I can attest to taking chub while fishing for bass. One of my favourite river areas for bass has been overrun by giant chub. Believe it or not some of these fish were over 2 pounds and a foot long. I couldn't believe it. They were striking on 3 inch+ Bass/Walleye plugs and anything else I tossed into the water. Now you rarely catch any bass at all in the area I speak of and most of these are small... seems the 'minnow' has lept its way to the top of the food chain with no larger predator fish. (Pike, Walleye) to eat them.
Kay, I have no doubt the fish you saw was likely a chub, they will eat just about anything a similar sized gamefish would.

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