Biological Risk: Lice, Mortality, Regulation

Lice and Fish Deaths Hit Cost, Volume and Capacity

A salmon farmer’s biology moves its earnings as surely as the salmon price. Sea lice, small parasites that feed on the fish, force treatments that cost money and stress the fish. Disease and poor water kill fish outright. In Norway, lice also decide whether a whole production area may grow or must shrink. In FY2025 fish lost in specific incidents cost Mowi EUR 49.2m in Norway alone, and Lerøy treated a third more cages for lice than in 2024.

Statutory Sea Lice Limits

Norway’s lice regulation (lakselusforskriften) sets a weekly limit on adult female lice per fish:

The tighter spring limit protects young wild salmon as they swim out to sea past the farms. A farm over the limit must treat its fish, and repeated pressure across an area feeds the traffic-light grade that sets its capacity.

Staying under the limit does not mean low cost, because farms treat their fish to stay under it. In 2024 Lerøy’s three Norwegian regions averaged 0.08-0.22 adult female lice per fish, well under 0.5, yet it treated 1,463 cages that year and 1,956 in 2025.

Traffic-Light Capacity Effects

Every two years the state grades each of Norway’s 13 production areas (PO1 to PO13) by how many wild salmon its farms’ lice are estimated to kill. It then adjusts the maximum allowed biomass (MAB), the cap on live fish in the sea, of every licence in the area:

The 2024 decision set 6 green, 5 yellow, 2 red production areas (PO3 Karmøy-Sotra and PO4 Nordhordland-Stadt red), for roughly +21,000 t of growth against -11,400 t of reduction. The decision of 19 June 2026 set 3 green, 9 yellow, 1 red: PO1, PO12 and PO13 green, PO3 red again and PO4 moved to yellow, for about 8,300 t of growth offered against about 5,300 t withdrawn (Ministry of Trade, Industry and Fisheries).

Grieg’s Rogaland farms sit in PO2, yellow in both decisions: no cut, no growth. With 98% of its 17,800 t MAB in use at year-end 2025, it had little room to add volume without buying capacity or qualifying for the low-lice exception (below).

Mortality and Survival Markers

Farmers disclose survival and the cost of incidents on different bases:

Incident-based mortality is the cost of fish lost in a specific event, a disease outbreak or a spell of bad water, beyond the normal losses through a growing cycle. Mowi put its Norwegian losses down mainly to gill issues and the knock-on effects of lice treatments. In Canada, most of its EUR 35.2m came from low oxygen in Canada East after a very warm summer, and Canada made an operational loss of EUR 1.09/kg. Lerøy blamed its lower survival on lice treatments and viral diseases.

Bakkafrost’s Scottish farming recognised DKK 172m of incident-based mortality in 2025, DKK 55m of it in Q4, mainly at its Portree site after an outbreak of Pasteurella, a bacterial disease. Scotland’s operational EBIT was DKK -17.77/kg, while its Faroese farming earned DKK 5.17/kg.

Treatments, Costs and EBIT/kg

Every treatment is a cost and a welfare event. Handling stresses the fish, which raises mortality and slows growth before harvest. So a farmer can keep lice counts under the limit and still pay for it: Lerøy’s cages treated rose 34% in 2025.

The arithmetic is the same for every farmer: a treatment or mortality cost of NOK 3/kg takes NOK 3/kg off EBIT per kg, which is a larger share of a thin margin than of a wide one.

A 12-month rolling survival rate and a monthly one measure different things, so they cannot rank farmers. Within one farmer on one basis, a fall in survival is margin lost at whatever price the fish would have fetched.

Proposed Reform: Lice Quotas

The government’s 2025 white paper on aquaculture (Meld. St. 24 (2024-2025)) proposed replacing the traffic lights with quotas for lice emissions set per production area. Parliament did not adopt quotas outright. It asked the government to study how quotas could be allocated, and to replace the traffic-light exception rule, which lets farms with low lice levels grow outside green areas, with a scheme for low-emission technology. Until new rules are adopted, the traffic lights and statutory limits apply, as the June 2026 decision shows, so model those.

Capacity Link

Biology and regulation meet at MAB. KFO, the western Norwegian farmer 55.2% owned by Austevoll, had 4,700 t of MAB against an original 5,460 t at the end of 2025: a temporary cut of 14%, more than one 6% red grade in areas 3 and 4 (Austevoll Q4 2025). The licence and MAB guide sets out each farmer’s MAB and how Norway adds capacity.