These are two completely different fish: the salmon trout, like the salmon, spends its adult life in the sea; the rainbow trout is confined to fresh water. However, their flesh is of a similar texture and any recipe for one will suit the other.
To look at, the difference between a salmon trout and a salmon is minimal and therefore it can be difficult to tell them apart, but their flesh is very different. The tail fin of the salmon also has a slight fork, whereas the salmon trout’s is straighter, and whereas the spots of the salmon tend to be confined to the area above the lateral line, the trout’s are not.