1. Introduction
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. The life cycle of an Atlantic salmon depends on two different aquatic environments. Mature fish spend most of their lives at sea returning every twelve months in freshwater to spawn, making them anadromous.
Atlantic salmon has become a widely produced commodity, with a large volume produced from farming practices. In Norway alone, salmon production has surpassed 1 million tons. Salmon farming is the second largest industry in Norway, following the oil industry, and in Chile, it is the second largest industry after the copper industry. Other countries with a salmon farming industry include Scotland, Canada, the Faroe Islands, and Tasmania.
To reduce production costs and improve logistical control and safety, Atlantic salmon smolt (salmon fry weighing approximately 100 grams and ready for transfer into seawater) are mostly produced in land-based Recirculating Aquaculture Systems (RAS) facilities. However, the grow-out stage to market size is mostly done in cages in both Norway and Chile.
2. Key notes for when considering Atlantic Salmon
- In General:
i. Offshore sites for cage farming are limited, and good sites have already been exploited.
ii. The market has been developed more than for any other farmed species. Though, it’s still possible to tap into this large and well-established market with a premium product. This is largely made possible by the extensive experience and knowledge in producing this species; and that demand still exceeds production.
iii. The price of Atlantic salmon has only been increasing over the past decades.
iv. The supply chain of Atlantic salmon eggs is commercially well developed, and it is possible to purchase eggs to match almost any scheduled production plan.
v. The technology used in all phases of the Atlantic salmon farming process has been well-proven.
vi. Atlantic salmon are well-domesticated and genetic selection for performance has been carried out.
vii. Genetic and eco-pollution from farmed Atlantic salmon and issues related to sea lice are major concerns in cage farming. In some cases, sea lice are dealt with by introducing fish into the cages that prey on them. However, chemical treatments are still used in many places, which have considerable impact on marine life around the cages.
viii. Escapes from cages have the potential to damage or reduce the natural populations of Atlantic salmon in the rivers. Farmed fish are domesticated and their genes are selected for farming, not for survival in the wild. Therefore, when escape occurs, if interbreeding between farmed and wild fish occurs, it can negatively impact the new generation of wild stocks.
- In relation to RAS farming of Atlantic Salmon:
i. Farming of Atlantic salmon smolt in RAS is well developed. On a global scale most Atlantic salmon smolt are now produced in RAS farms.
ii. RAS farming of juveniles up to approx. 1000 grams seems to work relatively well.
iii. RAS farming of Atlantic salmon beyond 800-1000 grams can be more challenging. This is explained by the requirement of a lower density compared to the generally considered and expected optimal high densities production found in RAS farms.
iv. A six-batch per year technology for producing Atlantic salmon smolt, which can supply year-round smolt for the RAS production units, has been developed and is in full operation. This technology was originally developed by Dr. Bent Urup.
v. With advanced RAS technology Atlantic salmon can be produced without causing the environmental problems associated with cage farming. This presents an opportunity to expand Atlantic salmon production beyond the limitations set by suitable sites for cage farming.
vi. The flesh quality of Atlantic salmon depends a lot on the swimming activity of the fish. In RAS farms, when considering fish biology/behavior, it is possible to tailor design the system in a way that optimizes the water velocity/swimming activity relationship. This allows Atlantic salmon to notably increase the buildup of proteins instead of fats, which improves both the taste and the texture of the filet. In this regard, it might be possible to develop a premium market for this species.
vii. In RAS farms the fish can be produced 100 % free of parasites. In this regard, it might be possible to develop a premium fish for the sushi market.
viii. The farming of Atlantic salmon smolt in RAS systems has been extremely successful. By gaining control of diseases and perfectioning the logistics behind the production while reducing production costs, RAS is now the dominating production method for salmon smolts. BUT, the dimensioning knowledge from smolt farms cannot be transferred / applied directly into the design of growout systems. A growout system is under constant load, and when considering post-smoltification Atlantic salmon the optimal growing temperature, the feed conversion rate efficiency and the density are lower compared to pre-smoltification stages (not what one would expect). In short, this impacts the biofilter of the growout RAS facility, resulting in a biofilter up to 3 times bigger per ton of annual production. In addition, the required growing tank volume increases, not only due to the slower growth of the bigger fish, but also due to the reduced fish density. Therefore, and in general, carefully bio-modelling production before dimensioning is essential when designing a RAS facility.
ix. The ideal production temperature for Atlantic salmon in RAS is in the range of 12-13°C. This is rather low for RAS technology, as biofilters perform better at higher temperatures. For instance, the overall biofilters capacity could support a production volume 50% higher if the temperature was increased to 18-20°C.
x. In short, the biological characteristics of Atlantic salmon require a larger production facility which leads to higher initial investment compared to RAS facilities built for other potential species. For instance, compared to Steelhead salmon, the Atlantic salmon RAS facility would have an expected increased cost of approx. 50%.
3.Farming: Production stages of Atlantic Salmon
There are two main production phases for salmon: the freshwater phase (pre-smoltification) and the seawater phase (post-smoltification).
It is recommended to split the production of Atlantic salmon from eggs to smolt into five stages. Depending on targeted annual production volume and the designed logistic plan, these sections might be located in several facilities:
- Egg incubation stage (hatchery phase 1).
- Start Feeding stage (hatchery phase 2).
- Fry stage (post start-feeding stage).
- Juvenile stage (Dark phase).
- Smolt stage.
i. The first stage is the Egg incubation (Hatchery phase 1), where the eggs and fry, which still depend on their yolk sac, are kept in darkness 24 hours a day. Once the fry have hatched and absorbed the yolk sac to a certain extent (reached a size of approximately 200 mg), they are ready to start feeding on dry pellets and are transferred to a start-feeding tank.
ii. The Start-feeding stage (Hatchery phase 2) lasts approximately eight weeks, after which the fry will have reached a size of approximately 3 grams and will be ready for first grading and transfer into the next production stage: the post start-feeding stage or Fry stage. During the start-feeding phase, there will be 24 hours of light.
iii. The post start-feeding stage (Fry stage) lasts another eight weeks, during which the fry will grow to a size of approximately 15 grams and can be transferred to the dark phase. If transferred to darkness too early, the fry will not smolt properly. The minimum size of the fry before transferred to the dark phase should be 12 grams.
iv. The dark phase (Juvenile stage), where maintaining 16 hours of darkness and 8 hours of light is recommended, prepares the fry for the smolting process. The dark phase will last a minimum of 6 weeks to support a successful smoltification. Therefore, keeping the fry in dark phase for approx. 8 weeks is recommended, after which the fry should have reached a size of approx. 40 grams in weight and are ready to be transferred to the smolt stage. At this point, it is also worth considering vaccinating the group of fish.
v. Smoltification takes place 4-6 weeks after the fry are transferred from darkness into full 24-hour light. In the Smolt stage, the salinity is increased to 0.8%, and the fry are exposed to 24-hour light. After approximately 4 weeks, the fish will begin to turn silver and will be ready for transfer to the grow-out stage once they reach a size of approximately 100 grams. If the smolt are held at zero salinity until transfer, there is a chance that they will start to re-smolt back, which could cause problems once they are transferred into seawater. The increased salinity during the smolt stage further improves the immediate performance of the fish when they are transferred to grow-out, where the salinity will range from 1.5% to 3.5%.