Was wondering if they do. I recently bought 1lb of black worms and noticed there were baby leeches on my glass tank. Ive been tacking them out with a sponge and letting them dry out.
^^Yep - that's why anglers use them as bait! But, to answer the question - yes they do latch on to fish or anything else that has blood in it! Leeches do "swim" and search for hosts to latch onto, so I would keep an eye on your fish. If they eat the leeches, great!