National Geographic 08.2019

Fish food

Nitrobacter

(bacteria)

Nitrosomonas

(bacteria)

Nitrite

(toxic)

REARING

TANK

FILTER

TANKS

AIR

PUMP

Tilapia

(Oreochromis

aureus)

Nitrate

(nutrient)

Ammonium

(toxic)

ILLUMINATING THE MYSTERIES—AND WONDERS—ALL AROUND US EVERY DAY

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Fish, such as the highly

adaptable tilapia,

excrete toxic ammonia

in liquid waste.

Fish waste falls

to the bottom of

the rearing tank.

Two to four gallons

of water support

a pound of fish.

Solids settle, then

are collected

for fertilizer.

Pumped air stirs

and oxygenates

the water.

Plastic pieces are added

to provide surface area

for naturally occurring

bacteria to grow on.

Solid waste is filtered

out; it can be used as

fertilizer for crops grown

traditionally in soil.

A two-step bacterial

process turns harmful

ammonia into nitrates,

12 3nutrients for plants.

FROM TANK TO TABLE

VEGETABLES GROWN THROUGH AQUAPONICS—a combination of fish

farming (aquaculture) and plant cultivation without soil (hydro-

ponics)—may be coming to a marketplace near you. Practiced by

the ancient Chinese and by the Aztec, the ever evolving technique

is going commercial in Europe, Canada, and the U.S. It’s being

eyed as a sustainable farming option well suited to cities, islands,

and developing regions where water and land are in short supply.

26 NATIONAL GEOGRAPHIC