Atlantic Salmon Farming: A Production Guide

How Atlantic salmon (Salmo salar) is farmed: the two-phase freshwater-to-seawater cycle, smolt production, sea-cage grow-out, feed and FCR, sea lice and other diseases, and environmental issues.

Overview

Atlantic salmon (Salmo salar) is the backbone of marine finfish aquaculture and the most widely farmed salmonid, valued for fast growth in sea cages and a high market price. Production is concentrated in cold northern waters: Norway and Chile are the largest producers, together accounting for the majority of farmed salmonid output, followed by Scotland and Canada. Marine cage culture of salmon began in Norway in the late 1960s and has since grown into a multi-million-tonne global industry.

A two-phase life cycle

Atlantic salmon is anadromous, so farming follows its natural move from fresh water to the sea. Eggs are hatched and fish are reared in freshwater tanks, increasingly in recirculating systems, for roughly 12 to 20 months until they become smolts. Smoltification is the physiological change that prepares the fish for seawater; smolts are then transferred to marine net pens, where they are grown for up to about two years to harvest size.

Sea-cage grow-out

Seawater grow-out takes place in floating net pens anchored in sheltered, cold coastal sites. Cages are typically 10 to 32 m across and about 10 m deep, with volumes of roughly 1,000 to 10,000 cubic metres, and stocking density for Atlantic salmon is often in the range of about 8 to 18 kg per cubic metre. Optimal growth occurs in cool water, with growth reported to be fast around 14 °C.

Feeding and FCR

Salmon are fed high-energy formulated diets rich in protein and lipid, including long-chain omega-3 fatty acids that the fish require during the seawater phase. Farmed salmon convert feed efficiently, with a feed conversion ratio commonly around 1.2. Feeds historically relied on fishmeal and fish oil, and the wild fish needed per kilogram of salmon has been reduced over time, with plant proteins now supplying a large share of the diet.

Sea lice and diseases

The most prominent challenge is the parasitic sea louse (Lepeophtheirus salmonis), which can spread between farmed and wild fish and is managed by treatments, cleaner fish and area coordination. Major infectious diseases include infectious salmon anaemia (ISA), first identified in Norway in 1984, infectious pancreatic necrosis (IPN), pancreas disease caused by salmonid alphavirus, and amoebic gill disease. Vaccination, biosecurity and fallowing are central to disease control.

Environmental management

Concentrated salmon farms can affect the seabed beneath cages through settling organic waste and can release nutrients to the water column. Operators use good site selection, fallowing of sites between cycles, area or zone management to coordinate stocking and lice control, and integrated multi-trophic aquaculture to reduce these impacts. Effluent and benthic effects are monitored under environmental regulations.