Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.
17.625"
You have some math program that counts the spots and calculates the size of the fish?
It looks mature, or very close, owing to the full and rounded fins. It looks like a very small fish, compact in body size due to the extreme (far northern) location. I'll agree with Kurt on ballpark size, but change the units to inches, or even cm.