Oncorhynchus mykiss: The Rainbow Trout

If you didn’t know now is as good a time as any to find out, I am a habitual nerd. Admittedly the library is one of my favorite places to go and read, most scientific research about trout… So in the course of doing so, I picked up a book written by William F. and John W. Sigler.

So here is a little bit of knowledge from the book. The name Oncorhynchus means hooked snout, in reference to the nose of a migrating trout or salmon. The rainbow trout or Oncorhynchus mykiss is one of the most widely distributed fish in the world including Hawaii, south Asian, New Zealand and Tasmania. Their native range extends from Rio del Presidio in Durango, Mexico to north of the Kuskokwim River in Alaska (Behnke, 1979).

Rainbow trout typically are spring spawners, however, stocked fish have been reported to spawn during every month of the year. They emerge from the gravel at .0.4 to 0.6 inches and by the first summer may be 4 inches in length (Scott and Crossman, 1973). Naturally reproducing fish often first spawned between 2 and 3 years old in the spring when the water temps hit 50F. Some wild fish wait as long as 5 years to spawn for the first time, whereas stocked fish can spawn in some cases can spawn after one year. Nest building can occur both day and night in gravel that is between 0.1 and 4.0 inches in diameter.

Rainbows grow fastest in water temps ranging between 68 to 70F but can survive for short periods of time in temps between 78 and 82F.  Rainbow trout have been long believed to be short lived with few living past 5 years of age, however in 1976 fish from Eagle Lake, CA were sample up to 11 years old (Simpson and Wallace, 1978). Lake fish often outgrow stream dwelling rainbow trout, average size as follows from 1 to 7 years; 2.6, 4.7, 11.4, 17.1, 20.3, 23.2 and 28.0 inches.

Studies showed that stream dwelling rainbow trout were less likely to feed on other fish, becoming piscivorous at roughly 2 pounds, until then they fed primarily on invertebrates. Lake dwelling fish became piscivorous once they reached between 12 and 16 inches.

Derek Olthuis is a fly fishing photographer and videographer. He is passionate about sharing his love for fly fishing and exploring new water. He films for the IF4 Film Festival and runs Trout Academy in his spare time.

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