Fish are an important part of any aquaponics system since they provide a lot of the raw materials that will be later converted into nutrients for your plants and vegetables. There are two major groups that we can separate the fish into. One group are your ornamental or “pet” fish. These fish are raised solely for their visual appeal and will not be harvested for food. The second group will be raised for food and in some cases even used in feed for other animals. It is important to decide early on whether you will be harvesting your fish for food since there are a few things you can do to your system to optimize them for each group. It is important to consider what environment the fish you choose to raise will thrive in. Some fish do well in dense stocking tanks where others do not do as well. There is also a consideration as far as water temperature to consider. Remember that you will be growing three crops in your system and they all have to be happy in order to get the most out of your system. In a complete closed loop system you will have your fish, beneficial bacteria, and plants. Each of these three have their optimal temperature meaning a temperature that they will produce the most for you.