Knowing the anatomy of a fish and its feeding tendencies are worthy bits of information
A tarpon pod swimming in 4-feet of water will never see your fly in 8-feet of water. A bonefish feeding on crabs will not see your bead chain Crazy Charlie sitting on the surface.
Lefty Kreh has said many times: “A fish’s anatomy and feeding behavior substantially dictate were in the water column you should offer the fly.”
That said, a bonefish will take an offering on the surface as will a bottom feeding redfish. The later sometimes a sucker for a ‘gurgler’.
The position of the fish’s eyes and mouth orientation are true indicators of their feeding profile.
A trout feeding on nymphs crawling on rocks will not likely rise to your surface floating presentation.
Understanding the depth and feeding preferences of your quarry will greatly improve your hook up stats.