It can't be a shark, John. When this ecosphere was created, they didn't make any sharks.
We scan for biologicals very thoroughly at all ports of entry. You wouldn't be able to get a shark embryo past Customs.
And before you even think it, you can't evolve a shark from our fish stock, in six thousand years, let alone the six hundred years we've had oceans.
The only people dumb enough to get spooked by shark tales are the tourists.
Right. Because they're the ones getting eaten by the sharks.