I've spoken to Loftar about this already and he's in favor of this type of thing which is nice. I've also spoken to Jorb who has told me that with the current fluid mechanics (or the lack of one) it means that we cannot easily have ponds implemented.
We currently have glass panes available to us. I propose that a few nails, 2 boards and 5 glass panes can make you one fish tank. These can be lifted when empty and crafted indoors or in mines. You add water/coarse salt (depending on the fish type) and then right click the fish you've caught into the tank. The fish then floats around inside with a graphic based on the type of fish inside (pls not one generic fish). You are able to crush up seeds and feed these fish as you would turkeys or other domesticated animals and as they breed, they increase in purity. This will add a usefulness to fishing itself, add a new industry and will give players new design options for their living spaces.
Another thing about these is that if there are ever other additions (such as lizards in badlands) you could add dirt instead of water to have a home to breed those also
Some bonuses to this:
If you keep snakes you could potentially harvest their venom (poison blades, poison for witchcraft etc)
Frogs for frogs legs/decoration/potential bug catchers
Crabs for their meat/decoration