Is this mouth fungus? Goldfish

Hey guys.

One of my goldfish developed some kind of sore on his mouth like 4 days ago. Ever since then it has become elevated and has some white growth on it.

All my fish were just moved to their new 125 gallon tank 2 nights ago. I really don't want to catch the fish to treat him. Not only is it gonna be hard in such large tank but fish act frightened and swim jerky when I am around cause of the recent handling.
What do I do?
They are still stressed from transfer and won't eat.

Do I just leave it as such? I think if left untreated it is gonna get worse? What is the best course of action?

Please help! What to do?

Water parameters are 0, 0, 5 (newly cycled tank). No other fish show signs of this.

 

Can you take a macro photo of the growth? I want to be sure.

 

Can you take a macro photo of the growth? I want to be sure.

Macro photo? Do you mean a better close up? I think that was as close as I was able to take.
I can try again tomorrow, as I am away now.

Thank you Andrej for trying to help! *hugs*

 

My theory is that it is lymphocystis. Goldfish often have it on their mouth. Is it growing?

 

My theory is that it is lymphocystis. Goldfish often have it on their mouth. Is it growing?

Oh I did not even consider that. It started looking as a cut on his lip. It was red and had some black dot in the middle. Then the white stuff started growing
I also seen him isolate by himself away from other fish but could be coincidence.
Yes, it seems to be getting bigger When it first appeared it was looking like a cut. As days go by, it is getting bigger in size.

I really don't wanna stress all fish with catching them. They all used to handfeed. Now they are terrified of me

 

I was able to take a video of the spot on his mouth. Poor fish. Today it kinda looks like barbels or mustache. Is that growing fungus?

This fish was also seen shimmying as if vibrating in place. No other fish ever did it.

Appreciate anybody's advice and insight