Aquaponics is based on productive systems as they are found in nature. It can be loosely described as the combination of aquaculture and hydroponics and this is where the name aquaponics originates.
Hydroponic systems rely heavily on the careful application of man-made nutrients for the optimum growth of plants. The nutrients are made from mixing together a concoction of chemicals, salts and trace elements to form the ‘perfect’ balance. Water in hydroponic systems needs to be discharged periodically, as the salts and chemicals build up in the water, which becomes toxic to the plants. Aquaculture systems focus on maximizing growth of fish in tank or pond culture.
The fish are usually heavily stocked in the tanks often 10kg in 100L of water. The high stocking rates often mean that the tank water becomes polluted with fish effluent, which gives off high concentrations of ammonia. Water has to be discharged at a rate of 10-20% of the total volume in the tank once a day, everyday. This water is often pumped into open streams where it pollutes and destroys waterways.
Aquaponics combines both systems, and in doing so cancels out the negative aspects of each. Instead of adding toxic chemical solutions to grow plants, aquaponics uses highly nutritious fish effluent that contains almost all the required nutrients for optimum growth. Instead of discharging water, aquaponics uses the plants and the media in which they grow to clean and purify the water, after which it is returned to the fish tank. This water can be reused indefinitely and will only need to be replaced when it is lost through transpiration and evaporation.
**Is Aquaponics Complicated?**
It’s as simple as it seems, pumping nutrient rich fish water past the roots of plants, which extract the nutrient from the water. The principal method we deal with here is using grow beds filled with a medium, whether it’s gravel, river stone, crushed basalt, or expanded clay. Plants are grown in the media filled beds and water is pumped from a fish tank into the grow bed, draining through the gravel, and back into the fish tank.
Experimenting with aquaponics can be as simple or as complicated as you like. It could be as simple as an aquarium on a sunny windowsill with some goldfish, with water pumped into some gravel filled pots above it, draining through the gravel back into the aquarium. Once you have tried something simple you can progress up to a system with multiple grow beds and high stocking densities of fish.
There are three basic styles of aquaponic systems, which we discuss below in a little more detail.
**Media Filled Beds**
Media filled beds are the simplest form of aquaponics; they use containers filled with medium of expanded clay or similar media. Water from a fish tank is pumped over the media filled beds, and plants grow in the rock media. This style of system can be run two different ways, with a continuous flow of water over the rocks, or by flooding and draining the grow bed, in a flood and drain or ebb and flow cycle.
**NFT or Nutrient Film Technique**
Nutrient Film Technique is a commonly used hydroponic method, but is not as common in aquaponic systems. In NFT systems, nutrient rich water is pumped down small enclosed gutters. The water flowing down the gutter is only a very thin film. Plants sit in small plastic cups allowing their roots to access the water and absorb the nutrients. NFT is only really suitable for certain types of plants, generally leafy green vegetables. Larger plants will have root systems that are too big and invasive, or they become too heavy for the lightweight growing gutters.
**DWC or Deep Water Culture**
Deep Water Culture works on the idea of floating plants on top of the water allowing the roots to hang down into the water. This can be done in a number of ways. This method is one of the more commonly practiced commercial methods. DWC can be done by floating a foam raft on top of the fish tank. However a more common method is to grow the fish in a fish tank and pump the water through a filtration system, and then into long channels where floating rafts filled with plants float on the water surface and extract the nutrients.
**Which Style is Best for Me?**
So there are the basics of aquaponics. It really can be as simple or as complicated as you like. If you want to start off small and simple take a piece of polystyrene, cut some holes in it, stick some mint cuttings or water cress cuttings through the holes, and float it on the surface of an aquarium or pond. Within no time you’ll end up with a mass of floating herbs, and you’ll have cleaner water for your fish. Through lots of experimenting over the years, and through the trials of members on the online discussion forum, the flood and drain media based system has been found to be the most reliable and the simplest method of aquaponics, especially for beginners. It can be done very simply using a wide range of different containers. The flood and drain media bed system also requires minimal maintenance.
