The Atlantic salmon is a fish that can be mainly found in the northern Atlantic ocean, as well as the rivers tributary to the north Atlantic and north Pacific ocean. Scientifically, it is known as Salmo salar and it is a member of the family, Salmonidae. The adult fish is known to be an excellent jumper. In fact, the word, 'salar' means leaper. This fish is not closely related to the six species of Pacific salmon. It is a distant relative of the Pacific salmon, but closely related to the brown trout, which is also known as Salmo trutta.
More Information about Atlantic Salmon
Commercially, they are known as the black salmon, silver salmon, slink, bay salmon, spring salmon, kelt, grilt, and landlocked salmon. They can be farmed quite easily. In fact, they are widely grown in the United States, Canada, Norway, and Chile.
It can grow up to a length of about 70 to 100 cm. An adult fish can weigh somewhere between 2 to 10 kg, though some can weigh almost 30 pounds, i.e., 13.6 kg. The young fish looks quite different from the adult due to the presence of blue and red spots on its body. As it matures, the body color becomes silvery blue. The most distinguishing feature of the adult fish is the presence of black spots above the lateral line. However, its caudal fin is not spotted, and except for its adipose fin, all other fins have black border. The fish also possesses well-developed teeth.
Habitat and Distribution
Atlantic salmon can be found in both freshwater rivers and oceans. They begin their life in freshwater and remain there for the first 2 to 3 years of their life. So, the young fish live in the river where they are born, and then migrate to the ocean when they mature and undergo some physiological changes.
They remain in the ocean for 2 to 3 years, after which they return to their natal river in order to spawn. They can be largely found in Canada, Finland, Germany, France, Great Britain, Iceland, Ireland, Lithuania, Latvia, Russia, Poland, Sweden, United States, Spain, Denmark, and Norway. The coastal rivers of Iceland, North America, Europe, and northwestern Russia are the major sites of reproduction for them.
The young fish starts hunting and feeding once its yolk sac is absorbed by the body. It primarily feeds on tiny invertebrates. As it matures, it starts hunting and feeding on small fish and salmon eggs. It also eats black flies, mayflies, caddisflies, and stoneflies. The adult fish mainly feeds on amphipods, capelin, crustaceans, Arctic shrimp, Arctic squid, sand eels, and herrings.
As has been mentioned already, the coastal rivers of Iceland, Europe, North America, and the northwestern Russia are the breeding grounds for the Atlantic salmon. The areas with coarse and loose gravel or rubble are the suitable spawning sites for these fish. The spawning site should have moderately strong current so that the eggs do not get smothered by silt.
Usually, an adult female fish builds a nest by digging the gravel bed of a stream with the help of its tail, and then lays eggs there. After laying the eggs in that depression, it covers them by shifting gravels with the tail. A female fish can lay about 1500 to 1800 eggs per kilogram of its body weight. The ideal time for spawning is mid-October to November, and the eggs usually hatch in March or April.
This fish exhibits the anadromous migration pattern. The salmon eggs hatch in the month of March or April, and the young fish begin their life in freshwater. A newly hatched young fish is called alevin. So, 'alevin' is the first stage of its life cycle, where the fish remains in its breeding ground. In this stage, it derives nutrients from the yolk sac. Gradually, the young gills develop. When the yolk sac is completely absorbed by the body, the young salmon starts hunting, and leaves the breeding ground in search of food. This stage is called the 'fry stage'.
The final freshwater stage is known as 'parr'. The 'parr' develops into 'smolt' by undergoing some physiological changes, which enable it to tolerate salt water. As it attains the 'smolt' stage, the fish starts its journey to the ocean. During this stage, it grows quite rapidly. It spends about 2 to 4 years in the ocean, and then finally reaches the 'grilse' phase. Now, it is ready to return to its natal river, and during the journey, it again undergoes some physiological changes.
The sense of smell is believed to help this fish return to its natal river. During this stage, the digestive system of the fish ceases to operate, and hence it can live without eating for up to 12 months before spawning. It does not die after spawning, and so it can repeat the entire migration cycle again. The Atlantic salmon can live for about 15 years on an average.
Salmon are not only a good source of protein, but contain very high levels of omega-3 essential fatty acids as well. They can also provide a significant amount of several crucial vitamins and minerals, like vitamin A, vitamin B1 or thiamine, riboflavin, niacin, vitamin B6, folate, vitamin B12, vitamin D, calcium, magnesium, potassium, sodium, zinc, copper, manganese, selenium, and phosphorus.
Farmed Atlantic Salmon
These fish are very sensitive to the changes in their environment. Therefore, they are first reared in shore-based freshwater hatcheries till they attain the smolt size. Later, they are placed in the floating sea cages, where they are kept for about 18 months before marketing.
The excreta escaped from these farms can pollute the surrounding water, which can prove disastrous for shellfish beds. Therefore, the farmers are required to strictly monitor the condition of the surrounding water and the ecosystem. Salmon farmers are also required to reduce the amount of excreta released into the ocean.
Salmon can also contract bacterial, as well as fungal and viral diseases, for which farmers have to use antibiotics, vaccines, and other medicines. A large part of such medications can escape into the sea water. Many people have also expressed their concern that diseases can spread from the farmed salmon to the surrounding ecosystem, which may pose a threat to wild salmon.
Sometimes, farmed sea cages fail to contain the fish, and as a result, some of them can escape into the surrounding water and reach the nearby rivers, where they can breed with wild salmon. However, efforts have been taken to reduce the accidental release of salmon with the help of efficient containment systems.
Though the 'anadromous' migration pattern is one of the most distinguishing characteristics of these fish, many species of them have found to live entirely in freshwater. These are the landlocked salmon that are commonly known as ouananiche. Owning to large-scale dam construction, as well as the degradation of water quality and overfishing, the population of wild Atlantic salmon has reduced to a great extent over the years. However, several conservative efforts have been taken by various authorities to preserve their population.