigger the fish, the shorter time it needs to be in the sea where it is exposed to salmon lice. – The question is how wise it is, if it goes beyond organ development, says Johansen. The study at the Veterinary College shows that fast-growing smolts develop heart failure more easily. The picture shows the heart shape of wild salmon and farmed salmon. Graphics: Ida Beitnes Johansen / NMBU Veterinary College Steadily faster smolt growth When Norwegian fish farming boomed in the 1970s, it was common for the smolt to spend two years in fresh water before being released into seawater. Since then, growth has been pushed forward more and more, with the use of increased water temperature and artificial light. – The fact that farmed fish in many places never get to experience darkness is special, says Ida Beisnes Johansen at the Veterinary College. – Since the 2018 generation, more than half of the smolt that have been seen in seawater have been zero-year-olds. That means fast-growing smolt that was moved to seawater the same year he was hatched, says Øystein Klakegg at the University of Molde/Kristiansund. Klakegg emphasizes that rapid smolt growth is contrary to how wild salmon grow large and strong in their natural state. – The fish has developed over hundreds of thousands of years in nature. If you take the fish out of the natural conditions, you change much more on the fish than you might have previously thought. Wild salmon on their way up the stream in Vestre Jakobselv in Finnmark. Photo: KNUT-SVERRE HORN / news Investing in late-growing smolt Sørsmolt AS specializes in slow-growing smolt. Veterinarian for the company, Jan Gjerde, says it reduces problems with both fish diseases, salmon lice and high mortality. – The aquaculture industry struggles with enormous problems in the seawater phase: poor growth, high mortality. The important thing is that when the smolt goes into the sea, it must have quality for robustness and growth. Not necessarily very big. – If you manage to make a robust fish with good growth, he is also quite resistant to lice. Gjerde believes that many large farming companies are too busy getting large smolt. Slow-growing smolts produce salmon that are more robust against disease and lice, research shows. Photo: Vossolauget Norsk Seafood: – Responsible animal husbandry and optimal use of resources When asked about arguments for and against fast-growing salmon smolt, Jon Arne Grøttum, director of aquaculture at the industry organization Norsk Seafood, answers: – The aquaculture industry always seeks the best possible knowledge for responsible animal husbandry and optimal resource use. The industry’s own research fund works with such issues, among other things. He states that 40 per cent of the smolt that are released into seawater are so-called spring smolt. This roughly corresponds to zero-year-olds. Autumn smolt, roughly equivalent to 1-year-olds, make up 60 per cent. Answer from Sjømat Norge about fast-growing smolt 1) Approximately how much of the salmon production is based on 0-year-old, 1-year-old and possibly 2-year-old smolt? 2) What speaks for and against fast-growing smolt? 3) What is your response to criticism /claims from those who argue for more slow-growing smolt? 4) How is this question assessed by Sjømat Norge? And is there increasing debate/awareness about this topic in the industry? Answer from managing director Jon Arne Grøttum: 1) It is no longer so common to distinguish between 0-, 1- and 2-year-old smolt. This is because roe can now be hatched all year round and that in many cases the fish are kept on land in the first period. If we define spring smolt as released in the first six months, then it makes up about 40% of the release (somewhat similar to what was previously called 0-year-old). Autumn smolt (somewhat equivalent to 1-year-old) then makes up 60%. Very little of what was called 2-year-old is produced today. 2) First and foremost, it must be ensured that the operation is carried out within the framework of sound animal husbandry. For bicycling animals, growth can often be increased by increasing the temperature, but at the same time a temperature that is too high could have negative biological consequences. The industry learned that too high a temperature for fertilized roe led to malformations, which was ethically unjustifiable and unprofitable in terms of production. When we gained this knowledge, the temperature during roe production was reduced.3) Given by point 24) The aquaculture industry always seeks the best possible knowledge, both for the fish and to optimize the use of resources. At the initiative of the industry, a separate research fund has been established which, among other things, works on this type of problem. Seafood Norway’s goal is that aquaculture should always be based on good and thorough professional assessments. Abnormal heart shape occurs early in fast-growing smolts. The figure shows the difference in heart shape in wild salmon and farmed salmon at different age stages. Photo: Veterinærhøgskulen – Pushing the smolt too much Klakegg believes the farming industry is becoming more aware that high water temperature and rapid smolt growth have disadvantages. – It is probably an emerging debate that is getting stronger and stronger. It is about the fact that one might be pushing the smolt too much. If the health or environmental conditions are a little problematic in a breeding facility, we think it is an advantage that the fish are a little more like their natural state when they come out of the cages. Published 17.07.2024, at 11.49
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Fast-growing smolt contributes to high mortality in salmon farming, according to research – news Vestland
