By feeding and taking care of your fish everyday in "Sakana to Asobou! Aqua Zone DS Kaisuigyo", you'll be able to earn points. These points increase the range and number of fish you can keep as well as unlock items to put inside your tank. Occasionally bottles with messages in them will also appear inside the tank giving you "special tasks" to complete, allowing you to earn larger number of points.
As time goes by your friendship level with the fishes will change too. With a good friendship level, you'll be able to use various actions to communicate with the fish such as tapping the screen to make them gather together. There are also mini games such as guiding your fish through bubbles.
Due sometime in December from Gungho Online Entertainment. Ragnarok Online DS shouldn't be too far off then!
- Gungho Homepage