Growing Fish in a Swimming Pool Aquaponics System : our story

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fish in the pool

This story began on the 6th of December 2014. Location Far North Queensland, Australia. We had ordered 250 Jade Perch fingerlings from a fish farm several hours drive away, and this was the day we arrived back home from picking them up.

This article has been authored by the owners of this site. No input or information has been generated by any AI systems.

We were pretty excited. Finally….we could stock the pool.

This is our story of growing this lot of fish from fingerlings to harvest.

Read on to follow along with the challenges, discoveries, lessons learned, and the evolution of the whole system and process. It’s been a bunch of fun, heaps of challenges, education, and satisfaction.

Raising Fish in a Backyard Pool.

We have a lot to be thankful for.

We undertook a Permaculture Design Certificate course (PDC) about the time we ordered the fingerlings. It was during this course that we recognized the opportunity that we had; to really “dive in” (pun intended) to the world of aquaculture.

Bill Mollison was still with us all, and we took what he had to say seriously. He was a big believer in raising protein in water and aquaculture in general and laid out his case for the process with evidence and conviction.

We just happened to have a pool that we wanted to change to fresh water from salt chlorine, and his information convinced us to start the conversion with the goal of supplying protein in a few short years.

We studied the different methods being discussed across the internet with intense attention. This was the biggest project we had committed to in our journey with Permaculture.

fingerlings arrive home
250 Fingerlings in a bag. Cherry tomato for comparison.

We decided to place bell siphon grow beds around the pool’s edge once the fish grew large enough to support some plants.

The pool is about 50 000 ltrs, and with 250 fingerlings, we had no idea how long it would take to arrive at the grow bed stage. We were flying by the seat of our pants.

We religiously measured and monitored the water chemistry for ammonia, nitrates, pH, and alkalinity. This was fun, very experimental, and oh so educational. The pool evolved before our eyes into a thriving ecosystem. You might have a question of what became of the existing filter system… this article explains all of that separately.

We had water plants that sat on the pool ledges that frogs enjoyed. Dragonflies continuously laid eggs, and when ready, they would climb out of the water under cover of darkness and transform into adults.

We put some smaller rainbow fish in to control mosquitoes, and they bred prolifically……..really…. prolifically.

Into the second year or so, at night under torchlight, I swear that you could almost walk across the pool on their backs without getting wet.

It was an incredible time. Into the second year, we had the grow beds up and running. We built them out of recycled hardwood scrounged from all sorts of places.

We liked the look; the wood could sit on the edge of the pool without leaching harmful chemicals into the pool. This would be what I could now call the golden period for the pool and its inhabitants.

The jade perch were now growing at a reasonable rate.

6 month old jade perch
Getting Bigger

Growing your own Fish Food.

The fish farm we got the fingerlings from supplied us with some commercial fish food that lasted for a while.

I don’t remember exactly how long, but during the time it took to use it up, we researched how to feed them with as little an impact on the environment as possible.

What I mean by this is we rejected the notion of hard feeding the fish to fatten them up within 12-18 months, basically.

Jade perch are voracious eaters, and when they are hard-fed commercial food, they turn into footballs full of oil. This turned us off on a few levels.

These fish were under our care, just the same as our chickens. They deserve respect, even if the end goal is to consume them eventually. The idea of force-feeding just didn’t appeal to us at all.

Another big issue was that it took 10kgs of wild-caught fish to make less than 1/4 of that in aquaculture pellets, so to us, it seemed madness at an industrial level to do this, let alone for a backyard pool.

We had to feed them as much as we could from the yard.

We trialed many different things with the fish. Our research told us they were omnivores, and while they display that trait when young, we discovered that they adore mango.

They also have a thing for pawpaw.

Fortunately for them, we had two mango trees that bore well, and we couldn’t handle all of the fruit. The fish dined like kings.

Around the yard, we were busy redesigning areas in line with the permaculture design we had developed and filling garden beds and areas with food plants.

One of these plants is Sweetleaf, botanically known as Sauropus androgynus. It turns out that jade perch will almost kill for this plant.

We would strip several branches off of a plant, throw the leaves onto the pool surface, then watch the fish appear from the depths and attack the floating leaves with gusto.

The plant is one of our Hardy Reliables on-site and is a staple of ours and the chickens. It is high in protein and minerals.

By this stage, young rainbow fish were busy chasing dragonflies across the surface during the day and launching themselves out of the water in vain attempts to catch them.

It was like a dog trying to catch a semi-trailer truck. If they caught one, what were they planning on doing with it? The dragonflies were ten times their size.

Waterplants For Backyard Aquaponics.

While everything was progressing nicely, we thought a few water lilies would set the pool off wonderfully, and they did for a while.

I think we saw two flowers in total……before the jades ate them. We had a plant growing in one of the grow-beds called Kang Kong, or swamp cabbage.

We picked it for salad greens, the chickens got a few leaves, and the fish smashed any part of the plant that ventured near the water.

While the rainbows were busy chasing dragonflies, the jades were launching themselves out of the water to pick at the overhanging stems and leaves of the Kang Kong. It was becoming a circus.

