Hi there,
Hoping to get a second opinion on my Espy's rasbora (aka porkchop rasbora), which seems to have developed a mysterious lesion/growth overnight. The lesion is at the base of the tail and appears as a white protrusion when viewed in profile. I would say it's growing internally and protruding through the scales. I've pulled the fish into a quarantine tank and am preparing to treat.
I had another individual in this school of fish manifest similar symptoms in November. In the previous episode, I quarantined the fish and treated with a few remedies (Maracyn 1 and 2, maybe Ich-X, aquarium salt), but the lesions grew and spread, and the fish succumbed after a few weeks (in a quarantine tub). I have some pictures of the more advanced disease from the previous case if that's useful.
The symptoms don't seem to match any of the usual suspects so I'm a bit at a loss as to what I'm dealing with and what might be effective. The only thing that seems to fit is mycobacteriosis, which 😬😬😬. I'm not terribly keen to trash the fish and plants and nuke everything with lysol, especially not across the multiple potentially cross-contaminated tanks – I do my best to keep things clean and separated, but I'm realistic about the limits in a home setting.
The sick fish was in a 40 Gallon breeder in a school of 8, along with a couple of cories, 5 otos, a bristlenose and 2 dwarf flag cichlids. All fish save the one rasbora look healthy and normal. The tank has been running for 6-8 months and has a pretty well established plant community. No fish have been added (or removed) since December. Water parameters have been stable for the duration of operation.
Temp 23-24˚C/74-76˚ F
GH ~180 ppm
KH ~80 ppm
pH 7.6-7.8
Ammonia 0
Nitrite 0
Nitrate ~20
No significant changes have occurred to the tank recently, save adding a new Anubias, which was bleach dipped and quarantined for a week.
Looking forward to outside input. Happy to provide additional information as required. Thank you.