Not long ago, I found a sizeable rainbow trout rising. He was sipping Pale Morning Dun mayflies, and appeared to me to be quite discerning in his taste. Each natural that drifted by was subject to intense scrutiny; many were rejected outright. I thought it might be fun to photograph this fish as it fed, and after a careful stalk I settled in with my camera. Almost at once, a large object came floating into view. Through the lens I didn’t think it resembled an insect, yet it caught the trout’s attention immediately. Floating nearer to him, I took it to be a dead leaf, or part of a leaf.
The fish apparently thought otherwise. Per his routine, he wafted up, gave close inspection, and took the object confidently. At that point I figured I’d made a mistake in identification, and wondered just what kind of insect it was. But later that day while reviewing my photographs, I discovered that the trout had rather quickly ejected the item, apparently after realizing it wasn’t food. You can see this in the fourth photograph.
Longtime anglers all know that trout often take unusual objects (our flies included). That they might confirm what constitutes food by using taste and/or feel in addition to vision seems logical. No different than us, really. It’s just harder to see in the liquid realm that trout inhabit.