Globally, there is a huge demand for seafood. Fishing from the world's oceans has reached its limits and many fish species are endangered. As a result, the farming industry is playing an increasingly important role in meeting the demand for fish, also in the Nordic countries.
But after many years of an increasingly intensive fish farming industry, many warning lights are flashing. Not least the high mortality rate among farmed salmon. NordForsk has funded a total of nine research projects, each of which has endeavoured to find more sustainable solutions for the fish farming industry.
One of them is the project “Physiology shapes the happy salmon - a systems approach to sustainable feeds for stimulation of growth, welfare and survival (Happy Salmon)”. It is led by Elisabeth Jönsson from the University of Gothenburg.
“The salmon industry wants to farm more fish and farm them more intensively, which puts more pressure on the fish. A lot of things happen inthe salmon before the period when they move from freshwater to saltwater. This process is called smoltification, and the salmon is called smolt when it is ready to move to sea water. What we have done in the Happy Salmon project is to investigate when it is the most optimal time to move salmon to ensure the best possible animal welfare from a sustainable perspective. We can make an important contribution to the farming industry by understanding the fish and its biology and this development process, so that we can make the fish more robust. The knowledge we have developed can benefit the industry, but also consumers, as they are concerned that the farming industry considers and respects the needs of fish,” she says.
Three things can make salmon more robust
The researchers in the project make three suggestions on how to make salmon more robust when moving from freshwater to saltwater.
The industry has so far focused on markers of the fish's gill pumps and used them as a measure of when it is ready to be released into saltwater. The Happy Salmon project, however, has found two more crucial components.
“In reality, the kidney pumps and intestinal pumps are also important, but they have been overlooked. The kidneys and intestines mature later in salmon, so what we're working on now is whether it's better to move the fish to seawater a little later. It is crucial that the kidneys, intestines and gill pumps function properly when the fish are moved.”
Research from Happy Salmon concludes that it appears to be advantageous to wait to move the fish to sea water until later than today.
“We have also looked at a second thing the industry does, which is to fast the smolt for three to seven days before they are released into seawater. We've studied how fasting affects the fish and especially the intestines, and it seems that it's actually very negative. It can affect fish growth after release for up to five months, so a very short fasting period affects the fish for a long period afterwards. It affects the gut, it wrinkles, and it becomes less efficient at absorbing water. So, one should be careful with fasting before transfer. Third, we have also tested that if we give salmon an energy-rich diet before they are exposed to fasting, they do better in seawater. This could be a way to protect the fish from the negative effects of fasting.”
What happens when salmon go from freshwater to saltwater?
When farmed salmon is small, it is called a parr. It stays in freshwater until it starts the smoltification process, a preadaptation to life in sea water. In freshwater, the fish lives in water that is less salty than the fish itself, so it has to pump in ions and it sheds water because it risks getting too much water in its body. Before it enters seawater that is saltier than the fish is, it must develop mechanisms and strategies to get rid of excess salt to survive. It therefore develops pumps to pump out the salt, and it also starts to drink a little more and develops a silver-coloured skin.
Benefits for the aquaculture industry
The researchers have worked closely with the industry and had the Norwegian salmon feed manufacturer Skretting as a partner. According to Elisabeth Jönsson, one of the benefits has been gaining insight into the issues from the industry itself, building a bridge between what she calls the real world and the theoretical.
“For the farming industry, economics and production are paramount, but they also realise that if you can improve the health and welfare of the fish, the economic losses will be reduced, which will benefit the industry. If we can better understand how fish perform in different conditions and we give that knowledge to the industry, then they can work on intensification alongside sustainable nutrition.”
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