I have had my fighter for over a year and a half now and otherwise he seems perfectly healthy (swimming around, no clamped fins, eating normally). A few months ago I noticed a slight pale discoloration right at the front of his dorsal fin, where it attaches to his body. Since then it has slowly grown into as round, white lump about 3-4mm big. Last week I could see some red veins (or what I thought were veins), but since then he has scraped some of the white flesh off and it's quite red underneath. There is a post on here from 2011 that sounds exactly the same, but it wasn't answered. He lives in a 20L tank with fake and real plants, water changed every week, Indian almond leaf added, all parameters perfect when checked two weeks ago. Salt added at 1tsp per 4 litres. Eating hikari pellets and another brand I can't remember, plus some frozen community food every now and then. It's probably just a tumour, but if anyone has an idea I'd appreciate to know for sure.