there are zoos without aquariums and aquariums without zoos, anyhow...
Eels, fascinating creatures. They can travel across land from one water source to another. Just think about that, its got no legs, its got no lungs and has gills and can manage that! Then they live for over 100 years some species, this is proven with something to do with age rings in otolith bones in the eels head (I don't regurgitate google info here) research this yourself.
Fish are probably my personal fav and what I am most knowledgeable (still very little!) about in UK and European freshwater sp. The downside for all eel sp. is that they are not interesting enough for zoos, 99.5% of visitors would walk by or pull a face near an eel tank, plus eels generally like dark conditions and to hide away or be wedged into something, then they are absolutely useless captive breeders compared to many other fish. Put all this together and you have a rather useless aquarium animal for the general public and aquarium owner. Remember the owner owns the aquarium to make money and not as a hobby to please weirdos like me and a few others who like eels.
Irrespective, eels are super