I have a tropical, fresh water fish tank and during one of my routine cleanings of it I noticed that after I had vacuumed the bottom of the tank I had these little guys floating around in the water. I have never seen insects like these before and am just curious as to what they are and if they would be harmful to the fish I have in my tank. I have attempted to remove as many as I can find, just to be on the safe side.
These are immature (naiads/nymphs) of a damselfly. They are general predators on other aquatic life, mostly insects, but also occasionally small tadpoles and minnows -
http://www.uky.edu/Ag/CritterFiles/casefile/insects/damselflies/damselflies.htm
