Rasbora borapetensis.... "brilliant" or "red tail" rasbora. There are a few species sold interchangeably with those retail names.
If the fish is acting normally, can eat, and the other fish do not develop symptoms I'd say to just keep an eye out and do what you've been doing. If the fish IS diseased, it's likely in your tank already so just be careful about not introducing new fish until you're comfortable that it is, in fact, just a malformity. A lot of fish come from breeders and wholesalers that should never have been raised to early adulthood for sale. JMO.
If the fish is acting normally, can eat, and the other fish do not develop symptoms I'd say to just keep an eye out and do what you've been doing. If the fish IS diseased, it's likely in your tank already so just be careful about not introducing new fish until you're comfortable that it is, in fact, just a malformity. A lot of fish come from breeders and wholesalers that should never have been raised to early adulthood for sale. JMO.