Wealthy fish fanciers often display their hobby via aquariums integrated into the walls of their home. If you find that idea intriguing but a little dull, may I suggest the integrated doggy cage? It makes for a striking feature in any library or study and a great conversation piece when you have guests over. Animals to put inside it might be a little hard to source than your average guppy, but you can always adopt from your local dungeon.
The cage here is available for rent as part of the BDSM loft in Berlin. However, I’m not sure who the domme is. If you can help with that attribution, then please let me know via a comment.
Alternatively, stick with the aquarium idea but expand your concept of pet play to include human fish, as the magnificent ladies of the OWK did (many) years ago after they found one of the poor things beached by their private lake: https://contemplatingthedivine.com/wp-content/uploads/2011/02/OWKFish_montage.jpg
Best wishes
S