I have several fish called Chromises in my aquarium. The photo above looks quite dull, but they are very colourful blue-green fish that like to school. A school of chromises looks quite fantastic.

While I was feeding the fish on Saturday, one of these guys swam rapidly to the surface (they do feeding frenzy really well) then shot to the bottom of the tank, hitting a piece of rock on the way. Then it lay flat on the sand at the bottom, not moving for some time.

I always expect the worst, and I thought the impact must have killed it. However, an hour or so later, the fish was missing from its previous resting place and was happily swimming around.

What was weird was that there was now something like a clear plastic ring around its mouth. You could see that it was able to open and close its mouth OK, but there was this strange thing right on the front of its face. Had it picked up some plastic refuse from my tank?

The next morning the fish was back to normal appearance. I think that it must have given itself the fishy equivalent of a fat lip in its strange accident.

A few days later and it is still right as rain. The incident is something of a mystery.