Help with Platy

[JL1010]

Hi everyone, first time posting here and just looking for advice. Does this look like Dropsy in our Platy fish? And if you think it is, is there any advice on what we should do? Our tank is an established tank (about 3 year old). No new fish added for over a year and no sudden fish deaths. I am by no means an expert but we have never had any issues in our tank. I check water ammonia, nitrates etc all the time and they are all fine. All other fish are fine.
Fish in question is behaving as normal and her scales haven't protruded.
Thanks so so much in advance. Just want to do the best for the fish. We've had lots of Platy fry in the past but I don't think she is pregnant. Not 100% though.

 

[Colin_T]

How long has it been fat like that?
Did it get fat suddenly or over a period of time?
Has that particular fish ever had babies?

 

[JL1010]

How long has it been fat like that?
Did it get fat suddenly or over a period of time?
Has that particular fish ever had babies?

Hi! Thank you for your reply. It seemed to happen relatively quickly over a few days and she has been like that for about 4 days now. But hasn't become lethargic and is still eating and is still as active as all of the other Platys.
I'm not honestly sure if she has been pregnant before as we have 5 females in the tank. I don't ever purposefully breed them. Just often wake up to a few little fry in the tank.

 

[Colin_T]

How fat was it last week before it gained the weight?
What does its poop look like?

 

[JL1010]

Not fat at all. Quite a slim fish and standard Platy. She hasn't actually pooped for a while that I've noticed come to think of it. Unless she did during the night.

 

[Colin_T]

Tumours normally grow slowly so this is unlikely to be a tumour.
Cysts can grow rapidly but not normally that much that fast.
If the fish is still eating well then it's unlikely to be an internal bacterial infection.
Developing babies don't cause them to get that big that quickly.

Don't know, it could be a combination of an internal infection and a cyst.
There's unlikely to be a cure because most internal problems are hard to treat.

Monitor its poop and see how it goes, but my guess is it won't end well.