This is all very interesting stuff.
I wonder how much this relates to beneficial bacteria in the stomach/gut of the fish? Depending on the water type, genetics, food sources, climate, etc. I wonder if the same species of fish in different ponds may possess quite different flora in their digestive tract to help them absorb a particular diet under certain conditions?
What may be present in southern ponds, may not thrive in northern ponds, which may explain some differences in eating patterns. Since fish are so good at moderating their internal PH and such vs the water they are in, who is to say they cannot somewhat influence the chemistry of their innards to favor a type of flora to digest a food source available to them? It may take them time to adjust this, and thus fast temperature swings and water chemistry cause a drop in appetite as they are playing catch-up internally?
Just thinking out loud, but I think a lot is misunderstood about the role of beneficial bacteria in most animal's guts and how it interacts with health.
My perch would love to eat right up to ice over, maybe even after. I stop at 50 degrees, but they are quite active even under the ice. I always thought they floated around like logs until I got my underwater camera down there and took a look. They were clearly actively hunting for food and curious about the camera.
