Lone zebra danio, is dark with no stripes and top fin is clamped

[janegael]

Poor guy is the only long fin danio left with 7 pepper cories in a 20 long. The original school of danios was getting old, so two years ago I added three new fish. One by one the older ones passed and one of the newer ones as well. I got all them as adults, so I don't know how old they were. My last two danios looked bloated two weeks ago. This one got better but the other one had to be euthanized. I thought that his getting dark was part of the bloat but his colors aren't coming back. He eats well and is active in the tank, with no obvious signs of disease.

I'm afraid to get him any new buddies as he doesn't really look healthy but I have no idea what to do to help him. Also, would getting some cardinal tetras be okay. I'd really like to change the tank up and add a little color. I could move him to a heavily planted 29g with 5 cardinal tetras, 3 pearl gourami and a couple of panda cories.

 

[Naughts]

It has a bent spine and doesn't look well. I'd be reluctant to add any other fish in case it's infectious.
If you could get a clearer picture that may help people make suggestions to help the fish.

 

[Byron]

Given that issue, I would in kindness euthanize the fish. Then give the tank a few days while you consider options going forward.

I will just mention that if you intend keeping the cories, you really do need to change the gravel out for sand. Now is the time to do this, before you begin adding new fish.