Male guppy with bubble on fin

[Jessica Tomzick]

I got a couple of new male guppies today. Well my husband did. After putting them in the tank I realized one has this bubble on his tail fin. I was hoping someone could tell me what it is. I'm afraid it might be sick and I dont want it to get my other fish sick too. I attached some pictures. It's hard to see but it's a small orange bubble. It's the black and orange fish