Oncorhynchus mykiss (Walbaum, 1792)

Oncorhynchus mykiss View in CoL View Figure

Common name. Rainbow trout.

Diagnosis. Distinguished from species of Salmo by: ● wide, pink to red stripe from head to caudal base (except in sea-run form) / ● caudal with black spots at least on upper lobe, usually on whole fin. Size up to 1000 mm SL.

Distribution. Widespread or stocked from fish farms, especially in Türkiye and Iran. Unclear where established. Native to Kamchatka and south to lower Amur drainage and Pacific basin of North America south to northern Mexico.

Habitat. Stocked in cold lakes, rivers, and streams. Usually not stocked in water with summer temperatures above 25°C or in ponds with very low oxygen concentrations. Spawns on gravel in fast-flowing water.

Biology. Anadromous, lacustrine, and resident forms. Often spawns first time at 1 year, 3–5 years in north, usually in February–May when temperatures rise above 10–15°C. Farmed trout mature August–April, depending on strain. Makes short spawning migrations. Anadromous and lake forms may undertake long migrations to spawning streams. Females build redds in gravel bottom of moder- ate to fast-flowing streams or rivers. Breeding populations will not be established if peak juvenile emergence coincides with flood season and cold summer temperatures, and if temperatures do not fall below 13°C. In agonistic behaviour, O. mykiss fry dominate Salmo fry of similar size, and juvenile and adult Salmo dominate similar size rainbow trout. Feeds on a wide range of aquatic and terres- trial invertebrates and small fish. At sea, feeds on fish and cephalopods. Feeding is negligible below 5°C and above 25°C water temperature.

Conservation status. Non-native; introduced for recreational fisheries and as escapees from fish farms.

Further reading. Smith & Stearley 1989 (systematics, nomenclature); Behnke 1992 (diversity); Stearley & Smith 1993 (phylogeny); Zelinsky & Makhrov 2001 (chromosomes); Fausch et al. 2001 (invasion success); Yoğurtçuoğlu et al. 2021c ( Türkiye).