When choosing a type of fish for your aquaponic system, there are three things you should consider: climate, consumption, and weight.
Most examples of aquaponics will use tilapia. But that’s only because aquaponics, as we know it today, started in tropical places where tilapia are common. Tilapia have a lot of up sides in warm weather climates (they are hardy, edible, and grow really fast); however, it is not advisable to try and grow them in cold weather climates because they like 75°F water and that’s hard to maintain outside. Instead cold water fish like perch or koi would be a better choice in the north.
The other thing to decide is whether you want to eat the fish or have ornamental fish. Edible fish are a great option because you will not only have plants to eat, but healthy fish too. Beware: You may get too attached to your fish to eat them. Of course, selling koi can also be a lucrative option.
Finally, the ratio of fish to water is 1 pound : 10 gallons. So if you have a 200 gallon fish tank, you can grow up to 20 lbs of fish. Remember to consider how fast they grow and how big they get when buying your fingerlings.