The marine form of Salvelinus fontinalis differs in colour from the freshwater form, losing its distinctive speckled markings and taking on a more silvery colouring.
When brook trout (also known as speckled trout) exhibit anadromous behaviour, they are called “sea-run brook trout” or simply “salters.” They are the most sought after species in many areas.
- Taxonomy -
- Salvelinus fontinalis Linnaeus, 1758
- Common name
- Sea-run brook trout, brook trout, speckled trout, salters
- Physiology -
The body of sea-run brook trout is elongated (20 to 30 cm), fusiform and laterally compressed.
The skin of sea-run brook trout varies in colour depending on the age of the fish and the environment where they are found.
- When at sea, the fish have mottled olive green, almost black backs. The flanks are paler and have small red spots with blue halos.
- When in the river, sea-run brook trout are darker, losing their silvery-blue sheen.
- During the spawning season, their colouring is brighter and the males’ bellies turn orange.
- Feeding -
Brook trout are carnivorous, with a diet that varies widely depending on the available prey, including crustaceans, insects, spiders, small fish and worms. Cannibalism of eggs and young fry has also been observed
- Life cycle -
Le cycle de vie de la truite de mer peut être décomposé en 3 phases qui vous sont présentées ci-dessous :
Returning to the river
Adult sea-run brook trout migrate long distances – sometimes extremely long – to reach their natal river. Spawning occurs in the fall in rivers, streams and lakes where the water is cold and shallow, and gravel covers the bottom.
Selecting the spawning grounds
Brook trout seek spawning grounds with shallow, cold water and a gravel bottom, whether in lakes or streams.
Once in the spawning area, the females look for the best spot to deposit their eggs. The males, now sporting bright orange bellies, become more aggressive to defend their territory around a female.
Preparing the redd
Female chooses a place for one or more redds, and digs the shallow depressions by lifting the gravel with her tail.
SpawningDuring spawning, the male and female are positioned side by side. The male’s whole body shakes or quivers as he stretches and gapes. Thus stimulated, the female does the same. When the quivering subsides, the female deposits her eggs and the male fertilizes them by releasing his milt.
Protecting the eggs
The female covers the eggs with gravel to protect them from predators. Depending on her size, a female sea-run brook trout will deposit 100 to 5,000 eggs measuring 3.5 to 5 mm in diameter.
Returning to the sea
After spawning, sea-run brook trout can return downstream to the sea, and some will come back to the river once or twice more to spawn in subsequent years.
Growth in fresh water
The eggs deposited in the fall will develop under the gravel all winter, oxygenated by the water constantly flowing through the gravel bed. However, in addition to predators, many dangers await the eggs: fungi; fine sediments filling the interstices between the gravel; freezing of the eggs; and scraping of the riverbed by ice.
In early May, the eggs hatch, releasing the yolk-sac fry or alevins. They burrow a little deeper into the gravel, which keeps them safe from being carried away by ice scraping the bottom of the riverbed during the spring break-up. Three weeks later, the fry emerge from the gravel and begin to feed on small insect larvae.
The first year of growth
During the first year, young brook trout acquire the ability to swim in the current. It is probably at this time that the future anadromous form differentiates from the resident form. The anadromous form seems to prefer the faster currents while the resident form prefers the sills around the pools. No visible morphological differences between the two forms appear until after the first summer, when certain changes occur: the brook trout preparing to migrate are more slender than the residents and their pelvic and pectoral fins are shorter, allowing them to swim better when migrating at sea in large schools.
La croissance en mer
In mid-May, the anadromous brook trout over one year of age descend the river to begin their migration at sea. The smallest of them will wait until they are two years old to be large enough to survive predation and the rigors of osmoregulation (adaptation to life in salt water).
Migration at sea
After their downstream migration, the young brook trout move into open ocean. During the first year at sea, 90% of these young fish will die. But for those who survive their time at sea, the benefits of the abundant food resources are impressive. Feeding at sea allows the brook trout to grow very rapidly, from an average length of 11 centimetres when they migrate downstream to an average of 20 centimetres at the end of the summer.
Return to natal rivers
In the fall, with the onset of cold weather and the increased salinity of the surface waters, the young brook trout return to their natal river to breed. Guided by ocean currents and other mechanisms that remain obscure (stars, magnetic fields), they approach their natal river where the scent finally guides them home
Capable of spawning several times
The majority of sea-run brook trout die after spawning, with only about 30% of spawners surviving until the following spring. These hardiest spawners, however, can reproduce for several consecutive years and thus ensure the survival of the species.