Some aquarists say there is a risk feeding Tubifex worms to aquarium fish, because they carry dangerous bacteria. Other aquarists believe there is only a very slight risk. Tubifex worms will eat whatever material there raised in. And most tubifex worms are raised in trout pond run-offs, therefore most tubifex eat fish manure. Which in my view means there an extremely high chance of passing on bacterial or parasitic infections feeding live Tubifex to your pet fish. But there is a happy ending to this story, frozen and freeze-dried Tubifex are safe and are available from local petshops.