Can I specify a public key file instead of recipient when encrypting with GPG

Can I specify a public key file instead of recipient when encrypting with GPG

1. Can I do something like:

   gpg --public-key my.pub  -e file.txt
   

2. If I can, any reason that I should not do that?

P/s: I think I don't need to know about the recipient because my machine only has one public key at a time.
But that key will change soon (and I can delete all the old encrypted files, so no need to keep them).