Its covered by your home owners policy under the property provision. If your policy covers 60k in property, and you have 60k in property plus 2k in aqaurium stuff, well you going to get stiffed on the aquarium part.
It not uncommon for insurance companies to give you what is considered depreciated value or used market value on items like TVs, stands, couches, etc...
So you may have purchased something for 2k, but its say 3 years old, and voila... the depreciated value is 1100. I think the only thing that is based on full replacement is the house.
I dont believe that live stock is covered unless you have a special provision in your insurance contract.