Why should you care?
Aquaponics (AP) is easy and has been used for thousands of years (from Chinese rice paddys to the Aztec water gardens), can be practiced on any scale, consumes approximately 1% of the water in a traditional growing system, and is a great way to learn about closed-loop systems and ecology.
AP can help feed families in dire need of nutrition, with agricultural crops; but also with much needed proteins in the form of fish. This example isn't exactly what a poor family in a third-world country might put together, it is exactly as stated; an example.
The entire earth is (more or less) a giant aquaponic lab; but we're going to start small, in the living room.
Step 1: What You Need
Rubbermaid Roughtote 18-gallon storage bin.
~18-gallons of water
~8-gallon "under bed" style tote.
~8-gallons of "pea gravel"
~4-ft of 1/2" tubing
End cap for tubing
~200-gallon/hr water pump with control valve (less is probably fine with a system this small)
On/Off timer with 15-minute intervals
Freshwater aquarium water tester (strips or kit)
Fish (I used 3 goldfish and a crayfish)
Seeds for planting (Fruiting or non-fruiting, lettuces, wheatgrass, it's all good)
Short stand or table that can hold ~80lbs or more.
If you had to buy everything for this as new, it would probably cost ~$30US including the fish and seeds but excluding the stand/table and test strips. As it is I had everything on hand except the pea gravel, so this cost me about $0.75 to make.
Options (not necessary for the purpose of this Instructable, but very valuable additions to AP in general):
Uninterruptable Power Supply (battery backup)
Grow lights, CFLs work fine (if growing away from sunlight)