A new feature released 08/15/2011, give you an exclusive bonus fish for collecting other fish in a set.
Click on the purple “Collector Sets” button that now appears at the bottom of your tanks. A new page will open. This page will tell you which fish you need to collect in order to complete your set. You may already have some!
You must collect EVERY FISH on this one page in order to claim the prize.
Click on the “i” next to each set and you will see a pop up window explaining where each fish can be found. Find the fish/decorations by going to the store and buying them, trading for them, or asking your friends to help.
You can ask your friends for help by clicking on the symbol next to each fish and posting the pop up to your wall.
Once you have collected all items on the page, you will be allowed to claim your exclusive fish by clicking on the “Claim” button that appears under the exclusive fish in the top left hand corner of the Collector Sets window..