Fish farming and fruit and vegetable farming do not at first glance appear to be natural bedfellows. Sure, you can do one, you could even do both if you had the time, but to combine them into one joined-up system, surely that’s nonsense? Maybe not – The relatively new science of aquaponics is showing how it can be done.
The word aquaponics is a hybrid of aquaculture (fish farming) and hydroponics (growing plants in water rather than soil). It brings these two elements into a single system which is beneficial to both plants and fish.
Let’s look at the aquaponics angle first. Fish are pretty easy animals to keep. Keep them well fed, don’t overstock the pool, and make sure the water is aerated, and they’ll thrive. The main concern is keeping the water clean. Fish produce urine and faeces like any other animal, and in a closed system like a pool it builds up and pollutes the water. So the water has to be filtered to remove this waste.
Fish waste, just like cow manure is rich in plant nutrients, so it seems a shame to just chuck it away. This is where the hydroponics bit comes in…
Hydroponics is the process of growing plants in water. It delivers nutrients to the plant root more quickly than soil and produces a large crop, but the water does have to be supplied with nutrients to help the plant grow. It’s a popular method for growing salad crops and soft fruits.
Eureka! Why not combine an aquaponics system which has plenty of nutrients in water, with a hydroponics system? The water from the fish tank, complete with fish waste, is pumped to the plants; the plants remove the waste from the water and grow; the water is now clean and can be returned to the fish tank. It’s a closed system, with very little wastage. Water is only lost through evaporation, and the fish can even be fed on some of the plants.
The plants roots are bathed in the water by one of three methods[1]: by floating on a raft (deepwater circulation); by sitting in pots bathed by a thin film of water running down a gulley (nutrient film); or by sitting in grow beds of gravel.
Aquaponics is still in its infancy but there are many small-scale test projects taking place around the globe. If it lives up to its promise it could develop into a major farming method and benefit many communities by providing fruit, vegetables and protein at a very low cost. -MARK LEE