When you think of Scottish salmon, you think rural and wild Scottish Highlands, which in part is true, however there is nothing wild about the Atlantic salmon industry. All Atlantic salmon you eat is farmed and it is important to know your Scottish salmon.
Salmon start their life in freshwater and migrate to the ocean as young adults.
Freshwater stages – takes place in freshwater hatcheries.
- Just like many other animals, salmon start their life as eggs. Farms in Scotland usually obtain eggs from specialised suppliers (commonly based in Norway or Ireland), which remove eggs from broodstock (a group of mature salmon used to breed and are selected based on characteristics such as growth, disease resistance, maturation rate or colour). The eggs are then laid down in trays or silo systems. After 25-30 days fertilised eggs show “eyes” and unfertilised eggs are removed by a process called “shocking”. They can take 2-6 months to hatch.
- The developing eggs then enter the second stage of their life called the alevin stage. At this point the Salmon are still very small, less than 2.5 cm to be precise! A sac containing the remainder of the yolk develops which they feed on. The yolk sac is slowly absorbed over time, following which alevins will “swim up” in the water column, showing readiness to first feed.
- Once a young salmon has absorbed its yolk sac it is called a fry. This is a rapid growth stage and the fry starts to feed.
- Salmon fry that reach a length of 6.5 cm (2.5 inches) are referred to as parr. The parr develop camouflaging vertical stripes.
- A Smolt is a stage of a salmon life cycle when the fish is getting ready to go to sea. ‘Smoltification’ is a complex developmental transformation, involving physiological, biochemical, morphological and behavioural changes which allows young parr salmon to transition from living in freshwater to living in saltwater. Light and temperature processes can be manipulated artificially to induce early smoltification in salmon farms. Smolts are distinguished by bright silvery colouring.
Saltwater stages – take place in sea pens
- When smolt are ready to go to sea, they are transported from hatcheries in specially designed boats (wellboats) or trucks (tankers) to open net sea pens. These sea pens are cage structures consisting of large nets suspended from floating walkways which are anchored to the seabed. Larger farms may have cages suspending nets reaching depths of 15-18 m. Several of these cages may be grouped together to form a seasite. Once at sea, the fish develop into adult salmon. On farms it takes 14-24 months to reach a full-size adult. In the wild the salmon return to their natal river after 24-36 months to spawn.
- Fish weighing 2kg upwards are then harvested. Harvesting takes place throughout the year, although most take place in the last quarter of the year as this is the period of best growth. After a site is harvested, good practice is to fallow the location for a period of 6 weeks or more before introducing a new generation of fish.
To learn more about Scottish aquaculture, the environmental impacts of Scottish aquaculture and what to look out for when purchasing Scottish salmon products check out our detailed website or contact us at info@fidra.org.uk.