how does the council know you have a dog?

I just brought a dog and have transferred ownership on Central Animal Records. Does the council get notified that I have a dog at my address?

I don’t want to register my dog yet as I’m waiting for him to be at the age suitable for desexing (he’s 4 months) so I can pay the reduced rate.

Has anyone kept a pet without registration with the council? How does the council know if you don’t register?