Legal question:Selling house with built in tank, are fish pets?

[TheMikey]

If the tank is a fixture, it sells with the house as it is deemed part of the house. Keep in mind, that's the empty tank, the actual property.

Contents of the tank are yours to do with what you please and, my guess is that the tank sells along with the house and it's the new owners issue.

Of course, all the internet advice in the world won't top a real estate lawyer and a brief consultation. Know your rights and position before you make a decision.