A Slightly Different Model for Aquaponics

According to Wikipedia, Aquaponics or pisciponics, is a sustainable food production system that combines traditional aquaculture (raising aquatic animals such as snails, fish, crayfish or prawns in tanks) with hydroponics (cultivating plants in water) in a symbiotic environment. In aquaculture, effluents accumulate in the water, increasing toxicity for the fish. This water is led to a hydroponic system where the by-products from the aquaculture are broken down by nitrogen fixing bacteria, then filtered out by the plants as vital nutrients, after which the cleansed water is recirculated back to the animals.

aquaponics Schematic

Clifford Chin  has a small aquaponics project in Charlotte,NC.  He says

“It’s like growing plants on steroids,” said Chin. “The vegetables grow three to four times faster than what you put in the ground. You can actually eat here on Friday and come back on Monday and see the difference in size.”

Environmentally the basic idea is to have a closed system in which the fish eat the plants. The wastes excreted by the fish are converted by microbes and bacteria into a nutrient that is consumed by the plants.  The plants then are eaten by the fish.  This is environmentally good and sustainable but has no advantage since neither the fish nor the plants could be eaten by humans to remain sustainable.  The modified aquaponics model is to feed the fish with an external supply of food.  The fish grow and at the same time excrete wastes that are converted to plant nutrients that grow the plants that are also eaten by humans.  The advantage is that we get fish to eat and the nutrients from the fish waste efficiently grows plant food that we can eat.  All of this without the use of chemical fertilizers.

There are several disadvantages to this model:

Sustainability of the system depends on the sustainability of the feed for the fish.  Efficient fish growing requires specially formulated feed.  The wastes produced by the fish in a closed aquaponic system go to the feeding of the plants in the system.  The plants are to be eaten by humans not the fish.

It requires growing fish in a recirculating environment that is connected to the plant growing environment.  This is not a simple or inexpensive process. If the climate is not suitable for the fish the process must be grown indoors and that requires energy to maintain the proper temperatures.

A proper balance must be maintained between the amount of fish in the system producing the wastes that provide the nutrients for the plants and the amount of plants needed in the system to maintain proper water quality.  This balance is not always easy to determine.

Growing plants in liquid requires more labor than growing plants in the ground. The faster growth in a liquid environment, however, may partially offset the extra labor required.

A better model is to grow the fish in the most efficient manner possible.  Efficient means growing the fish in an environment that assures the best feed conversion ratios possible, the lowest energy requirements and  high survivability.  The feed conversion ratio is the amount of feed required to produce a pound of fish.  The growing environment must also allow for the capture and removal of the fish wastes from the water.  A recirculating environment is the most efficient fish growing environment achieving very low feed conversion rations and low energy costs.


The manure from the fish can be captured and removed from the water in these systems. The manure is de-watered and dried to about 65% moisture. It is then combined with a carbon source, inoculants and a small amount of clay and decomposed in a controlled process into humus compost.  The resulting humus compost is a complete organic fertilizer that can be stored and shipped anywhere for growing  organic crops.

composting humus compost

Humus compost is a more efficient form of compost.  More organic matter is bound to the clay particles and will not be converted into carbon dioxide as is the case with regular compost.  The organic matter in a recirculating aquaponic system will also decompose into carbon dioxide in a few months. Humus compost is a better form of the fish nutrients and it also makes a smaller carbon footprint since more carbon is sequestered in the soil when humus compost is used.

The consistency of the final fertilizer product is coloidal and putty-like.  It is moist and will form a ball if compressed.  It will readily mix in water and will form a uniform liquid with suspended particles.  The liquid can be pumped through a hydroponic system or sprayed on crops or soil.  The solid form can applied to the soil as well.

Since the fish production process has been separated from the plant growing process a complex balancing act is not needed.  The amount of organic fertilizer needed in the form of the humus compost made from the decomposed fish manure can be determined for any quantity of plants for any location.  The fertilizer can be delivered and applied.

This model is  more sustainable, environmentally advantageous and healthier than growing chickens, beef or pork.  The feed conversion ratio in a re-circulating environment is 1.6 or less.  For chickens the ratio is 2 and for beef as high as 10.

There are also many health benefits from eating fish.  Most fish feeds are grain based with fish meal or other fish related products added.  Some of the organic fertilizer produced in the above described process could be used to grow the grain.  The use of the organic fertilizer would further improve the sustainability of the system.

Fish manure humus compost is available as Fishnure(TM) at www.fishnure.com. It is available in solid or liquid form.

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