Salmon

The Salmonidae family includes the genera Salmo, Oncorhynchus, and Salvelinus, comprising the salmon, trout, and char. Atlantic salmon have been held in culture for release in rivers since the 1800s, and in a farming situation for food production since the 1960s. Atlantic salmon make up the greatest part of the world production of the various salmon species, 1,025,287 T in 2001.[1] Four countriesNorway, Chile, the United Kingdom, and Canada-produce almost 90% (Fig. 1), the rest being produced by eight other countries. Of the Pacific salmon species, the production of coho salmon (Oncorhynchus) (151, 386 T in 2001) is greatest, 90% of it being produced by Chile (Fig. 2).[1]

The production of Atlantic salmon has increased as a result of greater numbers of fish being farmed using continuously improved genetic material, nutrition, and man-

agement. The cost of production per kg round weight (not including slaughter and packaging costs) in 1997 was US $2.495 in Norway and US $1.986 in Chile, the main differences being smolt costs and undefined miscellaneous costs.[2] Feed (including pigments, vitamins, medication, and feed transport) accounted for 51% of the production costs in Norway and 61% in Chile.[2] In 2001 in Norway, 306,328 kg salmon were produced in the sea-phase per man-year, a 58% increase from 1997.[3]

LIFE CYCLE

Most salmon are anadromous. In the wild, spawning, fertilization and hatching of roe, and an initial growth period occur in rivers. This is followed by migration to sea and the main growth period, and later, as mature fish, migration back up the river to reproduce. This cycle is duplicated in culture conditions. Mature Atlantic salmon are stripped for roe (eggs) and milt (secretion containing the sperm), these are mixed to allow fertilization, and then the eggs are hatched, all in fresh water. The alevin (young fish) lives off its yolk sac until it has developed enough to be able to consume exogenous feed. Growth continues in freshwater tanks until the fish has undergone a physiological transformation, smoltification, allowing it to survive the hyperosmotic conditions of salt water. With artificial light regimes and good husbandry, the smoltification process may be started early so that smolt are produced during the first autumn, although usually this process occurs later and the fish are not transferred to sea cages until the second spring. Atlantic salmon grow to a market size of 3 to 5 kg during a period of about 9-12 months in the sea. Fish chosen for broodstock are moved back to fresh or brackish water a few months before spawning.