---
title: "What the sources say about the Rainbow Trout | AnimalTracks.wiki"
description: "44 claims from the Rainbow Trout profile, each beside the words of the source that backs it."
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# What the sources say about the Rainbow Trout (*Oncorhynchus mykiss*)

> 44 claims from the Rainbow Trout profile, each beside the words of the source that backs it. A "..." marks a cut in a quote and [brackets] an insertion.

Profile: [Rainbow Trout](https://animaltracks.wiki/animals/rainbow-trout/)

## Hammerson & Bogutskaya (2024). Oncorhynchus mykiss. The IUCN Red List of Threatened Species 2024: e.T166481A18229476.

https://doi.org/10.2305/iucn.uk.2024-2.rlts.t166481a18229476.en

| The page says | The source says |
| :--- | :--- |
| Least Concern | IUCN Red List category: Least Concern (LC). (note: Assessed 2020 (IUCN taxon 166481); category read through GBIF's copy of the Red List.) |
| The Red List rates the species Least Concern. | IUCN Red List category: Least Concern (LC). |

## Yano et al. (2012). An Immune-Related Gene Evolved into the Master Sex-Determining Gene in Rainbow Trout, Oncorhynchus mykiss. Current Biology.

https://doi.org/10.1016/j.cub.2012.05.045

| The page says | The source says |
| :--- | :--- |
| A stream fish whose sex is set by a Y-chromosome gene unrelated to any known sex-differentiating gene. | sdY is a novel vertebrate master sex-determining gene not related to any known sex-differentiating gene |
| One gene, sdY, decides whether it becomes male or female | The targeted inactivation of sdY in males using zinc-finger nuclease induces ovarian differentiation, and the overexpression of sdY in females using additive transgenesis induces testicular differentiation. |
| it is expressed only in the testis | an unknown gene expressed only in the testis |
| The sdY gene is a vertebrate master sex-determining gene not related to any known sex-differentiating gene. | sdY is a novel vertebrate master sex-determining gene not related to any known sex-differentiating gene |
| sexually dimorphic on the Y chromosome | This gene, named sdY for sexually dimorphic on the Y chromosome |
| Researchers who switched it off in males, using a tool called zinc-finger nuclease, got fish that grew ovaries. | The targeted inactivation of sdY in males using zinc-finger nuclease induces ovarian differentiation |
| Researchers who added sdY to females got fish that grew testes. | the overexpression of sdY in females using additive transgenesis induces testicular differentiation |

## Thomas, Allain & Owen (2021). Predation and ingestion of a barred grass snake Natrix helvetica by a rainbow trout Oncorhynchus mykiss in Lot, France. Herpetological Bulletin.

https://doi.org/10.33256/hb156.4041

| The page says | The source says |
| :--- | :--- |
| In 2020 a trout of about 30 centimeters was caught in a small French stream. | At around 16:00 h on the 18th July 2020, a rainbow trout, recently released for the purpose of recreational fishing, was caught by HO while angling along the Saint-Matré (a small stream) in Grézels, Lot, France (note: The 30 cm figure is quoted in the claim 'a trout of about 30 centimeters' (The fish was a mature specimen, roughly 30 cm long).) |
| a trout of about 30 centimeters | The fish was a mature specimen, roughly 30 cm long. |
| Inside it was a live hatchling grass snake about 20 centimeters long. | a live hatchling barred grass snake was found inside the gastrointestinal tract (Fig 1). The hatchling snake measured approximately 20 cm long |
| what evidence there is suggests fish rarely eat barred grass snakes, and only small ones | What evidence there is suggests that the consumption of N. helvetica by fish is rare and restricted to small specimens. (note: 'Only small ones' is the source's 'restricted to small specimens'.) |
| An angler in France gutted a trout of about 30 centimeters and found a live hatchling grass snake inside it. | The trout was gutted minutes after capture and surprisingly, a live hatchling barred grass snake was found inside the gastrointestinal tract (note: The 30 cm figure is quoted in the claim 'a trout of about 30 centimeters' (The fish was a mature specimen, roughly 30 cm long).) |
| The authors say the evidence suggests fish eating these snakes is rare. | What evidence there is suggests that the consumption of N. helvetica by fish is rare and restricted to small specimens. |

