Throughout the game, you will be able to expand the pond by catching certain fish, and crafting gems. Each time you complete that level’s challenges for catching prey, you will be able to go to the portal, and the pond will expand.
There are 8 portals to open. You can see the progress on the “Path to ascention” on the Koi Details screen. It looks something like this:
So for the example above, this Koi only has one more portal to open before it can ascend to become a dragon.
The challenges to complete for each portal get more and more difficult, but usually by the time you’re approaching the last few portals, your Koi stats will be pretty high, so catching prey will be pretty easy.
Once you’ve completed the last of the prey, craft the gems to open the last portal and enjoy the ascension sequence!
When you ascend, you receive a pearl, that you can spend on different items in the game, like cloning Koi, and you also receive a Dragon Point. Dragon Points are kinda like a high score, but you only achieve them when you ascend, so it’s likely you won’t be getting hundereds of points without spending hundreds of hours playing.