Lifecycle: Salmon

Lifecycle: Salmon

Around 9 million Atlantic salmon are farmed in Tasmania each year. Current scientific evidence demonstrates that fish are sentient animals, capable of experiencing pain and suffering.

Breeding
What is Aquaculture
Aquaculture may be land-based - in large tanks or ponds - or at sea in large pens. The production of Atlantic salmon is a combination of land-based and sea-based farming systems.
Fish Welfare
The available scientific evidence demonstrates that fish are sentient animals capable of experiencing pain and suffering.

Fish must therefore be treated humanely and practices that have the potential to cause pain, injury or suffering avoided. It is essential that those responsible for managing farmed fish ensure fish welfare is an integral part of every aspect of production every day.
Fish Behaviour
Expectations around normal fish behaviour in aquaculture systems includes fish being able to swim and maintain body position in the water, being able to school or shoal, and being able to avoid aggressive encounters. Fish welfare is also about fish having sufficient oxygen, having enough food, and being free of injury or disease. It is vital that anyone in charge of managing or handling fish be able to identify normal and abnormal appearance or behaviour and be able to address the cause of such abnormalities. Handling during husbandry or transport of fish should preclude any signs of stress such as excessive splashing or burrowing, gill flapping, gaping, body rolling and mortalities.
Did you know?
Farmed Atlantic salmon will spend 10 to 16 months in freshwater followed by 14 to 18 months in seawater...
Broodstock
Farming of Atlantic salmon begins on land at the breeding farm where ‘broodstock’ (sexually mature fish) are held in large freshwater ponds or tanks.

In Tasmania, salmon farmers use only female fish in the grow-out phase because the relatively warm seawater temperatures can result in rapid sexual development in male fish which, in turn, results in greater disease susceptibility and poor meat quality. A common practice in aquaculture, therefore, is sex reversal of some female broodstock resulting in ‘neo-males’. In aquaculture, by crossing neo-males with normal females, only female offspring are produced. Once a year, usually in autumn, individual broodstock are anaesthetised by submerging the fish in a water bath containing anaesthetic. While anaesthetised, eggs and ‘milt’ (sperm) are removed from female and neo-male fish, respectively. While some female fish are allowed to recover from the anaesthetic and are released back into the ponds or tanks, the method of milt removal from neo-male fish requires euthanasia.
Incubating and hatching
Eggs and milt from selected broodstock are mixed together to produce fertilised eggs.

The fertilised eggs are then placed in purpose-built incubators at specialised hatcheries where their environment aims to mimic egg incubation in the wild, for example, by providing substrate in which eggs can nestle and clean water flow providing plenty of oxygen for the eggs to grow. As the small pea-sized eggs develop, the eyes of the salmon can be seen as a black dot on the orange egg. The incubation period is measured in ‘degree days’ and is usually 450 degree days. This means that if, for example, the water temperature during incubation is 8 degrees, the incubation period is around 56 days. The hatchlings (called ‘alevins’) absorb nutrients from a yolk sac attached to their bodies and they remain in the hatching environment for another month or so at which time they are able to feed independently.
Growing
Freshwater Stage
Once the hatchlings are able to feed independently they are referred to as ‘fry’ and are transferred to small freshwater tanks within the hatchery.

Whilst in the hatchery, the fish are vaccinated against diseases that they may be exposed to later in life. As the fish grow, they are transferred to bigger tanks and, at one year old, they are referred to as ‘parr’. Distinct vertical markings appear on the fish which, in the wild, serve as camouflage. After about a year growing out in large tanks at the hatchery, the fish undergo further transformation: the vertical markings are replaced by a silvery sheen and the edges of the fins darken. At the same time, a physiological change occurs internally which allows the Atlantic salmon to survive in seawater. This process is called ‘smoltification’ and the fish, at this stage, are referred to as ‘smolts’ and they are able to be transferred to sea.
Water Quality
The enclosure nets are kept clean to prevent build-up (‘biofouling’) of algae and micro-organisms that impede the flow of water which supplies oxygen and removes waste products and other organic matter from the sea pens. A reduction in oxygen supply causes stress levels (and susceptibility to disease) to rise. Copper and zinc-based antifoulants are no longer used on nets thus eliminating the potential for these metals to contaminate the environment. Instead, nets are regularly cleaned in situ to prevent biofoul build-up on the nets affecting oxygen supply to the fish.
Feed
Because Atlantic salmon are carnivorous, their diet contains mainly animal proteins, but also some vegetable ingredients, vitamins and minerals.

