Mainahs70,
I stocked rainbow and brookies October 2021. The hatchery raised both from eggs at the same time. The rainbow were 10-12 inches and the brooke trout were about 6 inches when I purchased them. Now almost 6 months later it is easy to tell them apart. The rainbow trout are so much larger attacking the feed like piranhas making a huge splash. The brooke trout feed is less aggressive with a smaller splash because of their size. Many times I am able to see both species breach the surface or a tail whip throwing a splash. I hope this helps!