Sourcing your fish
The first decision you have to make is what fish to grow. This depends on whether you intend to eat them or just keep them for pleasure. While the principle of aquaponics is primarily to grow food, it may be that you prefer to grow ornamental fish such as Koi Carp or Goldfish and just eat the plant produce. If this is the case you are likely to use lower fish densities (hence feed less) and therefore the amount of plants it is possible to grow will be reduced.
If you are planning to eat your fish, there are a number of species to choose from such as carp (common or mirror) and perch to name just a couple, but the one we strongly recommend, certainly if you are new to fish-keeping and/or aquaponics is Nile Tilapia (Oreochromis niloticus). It is a tasty fish, that is hardy and tolerant, which can be kept at a high density and is resistant to disease. With the right conditions they can easily be grown to harvest size in six months.
Fish should always be sourced from a reliable and reputable supplier, if in doubt, ask to see any paper work related to where the fish stock came from. Generally speaking, fish that have been bought for ornamental purposes should not be eaten as they may have been treated with harmful additives. When buying fish that are held in a tank avoid those that are being kept with sick fish or those that look stressed. When transporting your fish back to your fish plant system, try to keep stress to an absolute minimum.
Information below is reproduced with kind permission of Aquaponics UK.