The rainbow trout (Oncorhynchus mykiss) is a species of salmonid native to tributaries of the Pacific Ocean in Asia and North America. A non native species of trout in Ireland has been successfully stocked to many Irish waters mostly to put and take managed fisheries ​. This species of trout has very similar habits to the brown trout.Coloration varies according to habitat; in acid waters, greenish on the back, with a vivid rosy flush on the gill cover and along the side; in alkaline waters, rainbows are more silvery and the bar long the side is, at most, slightly pink; black spots only, absent from cheek and gill-cover and also, for the most part, along the mid-line of the sides; tail fin heavily spotted; sometimes faint spots on anal and pelvic fins also; in Irish waters, grows to about 4.5kg (9lbs) but much heavier fish are common at commercial put and take fisheries.