While watching Tv this morning i noticed that one of my orange and black tetras was swiming in circles.She was swiming fine then suddenly began swiming in circles,upside down and on her side.Its like she can only use one fin.Her tail fin is aimed somewhat downwards......it just curves down...just a tad.She is still eating and i have put her in a cup, away from the other fish.i have no quarentine tanks.I was wondering........is something wrong with her swim blatter..parasite...or could she have been damaged by another fish.....broken tail?