I sometimes get asked some questions enough times that I wanted to try and answer here. I hope that if you use Marbled Crayfish in aquaponics systems in Texas (or elsewhere in the USA) that you will share your tips here with us as well.
An overview of a tiny 10 gallon system over 2 summers is at www.AquaponicsTexas.com, which has info and pics of one experience with an especially small system.
However I can share with you some tips for general comparison of other systems. As you know from your GOOGLE and BING research on aquaponics, there is a whole world of designs for aquaponics systems. Sizes, dimensions, all the elements within each system can be different. Given that as a premise, we assume that the outcome is a tank of tilapia, bass or catfish, feeding the crops of plants in a circulating system.
No matter the scale of an aquaponics system, I find it most helpful to have a separated tank to start a “colony” of marbled crays in. The reasons for this are:
1) Any tank populated with fishes of any size runs a very large risk that a crayfish will be eaten, usually before it even reaches the bottom of the tank. If it reaches the bottom in time to hide, it runs the risk of being eaten any time it tries to feed. However, I have seen cases where the careful placement of hiding places does allow a marbled cray to hide and breed in. The babies then become targets and there will usually be some survivors to learn to live in such a hostile environment. A tank devoted only to a cray colony guarantees an ongoing food supply.
2) A dedicated tank for the crayfish will generate a very high level of plant food. Whether it is included in a fully integrated system of water flow between multiple tanks and multiple plants, or a simpler flow direct between the cray tank and plants, you will have some serious plant food coming from the cray tank.
Another thing that seems to benefit both a cray colony tank and a tank with fishes, is a substrate of lava rock – the red lava rock in bags you find in the gardening section of the local Lowes. This is very high in iron and is porous enough for babies to live in. Also, if you move the porous lava rocks around in the tanks, you can stir up an extra level of food going to the plants.