Where did these fish disappear to?

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Bob Mehen gives his advice to a reader who is concerned about why his Cherry barbs are disappearing.

Q) I recently set up a 40 l temperate aquarium with live plants. I added three danios, followed by six Cherry barbs a few weeks later. I also bought a hillstream loach several weeks after that. They all seem very happy and I am carrying out frequent water changes.

However, one of the male Cherry barbs completely disappeared about a week ago. Now a female Cherry barb has completely disappeared overnight. I cannot find either of them anywhere and I’m baffled. The holes in the filter are not big enough for them to accidentally swim in there. Do you have any ideas please?

DENISE EDWARDS, VIA EMAIL

A) BOB MEHEN REPLIES: Disappearing fish is one of those mysteries of the hobby that all fishkeepers will have experienced at some point, and it’s always frustrating when you can’t find out what happened to them. One thing that time will show is that fish are amazing escapologists and if there is a way for them to get out of your tank, then sooner or later they’ll probably find it — often with fatal consequences. The first place I would check is behind and underneath your tank where unlucky adventurers usually end up, dusty, dried up and, sadly, dead. While you don’t want to seal up your tank completely, check the hood and any cover-glasses for gaps where fish might be able to get out, and block them up if possible. Dropping the water level slightly can help as well, but you’ll need to be careful as your tank is a small one and every litre is precious with regards to stocking. If the tank is open topped it’s worth considering adding some floating plants which can help fish feel more secure and prevent them jumping.

It’s also possible that the two fish have simply died and been eaten by their tankmates. Gruesome though this sounds, fish are very efficient at ‘tidying up’ and most won’t turn their nose up at the chance of some free protein...