When brown trout spawn, the male and female are not monogamous. These trout mate every year, and they are not likely to have the same mate year after year. Occasionally, large males take over a bed already occupied by a smaller, less aggressive trout.
Mating System: polygynandrous (promiscuous)
Brown trout mature at about 3 or 4 years of age. They spawn in the fall from October into December. When they spawn, they head into shallow headwater brooks of the river. The female scoops out a hollow on a gravel "redd" where she can lay her eggs. As she releases the eggs on the redd, the male simultaneously releases milt to fertilize them. The pair continues this process until all of the female's eggs are spent. The female then covers the fertilized eggs with sand or gravel for protection. The eggs are then left to develop and hatch the following spring. Browns do not necessarily come back to the same gravel bed to spawn each year, but they come back to the same general area of the river.
Key Reproductive Features: semelparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (External ); oviparous
Average number of offspring: 8000.
Female brown trout invest nutrients in yolk for eggs, but do not provide any care after the eggs are laid. Male brown trout provide no investment in offspring after fertilization.
Parental Investment: pre-fertilization (Provisioning)