Aquaponics – SS3 Horticulture and Crop Production Lesson Note (First Term)

Aquaponics is a closed-loop farming system that combines fish farming (aquaculture) with growing plants in water without soil (hydroponics).

Behavioural objectives

1. Define aquaponics and name the two types of farming it combines.
2. Describe the four steps of the aquaponics cycle.
3. List the four main parts of a basic aquaponic system and state the use of each.
4. State the advantages and limits of aquaponics.
5. Explain why the numbers of fish and plants must be balanced.

What is aquaponics?

Aquaponics is a closed-loop system in which fish waste feeds plants and the plants clean the water for the fish.

• Aquaculture: raising fish in tanks.
• Hydroponics: growing plants in water without soil.
• Closed loop: the same water is used again and again, with little added or lost.
• Bacteria: tiny living things that turn fish waste into plant food and make the exchange possible.
• Idea behind it: nature recycles everything, and aquaponics copies this by letting each part help the others.

What is the difference between aquaculture, hydroponics and aquaponics?

Aquaculture is the farming of fish and other water animals in tanks or ponds.

Hydroponics is the growing of plants in water with dissolved nutrients and no soil.

Aquaponics joins the two so that one water supply serves both fish and plants.

How does the aquaponics cycle work?

The aquaponics cycle is a continuous circle in which water moves from the fish to the bacteria, then to the plants and back to the fish.

1. The fish produce waste: fish release waste, mostly ammonia, into the water as they eat and grow. Too much ammonia is poisonous and can kill the fish.
2. The bacteria change the waste: nitrifying bacteria live on pipes and growing media. They turn toxic ammonia into nitrites, then into nitrates.
3. The plants take in the nitrates: plant roots absorb nitrates as food, which helps the plants grow.
4. Clean water returns: the plants have removed the nitrates, so the water is clean. It is pumped back into the fish tank and the cycle starts again.

What are the parts of an aquaponic system?

A basic aquaponic system has four main parts: the fish tank, the grow bed, the water pump and the aerator.

• The fish tank: holds the fish. Tilapia and catfish are common because they are hardy and grow fast.
• The grow bed: holds the plants. It is filled with clay pebbles or gravel that support the plants and give bacteria a place to live.
• The water pump: moves water from the fish tank to the grow bed.
• The aerator: an air pump that bubbles oxygen into the water, because fish and plant roots both need oxygen.

What are the types of aquaponic system?

There are three common types of aquaponic system: media bed, nutrient film technique (NFT) and deep water culture (DWC).

Media bed

• Set-up: plants grow in a bed filled with gravel or clay pebbles.
• Use: the media also hold the bacteria, so it suits small farms and school projects.

Nutrient film technique (NFT)

• Set-up: a thin film of water flows along channels or pipes holding the plant roots.
• Use: it suits small, light plants such as lettuce.

Deep water culture (DWC)

• Set-up: plants sit on floating rafts with their roots hanging in the water.
• Use: it is common in larger systems that grow leafy vegetables.

Which crops and fish suit aquaponics?

Fast-growing leafy vegetables and fruit vegetables grow well in aquaponics, together with hardy fish.

• Fish: tilapia and catfish.
• Leafy crops: lettuce and spinach.
• Fruit crops: tomato, pepper and cucumber.

What are the advantages of aquaponics?

Aquaponics is often described as a sustainable way of farming because it saves inputs and gives two products.

• Two crops, one space: fresh vegetables and fish are harvested from the same system.
• No chemical fertilisers: fish waste supplies the nutrients, so the farmer buys less fertiliser.
• Little water waste: water is lost only through plant uptake and evaporation, so it uses much less water than soil farming.
• No weeding or digging: plants grow without soil in raised beds, so there are no weeds and less bending.
• Fast growth: plants get a steady supply of nutrients, so they often grow quickly.

What are the disadvantages of aquaponics?

The main disadvantages of aquaponics are cost, dependence on power and the skill needed to run it.

• High start-up cost: tanks, pumps, pipes and grow beds are expensive to set up.
• Power needed: if the pump or aerator stops for long, the fish can die from lack of oxygen.
• Skill needed: the farmer must understand fish, plants and bacteria together.
• Chemical limits: pesticides that harm fish cannot be used on the plants.

Why must an aquaponic farm be balanced?

An aquaponic farm must be balanced because fish, plants and bacteria depend on one another.

• Too many fish: they produce too much waste, the plants cannot keep up and the water becomes dirty.
• Too many plants: they run short of nutrients and their leaves turn yellow.
• Temperature: tilapia like warm water, but some plants prefer cooler conditions, so the farmer chooses a middle range that suits both.
• Bacteria: they need oxygen and surfaces to live on, so the aerator and grow bed must work well.

Evaluation

1. Define aquaponics and name the two types of farming it combines.
2. What is the work of nitrifying bacteria in an aquaponic system?
3. List the four main parts of a basic aquaponic setup.
4. State three advantages of aquaponics over soil farming.
5. What happens when an aquaponic system has too many fish?

Assignment

Draw a simple diagram of the aquaponics cycle, label the fish tank, water pump, grow bed and aerator, and write three lines explaining how the water stays clean.