This is one of my male guppies in a 20 gallon tank. This is the second guppy i have had that has had this long narrow piece of their tailfin come off. I have a few fake plastic plants in the aquarium and 2 of them appear to have sharp edges. None of the other fish in the tank (2 male guppies, dwarf gourami, gold dust molly, 5 harlequin Rasboras) have ever shown signs of aggression and have always been peaceful. Are there tails being cut by the fake plant?