Fat Whiptail, Eggs Or Tapeworm

The first thing to check is the scales. I don't know much about whiptails, though. Do they have scales like 'ordinary' fish? If they do, are the scales lying flat against the body or are they sticking out? You'll be able to tell better if you look down on the fish from above.

I have not heard of tapeworms affecting fish, though I have has (or my fish have had) camallanus worms which are round worms. My fish didn't get fat, they had red threads protruding fro the anus when the fish hovered in the water - they go back inside when the fish is swimming. Do you see anything like that?

For now, keep a look out for it.

If you see it, try to look at its scales. If they are sticking out, that's dropsy which is caused by kidney failure. There are several diseases which can be the underlying cause but even if we could identify which one, by the time the scales stick out the fish is normally too far gone to recover.

If you do see red threads looking like the bristles on an artists paintbrush only red, you'll know it's camallanus worms. If this is in your tank, more than one fish will have them so look at all the fish.

if it's neither of those, I don't know what it could be.

Just spotted another whippy and it seemed fat as well... The other fish seem fine except one rummynose but I think that one has eggs, like the cardinals in the 190

  thanks for that @Littlefish  that's probably the only suitable explanation. And who knew buses now have wifi