Oncorhynchus mykiss (previously Salmo gairdneri) are native to North America and have been known to reach 1.2 metres in length and 18 kilograms.
New South Wales was the first Australian state interested in obtaining rainbow trout and the first ova arrived on 7th August 1894 from the Wellington Acclimatisation Society in New Zealand. These were first hatched in troughs set up in an abandoned blacksmith's shop below the Prospect Dam which was at that time Sydney's main domestic water supply and the site of Fisheries first permanent hatchery.
The upper body of rainbow trout varies from bluish green to silver on top, heavily marked with small black spots. The belly is silver white. They are called rainbows because of their magnificent crimson lateral stripe and the rainbow colours which are displayed during the spawning months (over late winter and spring). During spawning time males can become very dark in colour. Males (bucks) are longer in the nose than females (hens) and will develop lumps on the lower jaw which will grow large enough to form a hook in later years. Flesh can vary from white (diet of insects) to orange (diet of crustaceans such as Daphnia).
Rainbow trout are carnivorous and feed mainly on insect larvae, adult insects, molluscs, worms, small fish and crustaceans. The rainbows's speed is legendary. Fly fishermen should be careful not to miss the 'take' and during the retrieve to react quickly when the fish hits the fly at a speed that may break the leader. On catch-and-release waters (such as Uncle Billy's Retreat) they can become fussy, which calls for fine tippets, good presentation, and flies that 'match the hatch'. The surface and sub-surface are its preferred hunting grounds.