Disppearing minnow

I lost a Zebra Danio during the cycling of my tank. He just stopped eating after a water change and then died about three days later. Your fish could have internal parasites (not much hope, there) or have a bacterial infection. I hope your fish recovers. Does it stay in one place and just swim side-to-side? And have clammped fish? It could be the 'shimmies'. I'd suggest putting 'Stress Coat' or something similiar in the water. It may be too late for that fish, but the others will benefit.

I had quite a similar experience with a Zebra Danio in one of my tanks that I just finished cycling. He just chilled by the filter intake and swam sluggishly against the current for a couple days and then swam under a airstone to die. Quite similar signs to what yours experienced, but I wasn't sure if it was nitrite poisoning or maybe he came down with a intestinal parasite due to a supressed immune system. He ate his last "supper" one evening and then seemed to be doing better, swimming around and whatnot. The next morning he was dead..... Did you notice anything odd about his doo-doo? I know if they have intestine problems sometimes mucous accompanies the excreta and it gets white and stringy....nasty. Just an idea.... Good luck.

steve