The lowly earth worm, so familiar to fish on the end of a hook, is usually acceptable to all fresh water fish. These worms are generally too big to be fed as collected, and will need to be chopped or sliced.
An old pair of scissors does the job fairly well, or you are able to use two steel plates with circular grooves like a coarse file. The worm is rubbed between the two plates which soon shreds it. Clean earth worms well prior to shredding.
Nottingham red worms are the very best to use. Those that ooze a yellowish secretion should be thrown away. The fish won’t eat them anyway.