The ova hatch early in the year (January-February) feed off their egg sacks but do not leave the safety of their gravel redd until the spring when they emerge as fry and begin to feed independently. Juveniles can remain in freshwater for anywhere between 1-8 years before undergoing a challenging physiological transformation called smolting that allows them to migrate from freshwater into salt water. Smolts develop a silvery colour that distinguishes them from younger trout that are darker. The smolting process and resulting “smolt run” (groups of smolts moving downstream from their juvenile habitat to brackish water) occurs primarily in April-May in Skye and Lochalsh, however, the smolting and migration window for trout is often longer than it is for salmon and some smolts have been shown to enter the marine environment through the summer and autumn months.
Once in the marine environment, some trout will remain close to the shore while others will travel long distances in search of other feeding grounds. Research has shown that Scottish trout migrating to sea tend to stay in coastal areas near their natal river. Some trout will regularly move between fresh and salt water without spawning, and this behaviour has been linked to parasitic sea lice infestations which will vary depending on the individual. The amount of time trout remain in salt water before returning to freshwater ranges from a few months (finnock) to several years (multi sea winter fish).
Trout are often mistaken as salmon because they look similar, however they can be distinguished by a few key features. For example, trout are considered to be stouter than salmon with a thicker tail “wrist” and a shallower tail fork, their pectoral fins are smaller, and there are often marks below the lateral line.