It looks lke an injury to me too. Have you got more gouramis? Fighting can result in mouth injuries.
I would keep on top of water changes, maybe increase the size and/or frequency of them. That helps anything to heal, and reduces the chance of an injury becoming infected. It will probaby heal, but keep an eye on it, to see if it gets worse or becomes infected, for instance with fungus in which case you will need to treat it.
If there is any fighting going on, you could provide more hiding places where the fish can keep out of each other's way when they need to.
btw. that's a Dwarf Gourami, not a Blue Gourami.
Thanks for that. I too do think it’s more likely to be an injury as it appeared fairly quickly. As for water changes in general I do 50% per week but have increased the frequency to twice a week currently due to the introduction of tannin-leaching bogwood. I have 3 Dwarf Gouramis that in general are very placid and not seen a lot of squabbling, but that doesn’t mean they won’t ever fight. I will monitor the ‘injury’ and get in some medication ready JIC