1. Introduction
Salmon has become a commodity, it is now a fish specie produced in large quantities. In Norway alone the production has now passed a volume of 1 million ton. In Norway salmon farming is the second biggest industry next to the oil industry and in Chile the second biggest next to the cobber industry. Scotland, Canada and the Faroe Islands are other countries, which have a Salmon farming industry, further there is some production in Tasmania as well.
Salmon smolt (salmon fry of approx 100 gram ready for transfer into seawater) are now mostly produced in land based RAS facility due to reduced production costs, the logistical control and safety in production. The grow out stage to market size is though in both Norway and Chile exclusively done in cages.
2. Culture Systems
- Advantages of RAS for the culture of Atlantic Salmon VS other systems
A key Issue with the existing production of Salmon in cages is the environmental issues. The BOD load (organic material) on the ecosystems are more than 100 times higher from cage systems compared to the load from a RAS facility like a RAS2020 production module, per ton production.
Two other issues with cage farming being discussed are the genetic- and eco - pollution by the farmed stocks, and the issues with sea lice. In some places the sealice problems are dealt with by adding fish into the cages which will predate on the sealice, but still in many places chemical treatments are applied, which will cause considerable impact on the marine life around the cages.
Escapes from cages on a bad timing will potentially destroy or diminish the natural populations of salmon in the rivers. The escapes will take up the space at the cost of the wild stock, but without the ability to regenerate the stocks in the rivers, as the farmed salmon are domesticated, and with genes selected for farming, not for survival in the wild.
With advanced RAS technology like RAS2020, Salmon can be produced without causing the environmental problems of cage farming, this generates an opening for expanded production of salmon as well as of other fish species, where cage farming has been very restricted by the Authorities, due to the environmental impact.
Salmon is maybe not the most expensive fish to produce in a RAS system, but the advantage of producing the salmon, is that we can enter a known market which is very big, with a premium product, and it is a specie we have a lot of experience with in production:
i. Well, proven technology in all phases
ii. Fish well domesticated and genetic selection on performance has taken place.
iii. Eggs can be purchased on a weekly basis from Island.
iv. 6 batch technology for salmon smolt, which can supply all year smolt for the RAS2020 units have been developed and in full operation. (Originally developed by Dr. Bent Urup).
v. Salmon farmed and tested in RAS systems.
vi. Some potential issues with early maturation also in RAS systems (expected 12%), but not financially critical and will be reduced further.
vii. Production from eggs to smolt (120 gram takes long time approx. 10 month)
viii. Production from smolt to harvest size 4,5 kg, in less than 12 month in RAS.
ix. RAS production costs and investments with RAS2020, equal to cage farming, but harvest logistics better (daily).
- Production stages of Atlantic Salmon
i. There are two main production phases for Salmon. The freshwater phase, and the Seawater phase.
ii. The production of salmon from eggs into salmon smolt will take place in 5 stages.
iii. The initial stage will be the hatchery. In the hatchery there will be darkness 24 hours/day. Once the fry have hatched and the yolk sac partly absorbed and the fry at a size of approx 200 mg are ready to start feeding on dry pellets, then the fry are transferred to a start feeding tank.
iv. The start-feeding phase will take approx 8 weeks, after 8 weeks on dry pellets, the fry will have reached a size of approx. 3 gram, and be ready for the first grading and transfer into the next production stage, the post start-feeding stage. During the start-feeding phase there will be 24 hours light.
v. The post start feeding stage will take another 8 weeks, after then the fry will have reached a size of approx. 15 gram, and the fry can be transferred to the dark phase. If the fry are transferred into darkness to early, they will not be smolting well.
vi. The dark phase - 16 hours darknes/8 hours light, - will prepare the fry for initiating the smolitification, which will take place 4-6 weeks after the fry are transferred from darkness into full 24 hour/day light. The dark phase will last minimum 6 weeks, and the fry will be above 40 gram when transferred to smolt stage.
vii. In the Smolt stage the salinity will be increased to 0,8% and the fry will be exposed to 24 hour/day light. After approx 4 weeks the fish will then start going silver and be ready fro transfer into smolt. The fish will then be transferred to grow out when they have reached a size of approx 100 gram. If the smolt where held at zero salinity until transfer there would be a chance that the fish would start resmolting back, which would cause problems once the fish are transferred into seawater. The increased salinity will further improve immediate performance of the fish when they are transferred to grow out where the salinity will be form 1,5% to 3,5% salinity.
3. Biology
- Family
Atlantic Salmon, also known by its scientific name Salmo salar, is one of the sixty-six species found in the family Salmonidae. As its name suggest, it is found in the Atlantic Ocean, more precisely, from the latitude of northern Spain to Iceland.
- Life cycle of the species
The life cycle of an Atlantic salmon depends on two different aquatic environments, mature fish spend most of their lives at sea to return every twelve months in freshwater to spawn, making them anadromous.
i. Fertilization
Fertilization is a meticulous process, with for first step the creation of a series of nests called ‘redds’ by the female. Using body movement allow her to dig a depression in the silt-free gravel which varies between 2.5 and 15 cm in diameter and can receive a stream velocity of around 0.5 m/s. When the redd is ready to host the eggs, the female will lay her eggs (1500 eggs/kg body weigh) that are fertilized by the release of milt from the male salmon into the water column. Finally, to protect the ova, the female will bury them to a depth than can reach 40cm.
ii. Hatching
Hatching occur around 480-520 degree-days after fertilization and alevin will remain in the redd using their yolk reserve as resources. The main energy spent by the alevin is focused on the maximization of growth and a few is spent to maintain their position in the redd (negative phototaxis).
iii. Fry stage
In spring, at around 800 degree-days, the fry begins to expose themselves to the environment leaving the protection of the redd. They are carnivorous and territorial and must find food as their yolk resource are almost gone.
iv. Parr stage
Through the growth of the fry into a parr, lateral marking start to appear making it easier to identify and acting as camouflage for the par stage. The duration of this stage varies between 1 to 8 years before undergoing significant changes, the duration is explained by the location and the temperature (higher the latitude, longer the par stage will last).
v. Smolt stage
The par-smolt transformation, also known as smoltification, is the metamorphose from par stage to smolt stage through a series of physiological changes prior to (few months) the next seaward migration. This metamorphose include a change in body shape (loosing lateral mark, change of color), an increase in skin reflectance and (Na+/K+)-ATPase in the gills. As explained above, those changes occur at different time for each individual but usually at a weight up to 60g and at an age of 1-3 years. The smolt will then start its migration with the ability to face saltwater, and once at sea, will be in search for rich feeding ground.
vi. Grilse
Then, the fish is differentiated into two names grilse and salmon. The former gets this name after coming back to their natal river stream after 18 months at a weight between 1-7kg. The latter can spend up to five winters at sea and reach a weight of 4-30kg.
vii. Kelt
Survival rate after spawning is mainly low. Usually, a mature female will spawn around 2-3 times and after the first spawning she is known as a ‘kelt’. On the contrary, mature male will not live to spawn more than once.