Those are mosquito lava and your fish will love them. They are a great live food for young fish, however be careful when collecting live plants or anything else for that matter from out of the waters of the wild.

Another thing that likes to hide in the roots of small floating plants and on wild Ghost Shrimp is baby leeches. They will appear as a tiny black spot on the shrimp or your fish today and then tomorrow or the next day the spot is gone and you might see them swimming around like a snake or eel in the water. They are very hard to see when they are young because they are very small like a piece of black sewing thread.

Always wash any wild plants thoroughly and inspect them with a fine tooth comb (so's to speak...not like combing the desert in Space Balls, the movie) and keep them segregated in an aquarium by themselves for a week or so and check the water often for strange swimming critters. Nature is great as long as it remains outside.