Profitable commercial aquaponics is doable. It's success depends on several factors. They include system design, market, what you plan to grow and operating costs, among others.
There are several different designs currently being touted and which one you choose depends on how much horizontal space you have to grow and whether you grow indoors or in a greenhouse. Indoor growing has the advantage of growing a consistent crop year round. This can produce out-of-season vegetables, which can bring a premium price, especially in colder climates.
The down side to indoor growing is the initial cost of purchasing the grow lights and the electricity for their operation.
What you grow and the market are linked and depends on your location relative to population centers and the particular clientele. In some areas, certain types of vegetables may be more to the liking of your down-line customers. Local farmer's markets are seasonal in many places and year round in others. Local private chefs or restaurants may be a good outlet for your higher end product. CSAs (community supported agriculture) are another way to go in selling your vegetables. Then there are the local food markets that may be willing to sell your produce, depending on your competition. Your own roadside market is a great way to retail your product, if that can be done.
If you can grow year round in a greenhouse then you will need to be in a moderate to warm climate. In colder areas it is possible to grow year round if you have a climate controlled greenhouse. These generally have ferruling curtains to retain heat at night and on stormy days with no sunshine. If you plan on heating the greenhouse in this climate then that cost will have to be part of your accounting.
Summer cooling of the greenhouse is important regardless of the climate, as there is generally a 30 Fº temperature rise in the greenhouse over the outside temperature while the sun is shinning.
In both cases it is advisable to have your fish tanks and processing area in an adjacent separate inclosed building that is climate controlled.
In milder climates your operating costs are mitigated by the use of a greenhouse. Depending on system size, labor can be supplied by family, as in a mom and pop operation. This can be done up to about 5,000 to 10,000 square feet of growing area.
In a properly designed commercial AP system the revenue from your veggies (be they leafy greens) will account for about 95% of total fish and plant revenue. This is due to the fact that in a system where all fish waste is properly mineralized, each pound of fish in the system can grow about 15 leafy green plants in various stages of growth as long as the fish are being fed a grow-out diet. This has been substantiated by Dr. Wilson Lennard and myself.
While it might take as much as 39 weeks to grow out a tilapia to around 1.25 to 1.5 pound of fish weight, you will be growing out about 97 heads of leafy greens based on a 6 week plant cycle.
These leafy greens are of a high quality and should fetch a good price, either wholesale or retail.