Now that is an interesting fact. At what water temp does that peak out at?
Good question. It depends the species and whether is is a coldwater, cool water, or warm water species. There is a level where they become stressed and lethargic and oxygen levels aren't great (as you probably know the warmer water is the less oxygen it holds.) Of course trout become severely stressed when water temps go into the 70's especially brook trout unless there is significant natural or artificial aeration. But they still aren't fond of water temps I the 70's.
's.'s.
Here's something interesting I found raising smallmouth bass: Everybody assumes they are a coolwater species, but the ones I had in the pond were still active at water temps in the upper 80's to 90's. Several years ago I was feeding them in those water temps as that was the year we had air temps that hit 100 and above. And these were adult fish. The bluegills and yellow perch in the pond were no longer feeding on the pellets.
My larger yellow perch sulk on the the bottom when water temps get warm in the summer. Originally from Lake Erie stock. But then the pond is only 9 feet deep and I don't allow it to stratify.