Expert topic: Atlantic salmon
by Rebecca Sherratt, Features Editor, International Aquafeed
Atlantic salmon (Salmo salar) is a species of fish synonymous with the aquaculture industry. Farmed throughout the world, the salmon industry only continues to expand year-on-year as the demand for sustainable protein grows. Salmon can be found across much of Europe, North America, Canada and Australia and are most widely farmed in Norway and Chile.
The species can be distinguished by its large mouth and silvery colour, which may contain distinct spots of green, brown or blue. Males and females can be easily distinguished, as male salmon develop a distinct kype (a hook on the lower jaw which can be displayed as a form of dominance).
Salmon farming first began in the UK in the 1800s, before being further popularised in Norway in the 1960s through sea cage farming, which was proven to increase salmon to a marketable size and ensure increased profitability. Following these developments, farmers soon began to establish salmon farming facilities in Canada, Northern America, Scotland, Australia and Chile.
The rapid increase in salmon farming has led to decreased prices, as production continues to outpace demand. Despite this, a shift is being exhibited towards a rising demand for sustainable protein, which can be readily provided by salmon. As salmon has proven challenging to sell at or above cost of production, many countries have implemented quality checks.
In 1990, 225,642 tonnes (t) of salmon were produced globally, which has seen a significant increase year-on-year. In 2015, 2,381,579t of salmon were produced, 90 percent of which is specifically Atlantic salmon. The primary market for Atlantic salmon imports is Europe, North America and Japan.
Salmon do not have any strict form of protein requirement but require many essential amino acids to ensure proper growth, such as histidine, leucine, lysine and methionine. The dietary requirements used for Atlantic salmon is notably similar to that of Rainbow trout (Oncorhynchus mykiss). Essential elements needed by Atlantic salmon are also notably similar to that of terrestrial animals, such as zinc, selenium, iron, magnesium and phosphorus.
Salmon feeds are primarily made up of fish meal and fish oil, but the growing demand for protein has led to the development of vegetal and insect proteins sources. Many technological solutions are now also on offer for salmon farmers to monitor their feeding processes, so fish can be fed without risk of overfeeding and excessive waste being produced. Salmon feed is primarily produced via extrusion technology, as they prefer slow-sinking pellets. Vacuum infusion is commonly used to allow fat to penetrate the pellet, ensuring that the feed contains high levels of lipids. Pellets will typically be between 1-11mm in diameter.
In order for salmon to obtain the bright pink colour the consumer market is accustomed to, salmon may be fed carotenoid pigments. Wild salmon feed on squid, shrimp and a variety of smaller fish.
Prior to being placed within silo systems, salmon eggs are fertilised and disinfected. Unfertilised eggs are subsequently removed. Egg incubation typically takes place at <10°C (50°F). Once hatched, alevins will mark their readiness for food by ascending to a higher water column. In nurseries, fish are stored and maintained at densities of approximately 50kg/m3.
Once the salmon have grown to an acceptable size, they are transferred to sea cages, typically at depths of around 15-18 metres (m) and up to 100m in diameter. It is crucial that the location of these cages accommodates the requirements of Atlantic salmon. Water salinity, flow and exchange rates must be considered. Atlantic salmon best thrive in salinities of 33-34‰ and temperatures of between 6-16°C. Salmon will typically grow in these cages for two years and are harvested once they reach 2kg in size.
Wild salmon are caught via traditional, commercial fishing techniques, primarily in areas such as Russia, Japan and North America. Approximately 69 percent of salmonid production takes place on farms, with 31 percent being wild stocks.