Big white bump underneath betta fish’s neck!

Hi Everyone

I have a betta fish and have had him for about 6 month now. He has a 2 gallon tank, a heater, and a filter. He also has a bunch of plants and stuff in his tank. Today I was checking the tank and saw that he was sitting on the top. I looked closely and saw there was this big bump underneath it’s neck. I changed the water entirely when I came back from a vacation and she was completely fine then. It’s been two weeks since I came back and I see this on her. What could be causing this? Is this a tumor? Is this inevitably fatal? Please help. I’ve attached some photos.

Hello, and welcome to the forum!

It looks like dropsy to be, @Colin_T, is better at fish illnesses then me.

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Hi and welcome to the forum

Can you post a picture of the fish so it is in a normal position, not standing on his head.

It appears to be bloated, possibly from dropsy.

Is the fish still eating?
What does its poop look like?