There are several ways to do the aquaculture thing as well as several different fish and crayfish you can grow.

Basic system description-

Tank for the fish and a tank for the growing medium and plants. That is all there is to it. You pump the water from the fish tank into the second tank which is usually mounted higher than the fish tank. Once the water reaches a set height in the plant tank it will activate the siphon and drain back to the bottom tank. This allows the roots to get flooded with the nutrient rich water from the fish tank as well as filter the water for the fish. You can also grow things like lettuce in rafts on top of the fish tank. The rafts are nothing more than styrofoam with holes for the lettuce roots that float on top of the water and you harvest as needed.

It gets a lot more technical than this, but I didn't want to get too into it. I guess I could start a thread on it if there was enough interest.