Often when I buy tubifex worms to feed to my fish they have other things besides tubifex worms in them. They look like flukes or leaches to me. Are they alright to feed to my fish or should I pick them out? I've been feeding live food for quite a while and haven't had any problems yet, but I wanted to get other peoples opinions. What are these things anyway? There are at least two kinds, the white flat elongated football shaped ones and the longer thinner white ones.