Salmon are an anadromous species — starting life in freshwater, migrating to the ocean to feed and grow, and returning to their river of birth to spawn. Most salmon go through distinct stages:
Ova: In late autumn, female salmon dig channels (redds) in the (freshwater) riverbed gravel using their tails and release hundreds of eggs for the male to fertilise with his milt (sperm).
Alevin: hatch in spring and remain in the gravel, feeding off their yolk sacs as they develop into fry. Depending on the water temperature, they emerge from the gravel after 4 to 6 weeks with seven fins and, of course, a tail.
Fry: Having absorbed the yolk sacs, the fry leave the redds to hunt for food. They grow quickly during their first year, feeding on microscopic organisms.
Parr: From one-year old, the fish are known as parr (photo below). Their fingerprint markings, with orangey-red dots between, act as camouflage. They stay in freshwater for one to four years.
Smolt: Change is afoot as the process of ‘smolting’ or ‘smoltification’ begins. It’s a complex physiological transformation, during which salmon become able to osmo-regulate. This allows them to excrete excess salt and adapt from freshwater to saltwater environments. In freshwater, parr accumulate body salt, which is one reason behind their urge to head out to sea. With their new capability to excrete salt, the smolt migrate to the west coast of Greenland, off the Faroes, Iceland and into the North Norwegian Sea to feed on their staple diet of capelin, squid, shrimp as well as herring, sand eel, sprat and krill.
Adult salmon: After one to three years at sea, salmon return to the same rivers where they were born. It’s one of the great mysteries of nature how they do this, but smell (the chemical signature of a river, perhaps) is considered one factor. An astonishing journey!
At Tayinloan we need a freshwater hatchery to fertilise eggs and grow juvenile fish. After about nine months the smolt reach a weight of about 100g and are ready to transfer to the grow-out tanks, which will contain water at an ideal salinity, somewhat lower than seawater but still brackish. Nine months later, the smolt should have grown to 5kg salmon that are ready for market.