Salmon Farming

The Atlantic Salmon (Bradán) grows to a maximum length of 150 cm and the broodstock are the parents of all the farmed fish.

Early Life Cycle

The process to take eggs from the female fish and milt from the male fish is called stripping. Stripping is exercised with smooth backward strokes along the belly of the fish. When eggs and milt are mixed the result is fertilised eggs. To allow the fertilisation to take place, water has to be added to the mixture. After a few minutes the eggs are washed to get rid of the excess milt. Then the clean eggs are placed in a purpose built hatchery. In the hatchery the eggs are laid in slowly running fresh water. 

From First Feed to the Sea Pen

The first few weeks after hatching, the alevin (young fish, fry) live on the food in the yolk-sac on their stomachs. When most of the yolk is consumed the fry are moved into large shallow fish tanks, which hold up to 10,000 fish per square metre. After the yolk has been absorbed, the alevin is weaned onto a formulated diet provided by the farmer. The first feeding period lasts for 6 weeks, and then the fish are sorted by size and put into larger tanks (a process known as grading). As the fry eats and gains weight, it develops the distinctive markings of a freshwater salmon. Weighing about a gramme, it is now termed a parr. The parr get transferred to larger freshwater tanks or freshwater cage systems, where they are subjected to natural daylight.

It takes approximately one year for the fish to be ready for the seawater stage. During this period, the fish are graded regularly so as to ensure best growth results. The temperature and light conditions are very important for the physiological development of the fry into a smolt. 

 

Introduction to the Sea

When the fish has gone through the physiological changes to become a smolt, it is then fit to tolerate the salty seawater without danger of dehydrating. The fish can now drink seawater and excrete salt through the gills.

In the spring the smolt, which is now between 80 and 100 grams, is placed in sea pens. Pens are round, square or polygon with a diameter of 30 metres and above, and with a depth of 15-20 metres. The round pens normally are built of plastic, while the square pens are made of steel. When smolts reach sexual maturity they become known as grilse. In the wild, this is the time when they get ready to spawn and return to the estuary of the river of their birth. On the farms these grilse are graded out and harvested as they stop growing and no matter how much extra food is fed to them they will not get any bigger. This is because all their energy now goes into egg or milt production and not growth.

Feeding the Fish

The feed accounts for approximately half of the operating expenses experienced by the fish farming industry. The quality of the feed and how it is used (feeding regime) is, therefore, of crucial importance. The feed and feeding regime may influence growth rate, gain per kg feed eaten (feed conversion ratio), loads of organic matter to the environment, susceptibility to diseases, etc.

Harvesting and Preparation of the Fish

Usually the fish are taken from the pen with a landing net, but some processing plants have invested in fish pumps that pump the fish from the pen directly into the plant. Before slaughtering the salmon is anaesthetized. The guts are removed following slaughter, and the fish are washed in clean fresh water. They are then stored in tanks with ice and water to wait further processing. Fish to be sold fresh and whole are packed in crates with ice. Fish requiring processing are filleted manually or by machine.