**The Nitrogen Cycle**
One essential unseen element to an aquaponic system is beneficial bacteria. The bacteria flourish in the dark moist gravel filled grow beds, and break down elements in the water into a form which the plants can absorb and use. An aquaponic system is organic due to its very own nature. Synthetic fertilizers can’t be fed to the plants or it will adversely affect the fish and the beneficial bacteria. The system has to be kept natural.
There are two different bacteria that break down wastes from the fish: the first is Nitrosomonas, which converts ammonia into nitrites. These nitrites are then converted into nitrates by Nitrobacter bacteria; the plants can then consume the nitrates to grow.
One interesting aspect of aquaponics is that it’s a self-balancing system to a great extent. As more nutrients become available through increased feeding of the fish, plant growth rates will increase to consume the extra nutrients. When fish are smaller or if the fish aren’t being fed as much feed growth rates of the plants will slow down accordingly.
Recycled containers like IBC International Bulk Containers, as well as second hand plastic drums and other similar equipment are commonly used by people to build aquaponic systems. This is done for many reasons: recycled materials can generally be found around the home, or sourced from salvage outlets fairly cheap, so you can build quite a large system for very little initial cost. Just be careful when using second hand materials. It’s useful to know what has been stored in containers before you decide to use them.
But really, there’s no excuse not to give aquaponics a go. If you feel a little unsure about starting and you want to make sure you get the best head start, then you can look at starting off with a kit system.
If you’re a handy person who prefers trying to build something from scratch, then keep your eyes peeled on refuse collections and at salvage retailers. Bathtubs are ideal for aquaponic growbeds, and they have drain fittings preinstalled.
**Importance of Fish**
Fish are the powerhouse of an aquaponics system. They provide the nutrients for the plants and if you’re growing edible fish, then they also provide protein for yourself. Keeping fish may be a little daunting to some, especially those without any prior experience, but you shouldn’t be discouraged. Keeping fish in an aquaponic system is simpler than keeping aquarium fish, so long as you follow simple guidelines. Then growing fish from fingerling size to ready-to- eat fish can be extremely simple.
**Choosing a Fish Species**
There are many different species of fish that can be used in an aquaponic system, depending on your local climate and available supplies. Our local climate in Perth, Western Australia, allows us to keep Rainbow Trout through winter, then a warmer species like Barramundi during summer. There are also a few choices for year round fish that we could grow, but they often take a longer time to mature. If you live in a cooler climate you might be looking at growing Trout all year round, or perhaps another locally produced fish species. In warmer areas of Australia people generally grow Barramundi, or Jade Perch year round. In most warm areas throughout the world Tilapia is the fish of choice.
You should take a few factors into account when deciding what the best species is for you to grow. The most important question is what do you want from your system. If you don’t want to eat your fish then you probably won’t want to grow edible fish, or you may want to grow an edible fish that can live year-round in your area, so that you’re not having to harvest fish out seasonally. The second most important factor is ‘What’s available?’ You need to be able to buy fish to stock your system, even with species such as Tilapia that breed readily. You need to get your broodstock in the first place.
Here’s a list of useful aquaponic species with a few details about each –
There are other fish species, which are quite suitable for aquaponics that might be available in your local area. In Europe many different species of carp are grown; within the United States such species as Bluegill are often available, while in Australia we also have a number of other native species like Sleepy cod, which would be suitable.
Other aquatic animals that can be incorporated into an aquaponic system are fresh water mussels, fresh water prawns, and fresh water crayfish. Mussels are a filter-feeder, and do a great job of helping to clean the water. They will happily grow in flooded grow beds, or can be incorporated into fish tanks. Crustaceans make a nice addition to an aquaponic system and there are a few different species available depending on your location and water temperatures.
For those in tropical areas there’s Redclaw, a fast growing native Australian species, and for those in cooler areas there’s Yabbies or Marron.
Yabbies breed readily, given the right environment and the correct water temperature, as well as long daylight hours. They also grow fairly quickly, but they can be prone to fighting and cannibalism when stocked very densely. The Yabby is also an attractive crustacean.
To be continued in the next issue.