betta help

[m33p]

Hi! Can anyone please help with telling me if this is a fungal infection or HITH or something else? I’m not sure what it could be and I want to treat it accordingly. I noticed a small patch on his head and the next day this is what it looked like. He is starting to swim around less but he is eating.

 

[Uberhoust]

That is a large amount of damage to the poor fish. I don't know fish diseases well but if he were mine, I would euthanize him. Others who know more about diseases, might offer another suggestion.