I have a little guppy that's been hanging out on the bottom of the tank for a few days. He's been avoiding light and trying not to swim a lot. Generally lethargic. He's the same age as the other 3 in the tank and they're all quite happy and eating heaps where as he has a few little bursts of interest then goes back to hiding. He's a lot thinner than the other 3 and his gills seem to be working overtime. He doesn't seem to swim with his tail unless he really has to and I thought I saw him swimming with his gills at one point but surely that can't have been right. This evening he was floating vertically with his head up in about the middle of the tank so I figured it was time to see what I could do.

I've moved him into another tank, which luckily I set up earlier today to try to cycle (hopefully he makes it and it cycles with him), and I've followed the salt treatment plan on the guppy ailments website. Should I do anything else? He doesn't seem broken or have any ulcers but his tail looks a bit more raged than the others and the lack of action is concerning.

I'm new to this so i'm reading everything on the net and probably over-reacting.

Turns out he's paralised - swimming with his pectoral fins only. Euthanise or let him keep going?

The thin-ness I particularly don't like the sound of. There is a guppy parasite that causes all sorts of problems, one of which being that they waste away – good thinking for moving him quickly to another tank. My feeling would be that given all his other symptoms it's not looking good for the wee fella and it might be best to euthanise him if he doesn't look like he's improving.

So it looks like he's on the mend - but the rest of my guppies have come down with it to some degree (not as bad though) so they're all in the med tank for the next couple of weeks. The salt treatment works wonders and he's put on a lot of weight in the last few days which is great. He's also swimming with his tail again after one massive bowel movement, I assume that was causing the paralysis.

Spoke too soon. Seems he got too cold last night when a heater failed and he died while I was trying to net him to move into a warm tank. Clearly just got too stressed. Damn it, he was looking so much better and was completely back to his old self.

Oh dear, sorry to hear that!