## Oncorhynchus mykiss (Walbaum, 1792), Rainbow trout. FishBase.

https://www.fishbase.se/summary/Oncorhynchus-mykiss.html

| The page says | The source says |
| :--- | :--- |
| Clear, cold headwaters, creeks, rivers and lakes of the Pacific Slope of North America, now introduced widely | Inhabit clear, cold headwaters, creeks, small to large rivers, lakes, and intertidal areas |
| Aquatic and terrestrial invertebrates and small fishes | Feed on a variety of aquatic and terrestrial invertebrates and small fishes. |
| Their native range runs down the Pacific Slope, from the Kuskokwim River drainage in Alaska to the Otay River drainage in California. | Pacific Slope from Kuskokwim River drainage in Alaska to Otay River drainage in California, USA. |
| FishBase gives a common length of about 60 centimeters. | common length : 60.0 cm TL |
| They feed on aquatic and terrestrial invertebrates and small fishes. | Feed on a variety of aquatic and terrestrial invertebrates and small fishes. |
| At spawning time the female digs a pit in the gravel while a male courts her or drives other males away. | The female finds a spot and digs a pit. While digging, an attendant male courts her or is busy driving away other males. (note: 'In the gravel' is ADW's: 'Adult rainbow trout and steelhead lay their eggs in a series of nests in gravel.' ADW's 'digs the nest with her anal fin' was cut: salmonid females dig with the tail, and FishBase names no fin.) |
| A female makes 700 to 4,000 eggs per spawning event. | Females produce from 700 to 4,000 eggs per spawning event |
| Rainbow trout are often hatched and stocked into rivers and lakes, especially to attract recreational anglers. | Cultured in many countries and is often hatched and stocked into rivers and lakes especially to attract recreational fishers |
| now introduced widely | Widely introduced and established in Canada and USA |
| FishBase gives 60 centimeters as a common length. | common length : 60.0 cm TL |
| Its record is 123 centimeters, and the heaviest published weight is 25.9 kilograms. | Max length : 123 cm TL male/unsexed; (Ref. 120611 ); common length : 60.0 cm TL male/unsexed; (Ref. 5504 ); max. published weight: 25.9 kg (note: 'Record' is FishBase's max length; 'heaviest published weight' is its max. published weight.) |
| FishBase lists them as widely introduced and established in Canada and the USA, and elsewhere in the world. | Widely introduced and established in Canada and USA, including Arctic, Atlantic, Great Lakes, Mississippi River, and Rio Grande basins, and elsewhere in the world |
| It says several countries report adverse ecological impact after introduction. | Several countries report adverse ecological impact after introduction. |
| FishBase lists a maximum length of 123 centimeters, a maximum published weight of 25.9 kilograms and a maximum reported age of 11 years. | Max length : 123 cm TL male/unsexed; (Ref. 120611 ); common length : 60.0 cm TL male/unsexed; (Ref. 5504 ); max. published weight: 25.9 kg (Ref. 120611 ); max. reported age: 11 years |
| Rainbow trout live in clear, cold headwaters, creeks, rivers, lakes and intertidal areas. | Inhabit clear, cold headwaters, creeks, small to large rivers, lakes, and intertidal areas |
| with another native population on Russia's Kamchatka Peninsula | Eastern Pacific: Kamchatkan Peninsula (note: FishBase continues: records outside Kamchatka 'probably represent migrating or straying Kamchatkan steelhead ... rather than the established native population'.) |

## Steelhead Trout. NOAA Fisheries.

https://www.fisheries.noaa.gov/species/steelhead-trout

| The page says | The source says |
| :--- | :--- |
| NOAA calls steelhead a unique life-history type of rainbow trout | Steelhead are a unique life-history type of rainbow trout. |
| the ones that go to sea typically grow larger than the ones that stay | Steelhead (anadromous rainbow trout) that migrate to the ocean typically grow larger than the individuals that remain in freshwater. |
| Steelhead can reach about 30 pounds (roughly 14 kilograms) | Up to approximately 30 pounds (note: Metric figure is a conversion.) |
| NOAA says they live up to 11 years, usually 5 to 8. | Up to 11 years, though usually 5 - 8 years (note: Quick Facts figure is for steelhead, the sea-run form.) |
| along the West Coast, 11 steelhead populations are protected under the Endangered Species Act | Along the West Coast, 11 species of steelhead are protected under the Endangered Species Act (note: NOAA's '11 species' are the Distinct Population Segments it lists, which the ESA treats as species; page last updated 09/24/2026.) |
| Some rainbow trout stay in fresh water all their lives. | Those that stay in fresh water all their lives are called rainbow trout (nonanadromous). |
| Others migrate to the ocean and come back to spawn, and those are called steelhead. | Steelhead (anadromous rainbow trout) that migrate to the ocean typically grow larger than the individuals that remain in freshwater. They then return to freshwater to spawn. |
| A steelhead is a rainbow trout that heads out to sea. | Steelhead (anadromous rainbow trout) that migrate to the ocean |
| Unlike most other Pacific salmonids, the group that includes salmon and steelhead, they do not necessarily die after spawning. | Unlike most other Pacific salmonids (i.e., salmon and steelhead ), steelhead are iteroparous, meaning they do not necessarily die after spawning |
| Trout that stay in fresh water all their lives keep the name rainbow trout, and the sea-going ones typically grow bigger. | Steelhead (anadromous rainbow trout) that migrate to the ocean typically grow larger than the individuals that remain in freshwater. (note: 'All their lives' is NOAA's: 'Those that stay in fresh water all their lives are called rainbow trout (nonanadromous).' (claim 'Some rainbow trout stay in fresh water all their lives.')) |
| and 40 inches (about a meter) | Up to approximately 40 inches (note: Metric figure is a conversion; steelhead Quick Facts.) |
| Some rainbow trout stay in fresh water all their lives, while steelhead migrate to the ocean and then return to spawn | Those that stay in fresh water all their lives are called rainbow trout (nonanadromous). Steelhead (anadromous rainbow trout) that migrate to the ocean typically grow larger than the individuals that remain in freshwater. They then return to freshwater to spawn. |

## Oncorhynchus mykiss, Coast rainbow trout. Animal Diversity Web, University of Michigan Museum of Zoology.

https://animaldiversity.org/accounts/Oncorhynchus_mykiss/

| The page says | The source says |
| :--- | :--- |
| where they are introduced they can outcompete native trout species | where they are introduced, they can outcompete native trout species |