Other variations

Of course there is, they can’t see the time.

As someone who dabbles in custom aquariums, this is actually a really cool concept that would be perfectly maintainable. You would have to take the top down to clean the tank, but I'm sure there's a clever hatch somewhere to feed them and you can keep all your fish food and supplies in the bottom drawer. You'd want to rubberize and seal the bottom of the top piece well (I'd probably just paint it with Pond Armor and put a rubber gasket around the edges). It looks like there's two pillars in the back to support the weight, so I assume there's a bit of a shelf or something. That's good design (the glass isn't supporting the weight of the clock on top). Also, it looks like the pillars are actually inside the tank with the fish, which is also doable (I assume they aren't real wood).

The biggest issue would likely be humidity causing potential mold growth inside the clock mechanism. I'd have to think about creative ways to mitigate that.

Yeah, just the sound of the incessant ticking drives me insane. I can’t imagine feeling it in my bones.

The fish tank's front panel can swing out, releasing all the fish and water

Humidity and fish access is probably the reason btw. Still looks awesome!