Mixing aquaculture into the management of fruit trees was an after thought for me but has worked so well that I think it is worth considering for anyone who has a small orchard as it improves the nutrient quality of the water and creates an additional by-product of fish whilst giving water a second use and removing it’s chlorine which adversely affects the soil microbial life.
When most people consider adding edible fish to their backyards they immediately think of aquaponics as the only way to do this, the problem is that as much fun as aquaponics is it can be a difficult learning curve and I have seen a lot of people who have tried it and then given it up when it became too hard or they lost some fish. You do have to enjoy the tinkering involved with keeping a system balanced and healthy and it can become a full time hobby in itself.
A much simpler alternative that can produce just as much fish and similar vegetable hauls is to use simple run to drain aquaculture by setting up a water tank to house your fish in and then using that tank for all the watering that you were already doing in you’re yard.
Once you have finished watering top you’re tank up again and the fish will be just as happy as if you had scrubbed their water clean with aquaponic flood and drain grow beds. This method works particularly well as a water/nutrient supplier for fruit trees and if you incorporate a large number of wicking beds then you are able to get similar water efficiencies to aquaponics at a far smaller cost especially if you were able to pick up a free water tank and patch any holes it might have which is my preferred tank acquisition method.
The picture below shows where I have added a through-tank tap fitting that will take a regular garden hose to one of my tanks. The water is gravity feed out to the plants and just trickles out the other end at a slow rate which means that none of the water is wasted as it has time to filter into the ground around the roots of the plants without running off. When I am working in the yard I just go over occasionally and move the hose to a new location.
It is ABSOLUTELY ESSENTIAL that you put the tap fitting no lower then half way up the tank otherwise you may one day forget that you left it on and all your fish will die. The other important thing to remember is that the air lines must be placed right at the bottom of your tank otherwise the fish will run out of oxygen when the waterline falls below their air bubbler level.
You should also select a hardy fish species that is use to rising and falling water levels and living in small pools of water whilst they wait for the next Aussie wet season to hit. I use Jade and Silver perch but Sleepy cod might also be a good choice. I don’t believe that this technique would work with Barramundi but have never tried it. Spangled perch are likely to breed in tanks but I haven’t tried those either and don’t know what they taste like.
One other thing that you must add is some sort of backup air supply in case the power fails. This can either be a backup bubbler or bilge pump that sprays the surface or a solenoid valve connected to mains water that gently but vigorously sprays the surface of the tank to break the surface tension.
The return water inlet that tops the tank backup with water can also have a float valve like in a toilet that switches the town water off once the tank has been filled up again. I preferred to take out what water I need before turning on the tap to refill the tank as it reduces that amount of chlorinated water that makes it to the plants. The inlet valve must be at the top of the water tank to prevent the tank from being syphoned dry if the connecting hose is removed from the mains water tap.
With a bit of scrounging your aquaculture watering tank can end up costing very little money and certainly much less then many aquaponic systems and if done properly there is no reason why you should be using anymore water than you would have before with your regular plant watering schedule the only difference will be that the water will be much better for the trees!
There is one caveat that I must include about directly filling your tank with town water. It is well known in aquaponic circles that adding town water directly into an aquaponics system is a major no-no. The reason for this is that chlorine in the water will kill off the bacteria that is necessary in the nitrification cycle of the system. This means that the plants will grow less vigorously and the ammonia won’t get taken out of the closed loop system which will end up killing the fish. This is not a problem if you are using a run to drain system however as you are not dependent on recycling the water for the health of the system. You must however consider if the level of chorine will have any impact on the fish in your tank. I live in a small town that is a very long way from the water treatment plant in Rockhampton and the chorine levels seem substantially diminished by the time they reach us. I have done a large number of cycles of the tank without any losses of the fish due to water quality.
I have also noticed that the fish feed much more vigorously after the water has been changed and it seems to have gotten rid of some fluke parasites that were in my aquaponic fish before I started adding the chlorinated water to the tank.
If you are concerned about the levels of chlorine in the water then you should use an intermediate dechlorination tank, even a cheap food grade IBC container will do the job. It doesn’t take long for the chorine in town water to evaporate off especially if the water is spayed into the tank as a fine mist.