Fish TB? or just bad luck

[Kaijuaquatics]

Ok so I'm going to get really in detail with this to compensate for the fact I don't have any pictures of the guoramis when they were sick so bear with me.

As a bit of backstory, I used to be into keeping bettas. I had 2 in a row that died of dropsy and one who's death is still a mystery as I don't know what caused it. All of these fish were housed in the same tank (roughly just over 10 gal) at different points in time, but there's always been the same small group of harlequin rasboras that are present to this day. I've lost some over time so I'm down to 3 from 5, but as far as I can tell neither of the 2 casualties had any symptoms concurrent with TB.

In case you want to see the mystery death betta, I have a picture of her the day she died:

As you can tell, she was in pretty bad shape (she used to be almost pure black) but I couldn't definitively identify what was making her sick.

The other 2 bettas lasted quite a substantial time (6 months onward) before they died of dropsy. Recently I've been told that mycobacteria is the main cause of dropsy in bettas, and I'm worried that was the cause of all their deaths.

Onto present day, a few months back my bf bought me two red Robin guoramis for the tank. They came to me perfectly healthy and were ok for a while before I noticed them deteriorating. One barely moved from the same spot and both almost looked stunted, like they were suffering from malnutrition. The red colouration was also slowly fading and they were almost white on the bottom half of their bodies. Both have now sadly passed.

Do you think that this is TB? For context this tank has been set up several years and gets a 40% water change every week. The bristlenose pleco and harlequin rasboras are perfectly fine and active. Heres a picture of it if you're interested:

 

[Colin_T]

I doubt TB is the issue if the rasboras are fine. They should be dying from it too if it's in the tank.

Gouramis and Bettas can carry the gourami Iridovirus that can kill and it remans in the tank after the fish have gone.

Malnutrition, worms, gill flukes, poor water quality, inbreeding and other diseases (besides TB) can all be a contributing factor.

The most common sign of fish TB is the fish stop eating and swell up over night, do a stringy white poop, gasp at the surface or near a filter outlet, and die within 24-48 hours of showing these symptoms.

Fish TB (Mycobatceria species) damages internal organs causing organ failure. This causes rapid bloating and the fish dies in pain due to internal bleeding and damaged organs. There's no cure for fish TB.

You could try getting gouramis from another shop or supplier, or getting normal fish instead of colour forms and weird mutations. They might do better. If you continue to lose gouramis and Bettas, then try a new tank and gear and see if they still die. If they do, then it's probably the fish and supplier.