Those fish must have taken a battering
On the other hand, this feels especially sad for some reason.
To be fair, you have to catch and release most fish in the UK which, whilst annoying for the fish, doesn't seem to do them much harm since there's e.g. a whole bunch of 30y+ old carp that keep getting caught.
You're allowed to keep a certain set of game and sea fish if they're big enough and from the appropriate place.
Warehouse cats can be nice warehouse companions too (depending on what happens in the unit).
I've had to do some mouse removal work in my forest adjacent home, and it's not pleasant, but neither is having mice around.
In Costco they sell this cat food called ‘Maintenance cat’. Maybe we need one of those cats.
Of course, cats can cause a different sort of trouble than mice. :D
If your friend had 30 tanks and thousands of fish, they should have had a more involved backup plan that involved a dedicated generator in addition to a UPS. A small generator would have been a tiny fraction of the materials and livestock costs of running a setup like that.
Though the moment the UPSs hit 50% you might try to run to Home Depot and grab a generator, but by that time they'd all be sold out.
Agreed though that it was a ticking time bomb. As for better backup plans: even autostart generators for data centers can fail when you need them most. Backup plans end up with more and more layers until you think you've got it all and then some little oversight will get you. In his case he probably could have done more but that's only because we're looking at it after the failure, for decades it worked.