After a fine summer spent in the lake, the lake trout return to their native streams to give a new generation the opportunity to be born. Spawning, or reproduction by the female trout, begins as soon as the days get shorter and cooler. After long and meticulous research, a strategic site is chosen, sheltered from light and predators. The site should be made up of gravel and pebbles, neither too fine nor too thick. Water must be able to circulate abundantly around the eggs, so that they have the oxygen they need without being washed away by high water.
To begin spawning, the trout performs a highly acrobatic choreography; it has to lie on its side, with its flank facing the stream, flicking its tail to remove any sediment that is too fine. In this way, a spawning ground consisting of a dome downstream and a pit upstream is formed and can accommodate the eggs. Before the eggs are laid, the male finally steps in - and often all the males! The eggs are fertilised by one or more males, who battle for territory by constantly courting the female. The number of eggs produced by a female depends on her weight and can vary between 250 and 2,000! Once the eggs have been laid and fertilised, the female again wags her tail over the substrate to gently place a little gravel on top of the eggs to protect them. Weakened by this hard work, the trout will generally leave the spawning ground and move downstream to a more suitable feeding area.
This is how the young fry are born, with the quality of the spawning site chosen by their mother influencing their development.
Information taken from the information brochure published by the Swiss Fishing Advisory Board FIBER.
For further information: Trout in Switzerland
