All about aquaponics

Original story by Trevor Cochrane, The West Australian

Knowing where your food comes from is very important these days, as is producing your own food. With world trade agreements allowing countries such as China, Vietnam and Taiwan to ship fish products into Australia we can certainly get it at a cheap price. The problem is we don’t know what’s gone into producing the fish we are eating.

I always buy local when it comes to seafood but in recent years I’ve become addicted to another form of fresh fish supply that ties in beautifully with my love of gardening.

In nature, forests surround streams and water trickles through the branches and roots making its way to the stream, cleansed of any toxins or excess nutrients by the roots and microscopic bacteria (called nitrite bacteria) that absorb these nutrients (mainly ammonias) and turn them into plant food absorbed by the tree roots.

The roots filter the water’s edge as well, absorbing the waste products of the aquatic creatures in the water.

The stream flows and gravel on its bottom is an important home for the nitrite-fixing bacteria that absorb excess ammonia nutrient. The total effect is pure clean water, a pristine environment for fish to live in.

Ponds are a popular sight in domestic gardens, and many people introduce plants and some form of filtration process, either mechanical or biological, to help filter the water of unwanted impurities.

Hydroponics is another increasingly popular growing technique that effectively uses water to grow plants – mainly edibles – for commercial production. Most of us who shop at a supermarket enjoy lettuce and tomatoes that are grown this way.

It’s a system that’s incredibly productive and utilises liquid fertilisers to maintain the plants’ growth, with those fertilisers converted into plant food by the same vitally important nitrate-fixing bacteria.

Some people don’t like this because of the synthetic fertilisers used and would prefer a more organic approach to hydroponics – this is where fresh fish excreta can come in handy.

So why not combine aquaculture and hydroponics, creating a system to produce your own edible fish at home as well as freshly grown greens?

Well, you can – it’s called aquaponics.

How it works

It’s not exactly a new idea; humans have been doing this in various forms for thousands of years, starting with the most recognised early form of aquaponics being managed by the Aztecs. They created artificial floating islands called chinampas in lakes that grew fresh vegetables and provided the perfect clean freshwater environment for an agricultural aquaculture approach around and under them.

Aquaponics is so easy to do these days, with local companies such as Aquaponics WA and Woodvale Fish and Lily Farm specialising in providing kit systems that make it easy to create your own aquaponics set-up at home.

The system involves using a specially designed deep tray for plants to grow in. The tray is filled with a product that looks like gravel but is actually expanded clay. This is necessary because it is extremely porous and makes the perfect home for billions of tiny nitrite-fixing bacteria, the essential and unseen ingredient in the system.

Water is pumped from the base of a water-filled round tank (I have successfully used 500-litre and 1000-litre tanks) into the tray, which is planted with a combination of perennial and annual edible plants.

Water flows from one end of the tray to the other, passing through the expanded clay (called hydroton) and plant roots that are growing through it. By the time it reaches the other end the water has been cleaned of excess nutrients and it flows back into the tank clean.

This is an incredibly waterwise system and uses a lot less water than a vegetable garden. The pumps are also cheap to run, usually less than a dollar a week.

What you can grow

The fish varieties that can be used are endless.

Barramundi, silver perch, trout in winter (rainbow are the best), black bream, cobbler and Murray River cod are just some of the choices.

You can grow yabbies and marron easily in this system and companies like Woodvale Fish and Lily Farm also have freshwater glass shrimp you can grow.

These can be sourced seasonally from Woodvale Fish & Lily Farm and Aquaponics WA.

An aquaponics system is perfect for growing pawpaws, dwarf fruit trees (ideally evergreen such as citrus or avocado) and herbs and vegetables that will come and go as they are harvested with the seasons.

Grow a mixture of edibles and try adding annual salad plants, such as lettuce and rocket, and herbs such as coriander and Italian parsley.

Mix these with perennial fruiting plants such as babaco, pawpaw, dwarf peaches, apples, peaches and nectarines.

Try biennial croppers such as kale, silverbeet, rainbow chard, chives and onions, and don’t forget about perennial berries such as goji berries, jostaberries, strawberries, blueberries and raspberries.

The system can also accommodate a huge range of edible water plants, including taro, watercress, water parsley, magnificent lotus and kangkong, to name just a few.

Aquaponics systems can be incredibly productive. My home system produces a crop of 20 trout through winter that start as fingerlings and end up 500-750g, then 15-20 barramundi — all about 1kg — through the summer months.

We’ve grown marron and yabbies extremely successfully and the best thing about the system is we know exactly what went into producing the food.

The vegies, pawpaws and other produce are pristine because they are kept off the ground away from pests and you can struggle to harvest enough at times as the better the water quality, the greater the plant density.

Expert advice

The main suppliers of aquaponic systems in WA are Aquaponics WA in Canning Vale, Backyard Aquaponics in Jandakot, and Woodvale Fish & Lily Farm in Woodvale.

The Department of Fisheries also has plenty of tips on its website. Go to fish.wa.gov.au/Sustainability-and-Environment/Aquatic-Biosecurity/Pages/Keeping-Fish-As-A-Hobby.aspx.

The cost?

According to Erica Roberts, from Aquaponics WA, basic starter kits are priced from about $700.

Tip:

In highly productive systems where you are pumping through crops of fish in big numbers, or where your fish get really big, you may need to combine the biological filtration of plants with a separate mechanical filtration process and this is where talking to an expert really helps. Water management is key and the monitoring of your system is the only technical part of the process of keeping aquaponics.