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On average, only 1% of the Sun’s energy falling on vegetation results in vegetables: 1,000 kilocalories of light energy can produce 10 kilo calories of vegetables. On average, fish can obtain only 10% of the energy utilized by plants. Thus energy eaten by humans is on average only 1% of the total. This tells us that we would get the most food energy from a pond area eating the algae rather than growing fish. The first step in the food chain is to eat an edible species of algae such as Chlorella sp. The next step would be to raise plant eating fish. The last step would be to eat carnivorous fish, which are most fish species. Typically the amount of energy from eating a carnivorous fish like the catfish is only 670 calories from an original outlay of 2,700 calories, only 25% of the calories. Thus, by eating carnivorous fish there is yet another loss in energy.

For an algae/fish pond, the food cycle is as follows. Raw sewage is added to the algae pond. It has a surface are of 225 square feet, 15 feet by 15 feet, figuring solar input at 90,000 kilocalories per day, with a photosynthetic conversion rate or 3% yielding 2,700 kilocalories or about 5000 grams of algae. This is then fed into the Zoo Plankton pond which also has a 15 by 15 foot surface. The biological conversion here is 25%, a yield of about 670 kilocalories a day in Zoo Plankton or about 135 grams of protein, down to a quarter of a pound. This is then fed to the catfish pond. The pond volume here is 300 cubic feet. Since the biological conversion in this last step is 10% you only get about 14 grams of catfish per day.

Realistically, you’re not going to live on a fish culture unless you are talking about really big ponds and lots of sunlight. You can increase this with intensive aqua culture, but even so you are looking at a maximum of 25 pounds of fish per year with the above setup.