Instructions
Add friends to your "Happy Aquarium" game by clicking on "Send Invites" and typing the name of your friends into the field. Hit "Send" when you have added the people who are going to help you get a platypus.
Play the game as normal and wait for an adoption invitation for a platypus. Adoption invitations occur randomly during the game for all players.
Tell your friends to send their invitations to you when they receive them. Watch your Facebook news feed wall to catch when an invitation occurs.
Click on the invitation on your wall and select "Accept" to adopt the male platypus. The male platypus will now be in your aquarium.
Repay your friend's favor by doing the same thing for them when you get an adoption notice from the game.