I have what I believe to be a male yellow-tailed guppy in a 20 gallon long. I have noticed what seems to be a pretty obvious crescent-shaped, what appears to be, bite mark in the top of his head behind his eye. Looking at him top-down, his head looks swollen, gray and rectangular (not the normal, slimmer, oval) guppy shaped head. The rest of his head is lumpy and some scales protrude outward from his head. The only other bigger fish I have in the tank that might be responsible are a wagtail platy and a lyretail Mollie and black Mollie. Should u medicate or remove the I'll fish ?