BiologyAtlantic salmon is an anadromous species; broodstock spawn in freshwater, with juveniles migrating to sea at the smolt stage to grow before returning to spawn. Domesticated rainbow trout in Tasmania are a non-smolting strain with large juveniles rather than smolt being introduced to the sea. Natural populations of non-smolting species remain in freshwater.
BroodstockIn wild populations, brood females excavate a shallow hollow (redd) in a substrate of small rocks, cobbles, gravel and sand. Males and females spawn together in the areas of streams and rivers, releasing eggs and milt simultaneously.
EggsFertilised eggs which have fallen into the redd are then covered with substrate by the tail movements of the female. Spawning occurs during autumn and winter. Atlantic salmon spawn between autumn and the middle of winter with spawning occurring over a shorter duration than rainbows which may spawn between autumn and spring.
AlevinsEggs remain buried in the substrate for up to 2 months before hatching into sac fry called alevins, which draw nutrients from the attached yolk sac for a few weeks.
FryOnce most of the yolk is absorbed, the fry emerge from the substrate in search of food, such as invertebrates.
ParrThe fry grow into small juveniles called parr which display characteristic "fingerprint" markings on their flanks.
SmoltParr continue to grow in freshwater until the smolt stage when they migrate to the sea to grow, or they complete the cycle in freshwater. Salmonids are able to complete their entire life cycle in freshwater, but sea-run stock must return to freshwater to spawn.
Grilse, SalmonSalmon, which return to freshwater after one winter in the sea, are referred to as grilse while the term salmon is normally used in reference to two+ sea-winter fish.
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