Fish rescue around Clapham, anyone?

My wife's office has a large goldfish in a tank that looks set to be abandoned – no one there can or will take it. I'm not yet sure of the size of either fish or tank (still waiting to find out), but I think it's more of a large tabletop set-up rather than the wall of a building...

Worst case is that I'll collect it and figure out how to look after it in a house with two cats, rather than leave it to starve, but I'd rather try to get someone who knows what they're doing to take it on (and ideally, not eat it other than as an absolute last resort...).

So can anyone here help? The office is on Clapham high street, so I'd rather someone local took it to minimise transport across London – I can get it to you by car (though I've no idea how to transport a fish – suggestions welcome).

Seatbelts, obviously.

Can you not just get one of those massive feeding blocks you chuck in when you go on holiday for two weeks?

https://www.aquariumkingdom.com.au/tetra-vacation-14-day-fish-feeder-block

Yep, it has one of those, but no one wants to be responsible for replenishing it or cleaning the tank. There are obviously more pressing things to worry about, but the thought of abandoning a living thing to swim around in its own shitty water before starving concerns me. I'll take it as a last resort, but I have two cats, so it's not ideal.

Most aquarium fish are fine only being fed once every week or two for a while. Lowers the tank maintenance requirements too.

Goldfish in particular tend to thrive on weekly feeds in properly established tanks.

Funnily enough i used to work in a fish warehouse when I was a schoolboy.

If I were you just go over there , clean the filter out using the existing water, rake the gravel up a bit and get any shit out that you can , do a partial water change (10/20pc is fine but make sure the water isn't too cold) then lob one of those feeder things in and you should be ok for a while, as long as you keep doing the partial water changes every 14 days.

Moving the fish should be an absolute last resort.

It's a kind thing you are doing.

Solid advice. They're hardier creatures than many realise.

Fish breeding used to be one of my many weird hobbies.

Just tap water? Does it need treating in any way first? I know nothing about fish... I'm led to believe the tank is filthy and has no gravel.

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Sorry, read Clapton..

Always mix those two up.

It's good practice to use a tap safe additive product but a few weeks without using it is unlikely to harm the fish. It's more important it has relatively clean and unpolluted water at the right temperature and some grub to eat.

To that end if the tank is near a window then lower the blind a bit which will shade the tank and hopefully marginally improve the water quality and pollutants in the tank.

You should also punch whoever was responsible for getting it in the office and who then decided it wasn't their responsibility

It's good practice to use a tap safe additive product but a few weeks without using it is unlikely to harm the fish. It's more important it has relatively clean and unpolluted water at the right temperature and some grub to eat.

To that end if the tank is near a window then lower the blind a bit which will shade the tank and hopefully marginally improve the water quality and pollutants in the tank.

Great, thanks. Will do, then I'll take it from there.

You should also punch whoever was responsible for getting it in the office and who then decided it wasn't their responsibility

Tell me about it...

Aquatic shops will usually rehome fish like this

If its still there and visible from the street, and Clapham Waitrose remains gutted, I guess it will transported into some local batter and laid to rest with a lemon and some poncy chips within a week.