Any fish that will eat a minnow or a worm/nightcrawler will eat a leech. It's natural forage and a solid bait for bream, smallmouth, LM, crappies and sauger/walleye. I've bought leeches pretty exclusively for 15 yrs - uh, Up North and always slayed the walleyes and smallies on them. Use those artificial ones as you would a real one - bare #4 hook and a shot up 14 inches or tipped on your favorite 1/16th or 1/8 in heavy current jig head. Great bait. Don't under estimate it.