Yep bottom feeders, that explain the sucker mouth. I am pretty sure they are a relative of some kind to carp; and probably not too distant.

They are the first fish (at least up here) to spawn in the Spring, so with the high water and runoff everywhere, the scoot out of the lakes and up the ditches in the fast water. This is what is called the 'run' not too different than a Salmon run.

This is when many people head out with nets and waders and scoop them up, or they can be taken with Archery equipment too. it's also not uncommon to see people in the ditches with pitch forks.

Following the suckers, are the Jackfish and then Walleye run, but both of those are considered gamefish, and not legal to dipnet.

I got 24 pints and 4 quarts of fish canned last night, under 4 different recipes, and have about another 8-10 jars to do tonight.
They are typically a pretty bland tasting fish, so they will take on whatever flavours that you give them.