Great question!
1. There are sharks in the bay (inmate Brett mentions them), but you can't see them.
2. We also have rats in the sewers (I think).
3. And then there are lots of flies at the streetlight in the park.
4. There must be fish in the lake in Alaska (the guy is fishing, after all)
5. TechPet Coporation specialises in artificial pets, and their best-selling pet is TechDog, your highly configurable best pal, no expensive food and no walks neccessary.!
So there. Millions of animals. Ha.