Sunday, August 2, 2009

Salmon Fish Study

The Salmon is a large grey sea fish with black spots shaped like crosses or stars. Its adipose fin is a plain grey. It migrates in the summer and autumn months high upstream against the current to spawn. During migration the males become darker and their sides are decorated with red and orange spots, whilst the belly becomes pink. The females do not change their appearance when they migrate and remain a silvery grey.

During their journey they have to overcome strong currents, rapids, weirs and other obstacles as the spawning grounds are located in the upper reaches of rivers in clean and well oxygenated waters. Here the females excavate large hollows (called redds) in which they deposit their eggs which the males fertilize; after which they are covered with gravel. During migration they do and therefore many die after spawning through sheer exhaustion. The young salmon stay in the river for two to three years and only then migrate to sea. They live in the sea one to three years and grow very fast. In freshwaters they feed on small invertebrates, but in the sea solely on fish.

Salmon migrate en masse to spawn in the European rivers extending from the mouth of the Pechora to the rivers of north-western Spain. They are also very numerous in the rivers of Iceland, Greenland and along the Atlantic coast of North America, southwards to the Hudson River. However, during the last century they have become scarcer in a number of European and North American rivers as a result of the construction of irrigation and dam installations and the progressive pollution in the lower rivers and have even disappeared in some.

The body of the salmon is spindle-shaped, its head is relatively small, its caudal peduncle is quite thin and longer than the anal fin. The caudal fin is slightly curved. Young salmon, which hatch in spawning grounds in the upper reaches of rivers, usually depart for the sea after two to three years as smolts. Some, however, stay permanently in the river, where they mature sexually, but differ from the sea salmon in their colouring, which resembles that of the trout. They also have 9 to 10 large blue-grey spots on the sides, the parr-marks.

At the final stages of their return journey from the sea to the rivers, salmon are guided by the chemical composition of the water. Every river has for them its individual taste and smell, so that they never make a mistake and always go back to the river where they were born. In recent years artificial breeding of salmon has been developed in an attempt to counter the losses due to pollution and other factors. Now salmon fertilized eggs and young salmon arc put into the rivers in large quantities and so the stock of the salmon is constantly being replaced.

Maximum size and weight: 150 cm, 50 kg. Identifying characteristics: Gross- or star-shaped black spots scattered on the sides. Adipose fin plain grey. Upper jaw bone reaches only to the rear of the eye, section of the body in front of tail fin narrow.

Different Salmon species: Arctic Charr

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