I bought a few Neon tetras yesterday, been keeping them in a ~10G quarantine tank, and I noticed one of them lying on the bottom of the tank. At first I thought he was dead, but I noticed some twitching movements, so I took him out of the tank and have been keeping him in a small jar, so I can monitor him more closely. You can see two pictures here (with different backgrounds for better contrast). To be honest, I suspect there's not a lot to be done (although I'm hesitant to euthanize him), but can anyone point to what's wrong with him, and whether I should take any actions to stop the others from following suit? Thanks in advance!