permanent gill damage from toxins?
i posted earlier about a very "lazy" male betta who was rescued from some pretty awful conditions. this fish has definitely been exposed to high levels of toxins, likely ammonia for a while, then the nitrites, then high concentrations of nitrates because the tank was not cycled and just pretty much left for weeks or a month at a time with no complete water changes, filter sometimes not running, etc.
i have noticed the poor fellow breathes rather heavily compared to my other healthy betta who came from a great fish store that kept them in small filtered tanks. the suspect fish, as mentioned, very lethargic. also, his gills seem to feather out of his covers a little bit more than most bettas, kind of like he is about to flare in his fighting stance. i am suspecting permanent gill damage. anyone know the signs of this? i have read so many conflicting bits of info out there and can't pinpoint it to anything definitive. he eats and does normal betta things, but is just extremely lethargic and rests more than any betta i have ever seen. he has been in optimal conditions for 2 weeks and 2 days now.
btw: i have ruled out columnaris. there's no lesions on the gills and he'd surely be dead by now.
20gal: dwarf flame gourami, 16 neon tetra, 8 ghost shrimp
5.5gal: 5 glolight tetra, 2 threestripe corydora
5.5gal: royal blue/purple butterfly rose tail betta
2.5gal hospital/QT: 4 neon tetra