Aquaponics proponents rarely mention that you have to feed the fish. The fish are essentially filters that reduce other matter (mostly other fish) into nitrates. An efficient system would remove these inefficient filters and add nitrates directly to the soil.<p>Yes, you can eat the fish.  But it takes 240 days to raise (feed) a tilapia to 1 lb of weight. There are cheaper and faster sources of protein. For example, soy beans take 45-100 days and yield .25lb of pods per plant.