Harlequin Rasbora with one white pectoral fin

[Country joe]

As above, I'm useless with a mobile camera, and it swims too fast, it has one white pectoral fin, it is swimming okay along with its mates, and eating, any idea what it could be, and how to treat?

 

[Country joe]

I've just noticed a green neon tetra, rubbing itself on a leaf, have noticed a black neon tetra doing this yesterday on a piece of wood, but not seen any signs of white spots.