I lost two of my 5+ year old denisons to some sort of mouth problem.Not a fungus ,possibly bacterial ,but real issue was mouth would not function well enough to keep fish healthy over months.
I treated the tank with prazi and then metro .Neither seemed to do anything.
I could have treated with kanna and furan2 but just did not see an issue in the tank.Just the two roselines ?
For what it is worth almost all Denisons are bred and raised on our favorite Asian fish farms behind the curtains [read on breeding Denisons].It is all induced and achieved with steroids so IMO
I just hope they haven't turned this fish into another dwarf gourami !
They are one of my all time favorites and I am 99% certain when my school drops below 6 I will get another 6-7 to add. Mine are over 6 years now ,the remaining 7.
Cool fast water for them and keeping it clean is best.
I have found in other tanks that a prophylactic dose of methylene blue never hurts ,and often helps.