Lump, Pimple, Wart on Oscar Fish Lower Lip
It is fairly common for your Oscar fish to develop a strange lump or protrusion on its lower jaw. These lumps are often described as looking like pimples, warts or even zits coming to a head. As far as I'm aware this lump hasn't got a scientific name, although I did see the word "chinple" appear somewhere.
I can't honestly tell you why these lumps appear. However, they do often appear when the Oscar is approaching maturity. As anyone who has Oscar Fish will tell you, Oscars absolutely love to dig around in the substrate as well as vigourously cleaning the flat rock which they often monopolise as their own. Because the surface area needs to be clean, they use their mouths to scrape any dirt or debris off the rock. I believe that this pimple develops because of this reason. I have no scientific proof to back up my claims but many of the Oscars I have had over the years have developed this protrusion in the exact position on their jaw that they use to clean their rock.
It may be a possibility that the pimple looks sore and may even grow in size considerably. However, unless things look as if they are getting infected you are probably best leaving things alone. These pimples are obviously a common occurrence with Oscars so I don't suppose there is much we can do to stop them happening. It's probably a case that they have some kind of purpose, but like I've already said I couldn't say exactly for sure why Oscars do have these strange protrusions on their lower lip, it just adds to their attraction at the end of the day.