Lice on sea trout are increasing in new areas of Norway, report alerts

This year's edition of the Institute of Marine Research risk report for Norwegian fish farming has revealed that sea trout and char, currently very prevalent in areas from Rogland to Trøndelag, are increasing in other areas. Because the number of fish in the spring is increasing from Helgeland - to Vest-Finnmark, the release of lice is also increasing in the same areas.

On the other hand, scientist Ørjan Karlsen confirmed that "the risk of salmon lice having a population-reducing effect on both sea trout and char is greater than it is for salmon."

Also, the report explains that in recent years, researchers have become more and more concerned about the sea trout and partly the sea eel due to both staying in the coastal and fjord areas during the summer. This is the same time there are most lice, in contrast to the salmon smolt, which relatively quickly swims through and out to sea.

Finally, scientists remember that soft lice on wild salmon and sea trout, in particular, are "heavily attacked by the parasite". Consequently, salmon lice are still considered a "major risk".

More amount of fish, more parasites

"The breeding facility contains several 100,000 fish. Even if each facility stays within the statutory limit for how many lice they can have, they will still have many 1,000 lice that will again have offspring," Karlsen explained.

It seems that naturally, the salmon louse has evolved to endure as a species despite having limited hosts to cling to. So there is a high mortality rate for the lice larvae - most starve to death as they cannot find a fish that they can live on.

"The solution from nature's side is that each holus develops egg strings containing several 100 eggs. When these hatch, she develops new ones and can thus have several litters during a summer season," he concluded.

As the farming activity increased, the food supply for the parasite has changed intensively and more of the offspring also survive.