Oscar Fasting With Other Fish

So I have a maybe 3.5-4 inch oscar in a 75 with a bunch of other fish, there will be changes coming but for now everyone's happy. The one thing is, he seems to have some kind of a lump near his vent and I want to fast him for a few days to see if it goes away.
Pic (not mine but identical situation)


My question is, I want to fast him but I don't want to fast the other fish. Is there any way to keep him from eating? I know it's kind of a dumb question (he ate an ENTIRE cube of bloodworms tonight and now is sulking behind a rock because he realized how dumb that was) but I wanted to try.
Photo from littlemissdiva9.

 

The pictured Oscar is suffering from a "Prolapsed Vent".
Usually caused by severe constipation or an egg backup.
Feed a plant based flake food. Omega One makes several varieties.

 

Will it heal? I'll try the plant food but if there's meat in the area he'll go for it. It looked like it had gone down slightly earlier but then he ate all those bloodworms like an idiot.

 

The thing is though that there's nothing coming out, it's just the lump. Is that still a prolapse? Much confusion.

 

Epsom salt baths are a treatment option for constipation & prolapse. I have no experience using Epsom salt, but there is plenty of info on line.

 

Today it's almost gone, so I think I'm just going to wait it out. It's just a little bulge now. He's been doing fine this whole time, so hopefully it'll be gone by tonight. I won't feed them today and it should go away.

 

And it's gone! Thanks for the advice. He ate a few pellets just now and pooped so I think we're good.