I've noticed a difference in my platy and since im new to this type of fish and never seen a pregnant fish before I was curious if my fish could be pregnant. I added some current pictures and also one of what it looked like when I got it.
Your platy seems to be a male judging by the gonopodium, so pregnancy is out of the picture to me. It could be the result of overfeeding or possible swim bladder issues. I'd monitor him to make sure that there aren't behavioral changes. Beautiful platy, by the way! I can never keep them alive...
Thank you and I figured that as well looking at the fins it just seemed to grow much larger than the other in comparison. I will definitely be keeping a eye on it a little closer