This taxon is one of a number of benthopelagic species in the Amur River system. Benthopelagic river fish are found near the bottom of the water column, feeding on benthos and zooplankton
The persistence of mercury contamination in Amur River bottom sediments is a major issue, arising from historic cinnabar mining in the basin and poor waste management practises, especially in the communist Soviet era, where industrial development was placed ahead of sound conservation practises.
Other large benthopelagic river fish of the Amur Basin is the 200 cm yellowcheek (Elopichthys bambusa) and the 122 cm Mongolian redfin (Chanodichthys mongolicus)
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.
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.
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.
These fish are one of the most popular game fishes around the world, leading to nearly global introduction. They are introduced to stimulate local angling and associated recreational economies. However, where they are introduced, they can outcompete native trout species.
"In 1997, the first known magnetoreceptors -- directly linking magnetite to neural connections and activity -- were found in vertebrates. A team of zoologists from Auckland University, led by Dr. Michael Walker, had been studying this mysterious sense in trout, and knew that a region of its skull contained magnetite.
"Recording neural activity from that region, they discovered that a specific subgroup of nerve fibers within a branch of the trigeminal cranial nerve called the ros V nerve fired in response to changes in the surrounding magnetic field. They also found magnetite in a tissue layer directly beneath the trout's olfactory (smell) organs. When they injected a colored dye into the ros V nerve's newly exposed magnetosensitive fibers, the dye revealed that the fibers terminated and ramified all around the magnetite-containing cells within the trout's olfactory tissue." (Shuker 2001:46) Learn more about this functional adaptation.