They aren't the kind in the water. Enchytraeus albidusis the latin name. another type would be Enchytraeus buchholzi or Grindal worms which are slightly bigger than the white worms. In either case some aquarists will make cultures (container with dirt and a piece of bread soaked in water,/milk or yogurt is what is normally used, but i'm sure you can feed the worms other things) of these worms to feed their fish and small fry.