There are 5 different development stages for your Fish.

To develop him, you must give as much attention as he needs. You´ll have always to persist in the weakest characteristics to pass to the next stage. For example if he´s hungry, you´ll have to give him food, if he´s unhealthy you´ll have to give him health care.

However, your Fish´s experience is the most important attribute. When your Fish reaches the next level, his experience resets to zero. So you must gain all the experience you need to achieve the next level.

Reaching the highest stages of development is always more difficult so, you need to be more dedicated. Every time your Fish develop you have more chances of getting better and rarest items increasing his attack and defence power. Moreover you can’t forget his time, because they must have a certain age to reach the next development stage.