Atlantic salmon is an anadromous fish, which in the wild spawns in rivers but migrates to sea for its main feeding and growing period. The salmon fry spends its first years in fresh water, but after reaching a weight of 20-40g it will smoltify and leave the river in early summer. After one to four years at sea, the sexually mature salmon will return to the river for spawning.
The Rainbow trout (Oncorhynchus mykiss) is originally from North America, but due to its great adaptability it has been introduced into many parts of the world. In the wild, rainbow trout can follow an andromous pattern or live its whole life in fresh water. The fast growth of the rainbow trout has made it a popular species in fish farming. In 2012 74 583 tonnes of farmed rainbow trout were produced in Norway.
Substantial drop in the use of antibiotics
Modern salmon farming is based on intensive systems. Controlling and optimising the environmental conditions increases the survival rate and considerably reduces the timeline from hatching until slaughter compared to conditions in the wild. When farmed, the salmon is protected from natural predators and has easy access to food. However, when enclosing a large number of fish in a limited area such as a tank or a net pen, the risk of disease outbreaks increases. Today, all salmon are vaccinated for a variety of diseases. The use of vaccines has resulted in a substantial drop in the use of antibiotics in salmon farming. However, good vaccines for all the virus types which can infect salmon have not yet been developed, and other measures in infection prevention are therefore important.
Salmon depend on fresh, oxygen-rich water
To maintain intensive production, substantial knowledge concerning the biology of salmon is crucial. Salmon depend on fresh, oxygen-rich water and the different life stages require different conditions of water temperature, salinity and light. To achieve fast growth and good health and welfare, it is important to have optimal environmental conditions throughout the entire life cycle.
In salmon farming, the eggs hatch in fresh water tanks on land. The fry will usually spend 8-18 months in fresh water tanks before it is ready for smoltification and transfer to net pens in the sea. The smolt usually weighs approximately 100g when it is moved to the sea, but in 12-18 months it will have reached a weight of 3-6 kg and be ready for slaughter. The salmon is fed pellets which contain a high concentration of proteins and fat. In addition to feed, the growth rate of salmon depends on water temperature, health conditions etc.