[fishy]

No offense, but with all that experience with fish finders, I’m surprised you’d think a fish arch would appear noticeably different from one freshwater species to another (other than big arch = big fish, little arch = little fish). All you can do with today’s technology is to go fishing and learn as much as you can about the tendencies of certain species to appear in certain places at certain times on a certain body of water. Unless of course you invest in a good underwater camera.