Oncorhynchus mykiss (Walbaum, 1792)

Freshwater, brackish, or marine waters of temperate zones. The anadromous form, called steelhead, spawn and complete their early development in freshwater mountain streams, then migrate to spend their adult life in the ocean. In freshwater, they prefer cool water but have been known to tolerate water temperatures up to 24°C (native climates have water temperatures around 12°C in the summer). Productive streams have a good mixture of riffles and pools and overhanging vegetation for shade. Most importantly, they require gravel beds to lay their eggs, and therefore, are sensitive to sedimentation and channel scouring. Juvenile trout prefer protective cover and low velocity water and have been known to be swept away and killed in water that is too fast. Since they are native to the western U.S., then tend to be found in coastal streams and rivers which naturally have reduced flow in summer months.

Range elevation: 0 to 3000 m.

Range depth: 10 to 200 m.

Habitat Regions: temperate ; tropical ; saltwater or marine ; freshwater

Aquatic Biomes: pelagic ; lakes and ponds; rivers and streams; temporary pools; coastal ; brackish water

Female fish find suitable nest sites while their male mate guards the site from other interested males and predators. The female digs the nest (called a redd) with her anal fin and then descends upon it to position her vent and anal fin into the deepest part of the redd. The male joins her in a parallel position so that their vents are opposite each other. The male and female open their mouths, arch their backs, and deposit the eggs and milt (fish sperm) at the same time. The eggs are enveloped in a cloud of milt and are fertilized. Only a few seconds elapse from the time the female drops into the redd and fertilization occurs. The female then covers the nest with gravel and repeats the process again a few times until she has deposited all of her eggs.

Mating System: polygynous

Adult rainbow trout and steelhead lay their eggs in a series of nests in gravel. Collectively, the nests are called a redd. When they hatch, the hatchlings are still attached to, and survive on their yok sac. They remain in the protective gravel for about 2 to 3 weeks when they have shed their yolk sacs and are fit enough to survive in the open water. Juvenile fish tend to stick to shallow and side areas of the streams where there is protective cover and slow-moving currents. The remain in their native streams for 1 to 3 years while they grow fit enough to spawn or migrate to the ocean, in the case of steelheads.

Breeding interval: Rainbow trout breed every three to five years. Though steelhead are one of the only salmonids able to spawn twice in a lifetime, the return rate is very low, about 10-20%

Breeding season: Spawning occurs from March to July, depending on temperature and other climatic variables. Winter steelhead in California start spawning as early as January.

Range number of offspring: 200 to 8000.

Range time to hatching: 3 to 16 weeks.

Range time to independence: one to three years.

Range age at sexual or reproductive maturity (female): 3 to 11 years.

Range age at sexual or reproductive maturity (male): 3 to 11 years.

Key Reproductive Features: iteroparous ; seasonal breeding ; sexual ; fertilization (External ); oviparous

Average number of offspring: 3500.

Female rainbow trout and steelehead simply lay their eggs in a gravel bed and leave the young hatchlings to mature on their own. Male steelhead frequently breed with multiple female partners, possibly because more females than males die during the breeding period.

Parental Investment: no parental involvement; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Protecting: Female); inherits maternal/paternal territory

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Epitheliocystis. Bacterial diseases