Holiday Disaster

But not at all the kind I'd envisaged.

We are just back from two weeks away, and it left my mum in charge of the fish, with lots of specific instructions.  I was still worried though, and I did think I may well come back to all my fish being dead.

It's a new tank, so it only has 6 harlequins in it.  Last I spoke to my mum, she said there were only 5.  Then 6.  Then 5 again.  But they do zip about, so I thought she's probably not counting right.

I get home, and there are only 5. Definitely. 
So I call my mum and ask if she's removed the dead one. 
Apparently not, because she couldn't find it.  So I have a search.  I can't find it either.  Very strange.  My mum decides the others have eaten it.  I think not, but it's easier to just agree.   

Then hubby comes in, and finds a dead fish on the sideboard.
So I have NO idea how that happened.  The lid of the tank has two small holes, but the fish is at the other side to that, so unless it got out of a hole and then walked round, that's not what happened!  The only other thing I can think of is that it managed to leap out when my mum was changing the water (only about 2-3 litres with a jug) and she didn't notice.

I suppose the good news is that all the others are OK, but I'm still sad about my sixth zippy little fish (and bemused).  I'll have to get another couple now to keep the 'shoal' complete.

Can they get out of those small holes in the lid? 

The lid of the tank has two semi circle cut outs so you can lift it on and off.  The water is about 1.5cm below that (can't go lower because there's a minimum fill line, I presume for the filter)

But if they can get out of that, should I cover it in some way?  But wouldn't that affect air flow?