Fish meal and fish oil are also included in the diet providing proteins, lipids and essential fatty acids. For salmon, fish oil is the only source of omega-3 fatty acids. Fish meal and fish oil is obtained from wild-caught species of small ocean fish (e.g. anchovies, sardines) and from processing waste (trimmings) from fish caught for human consumption. In the wild, Atlantic salmon eat an estimated 10kg of forage fish for every 1kg of body weight. Efforts to reduce reliance on wild-caught fish in the salmon industry have seen a significant reduction in fish oil/meal as a feed ingredient. At present, farmed Atlantic salmon require around 1.7kg of wild-caught fish to produce 1kg of salmon. Research continues in this area with the aim of reducing/removing wild catch and further lowering fish oil/meal content in the feed without compromising fish health. Aquaculture companies can purchase their feed from suppliers who source marine ingredients from responsible fisheries. Antibiotic use is restricted to tanks or pens where the fish require treatment for a bacterial infection. Vaccination and improved diets are seeing an on-going reduction in the use of antibiotics in Atlantic salmon farming.
Colour
The orange-pink flesh colour of Atlantic salmon is a result of a carotenoid pigment called ‘astaxanthin’ which salmon in the wild would digest when eating plants, microbes, crustaceans and other foods it would naturally eat.

In farmed Atlantic salmon, synthetic carotenoids are added to feed to provide fish with the same anti-oxidant properties (preventing cell damage) and resulting health benefits such as disease resistance that carotenoids would provide in the wild.
Marine Stage
When farmed Atlantic salmon are able to be transferred to sea, they are pumped out of their hatchery tanks through water-filled pipes and transported in large water-filled tanks to the sea shore.

From here, they may be transferred via pipes directly into their marine pens or to water-filled tanks in purpose-built boats (called ‘wellboats’) that then take the fish to their marine pens where they will grow out for about the next year and a half or so. The marine pens are large, netted enclosures which not only prevent the fish escaping but also protect them from predators such as seals. Fish grow out to an average weight of around 5kg by which time they are ready to be harvested (about the equivalent of three fish per cubic meter of water).
Environment
Good water quality and water flow is not only important for the health and survival of the farmed Atlantic salmon but also for the ecology and biodiversity of the farm’s surrounding environment.

Both the fresh water and sea water stages of Atlantic salmon farming are subject to government regulation and licensing conditions that incorporate production aspects such as the location of the farming lease, the size of the lease, potentially polluting activities and waste management. As part of their license conditions, farms are required to ensure that there is no significant visual impact 35 metres beyond the edge of the lease. Remedial action is required if license conditions are breached. Salmon farms are subject to ongoing monitoring of the water and sea bed underneath and around the sea pens. Any environmental impact of farms can be reduced by preventing feed wastage, by promptly removing dead or moribund fish from the sea pens and by fallowing sea pens regularly.
Processing
Harvesting and Slaughter
At harvest, farmed Atlantic salmon may be removed from their sea pens through large pipes and transferred to special harvesting boats that sit alongside the pen.

Alternatively, the whole pen is slowly towed towards shore where fish are transferred directly to a slaughter plant. Before slaughter, fish may be fasted for a few days in order to reduce the oxygen demand required to digest their food. By reducing this oxygen demand the fish are better able to cope with the harvest process. The harvest and slaughter process keeps fish in water as long as possible before they are stunned using a percussive blow to the head. Subsequently the unconscious fish are bled and immersed in an ice slurry for transport to processing plants where they are gutted, washed and processed into fresh, frozen or smoked product.
Farming RSPCA Approved Atlantic Salmon
The Standards require that all persons managing fish are trained and competent in their required tasks; that handling of fish is carried out in a manner that is low stress; and, that all husbandry and management practices limit any negative impacts on the fish. The Standards aim to ensure that fish be held in water of good quality and farming practices aim to provide all fish with sufficient oxygen and feed; freedom from injury, stress, deformation or disease; the ability to exhibit normal swimming and schooling behaviour and to escape aggressive encounters. The RSPCA Standards also require that a farmed Atlantic salmon producer be compliant with a recognised aquaculture certification scheme that promotes best environmental practice.