It's probably a strain of rainbow trout,
Oncorhynchous mykiss
As Naiad said, stay away from any form of salmonid if you have a small pond.
I have dealt with trout farmers who have heart failure when the temperature rises in summer, they need deep, cool, well oxygenated water. You only have to look at a salmonid the wrong way and it goes belly up.
They can be kept in aquaria when small, they will grow big and eat any smaller fish.
I do like the look of trout, especially on a plate with new potatoes and steamed green beans
