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Why mainly farmed fish is killed by the algal bloom


Large quantities of farmed salmon is being discarded in the areas affected by the algal bloom. Hi-res version

Photo: Michael Ulriksen

Wild fish can escape the deadly algal blooms, but farmed fish is held in cages. That is why the algae currently blooming in Northern Norway are lethal mainly to farmed salmon in the area.

The farmed salmon have only two choices as algae are entering the cage: To gather in the deep or flock towards the surface. The salmon which are dying now, are being suffocated by the Chryschomulina laedbaeteri.

“The salmon seem aware of the risk posed by large concentration of algae and know they have to escape. It is hard to say if this is caused by pain, irritation or discomfort. Either way, death by these algae is in no way good animal welfare,” explains animal welfare researcher Lars Helge Stien.

Salmon can learn

“We know from multiple experiments that salmon have relatively advanced cognitive abilities. They can be taught to associate something they instinctively fear, with food. Flashing lights mean feeding time, for example” says Stien.

“Salmon that have been taught this, may even display signs of aggressiveness and frustration if lights are flashing, but no food is given.

Fish will avoid pain

Fish have neural transmitters that communicate with the brain via the spinal cord, just like mammals.

“They learn to avoid painful situations quickly and may show long term changes in behavior after being treated roughly,” Lars Helge Stien says.

Fish that are given sedatives also react less to presumed painful stimuli than non-sedated fish.

Blooms will occur

Different algae are a natural part of the marine ecosystem. From time to time, harmful blooms like the ones currently taking place in Northers Norway may occur. This is caused by a host of factors: Weather, currents, nutrients, algae composition etc.

More on that subject: What we know about the so-called "killer alga" in Northern Norway