Transferred my 3yr old male koi betta to a 5 gal tank about 6 weeks ago. The tank was cycled, parameters are ideal, weekly water changes and tests. Filtered and heated tank. I noticed today a fairly large growth on his head that wasn't there yesterday. The fact it grew so quickly has me concerned. He's always been on the mellow side compared to my other bettas. He's been lethargic, not terribly interested in eating anything I give him. Judging by the photo does anyone know how I should move forward with treatment? I've never dealt with a tumor before, I know there's not much to do for them. But if it looks like an abscess or infection I can attempt treatment.
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