I don't think that tank would hold all of them for two more years.
You could try selling them now and restocking it with fish that will be able to live the entirety of their lives in that tank.
Hmm ok.. so really we only can get the "stock" small pets, nothing exciting.
The thing is, some small rodent pets that I've seen for sale in the US can only survive in dry, arid areas i.e. not NZ. So if they don't pose a huge threat to our native fauna, why can't we get them here?