You can use any size bluegill, green sunfish etc as bait. Where it gets sticky is bluegill, green sunfish, creek chubs etc over 5 inches long fall in the "all other species combined" category. The limit is 50 for these larger fish. It's 150 for fish under 5". This is for large reservoirs. In smaller MDC lakes the fish over 5" limit is 20 and there is no cast netting or trapping except for shad. Shad, carp, silver carp, bighead carp have no limits regardless of size. AS far as how you catch the bait, it depends on the body of water. But basically if you can trotline, you can collect bait too.