Then our first date with trouble arrived.

water chemistry check
Water Testing with grow beds in the background. Large leaf is Taro

Hypoxia in Aquaponics.

Fish breathe underwater. We all know this. But noticing the signs of early onset of hypoxia is not a simple thing to see when you are un-trained and in a constant state of discovery.

Hypoxia is a lack of available oxygen in the water column. We started seeing the odd fish on the surface swimming along while opening and closing its mouth. Oh, look…. we said… it’s eating stuff on the surface.

The next day several fish were carrying on the same way. We said…. oh look…. the words out now; they are all grabbing a feed.

Then the next day presented us with several dead fish floating on the surface. Over that day, we researched deeply and discovered that we had an oxygen deficiency, and the fish were in trouble.

I felt sick.

We sorted out an air pump that could deliver more air to the bottom of the pool. This bought the fish and us a few days while we developed a plan to upgrade appropriately.

In the meantime, several more fish floated to the surface and reminded us of how difficult this task was for the novice.

We had assumed that the returning water from the grow-beds via the bell siphons was oxygenating the water enough for the fish, but the pool, at this stage, was reaching its limit for carrying the amount of biomass we had introduced.

250 jade perch about 4in (100mm) long is a lot of fish. Add in all the rainbows, and we had a live fish soup.

We didn’t understand the situation because the water was a green color, not in a bad way, but it was green. You could see your fingers if you stuck your arm to shoulder depth. We didn’t see the jades during the day.

They kept to the depths and only surfaced at feed time each evening. Lots of fish need lots of oxygen.

Cane Toad Eggs are Poisonous to Fish.

If you have been on this site before, you would understand that we live in the wet tropics of northeast Australia.

This is a big sugarcane growing area, and in 1935 a bunch of well-meaning blokes introduced the cane toad up this way to control the cane beetle.

The brains-trust of the day didn’t do any studies on the potential environmental impacts of introducing them, nor did they even check if the toad would even eat the beetles it was introduced to control.

The rest is history, they say, and the toad is everywhere now…or close to it.

It turns out that cane toads like pools with fish in them. Not so much for somewhere to swim and lay about, but to breed in.

When cane toads lay eggs, they lay them in a long continuous string that they lovingly weave in and around any water plant they can find.

When you get a bunch of them carrying on this way simultaneously, the pool looks like an upside-down Christmas tree, with strings of baubles hanging everywhere.

This was an interesting development. We checked the pool edges each morning after rain for evidence of egg laying. Rain triggers them to breed, and boy…. don’t they go to town.

Many sleepless nights were spent roaming the pool area with a torch, collecting toads and flicking them over the fence onto the road. The mating call still gives me bad vibes.

This, we discovered, was another lesson being delivered by nature. We know that the cane toad is poisonous, and it has several poison sacs that express poison when the toad is in defense mode.

What we didn’t know…and you may not know either, is that the eggs are also toxic. Rainbows (small fish) love eating toad eggs. I wish they wouldn’t, but like a kid in a Lolly shop, they just cannot help themselves.

We sometimes missed a few toad eggs. Often the strings that the eggs were a part of broke off because mum toad had tangled the eggs well and proper around the water plants, so a few times, we discovered a few dead rainbow fish floating on the surface.

Now….remember back up the page a bit where I told you that Jade perch are omnivorous? Well…. it turns out that a dying, poisoned rainbow fish triggers the hunting instinct in the jades.

Yep, you guessed it. The Jades then became sick and died from eating the poisoned rainbows. I had never, in my wildest dreams, ever thought that the toxin of a cane toad could travel up the food chain so easily.

I saw it several times, so I have absolutely no doubt why those fish died. No doubt at all.

Toad exclusion barriers should be considered if you are thinking of putting fish in your pool. It wasn’t an option in our case.

Filtration for Pool Aquaponics.

This is a subject that we will dedicate an entire post to because of the twists and turns that we faced when our system evolved outside of our expected parameters.

We eventually arrived at a wonderful process that allowed us to capture the nutrients and utilize them elsewhere on the property.

That was the original intent when first planning putting fish in the pool. (Aquaponics pool filtration article link)

Just to keep it brief, there are choices to make regarding filtration for your situation and they are as follows.

  • How large your pool is.
  • How many fish do you wish to place in it.
  • The fish species and it’s eating and growth habits.
  • The food type that you intend to feed the fish.
  • Do you intend to supply the food from your site.
  • The site of your pool and the availability of using gravity as a tool.
  • Fish poo end use intent.
  • Natural pool vs mechanical filtration methods.

Only you can answer each of those yourself, so I won’t expand on anything here. I can only share what we discovered as we progressed with our system.

You will find that many processes are stand-alone items and are not applicable to all components of any one system. It can be quite convoluted and complex…. if you let it.

We like simplicity. We want reliability, and we like results. We will get to those when the dedicated post is up.

Harvest Time.

The decision to harvest was forced upon us by nature…. or more accurately, a nightly visit by a White-Tailed Rat that developed a taste for jade perch.

Before we started catching them, we were coming across half-eaten fish carcasses in all sorts of weird places in the yard for a week or two prior.

It was only by pure chance that we saw the thief in action late one afternoon and promptly set a trap.

We caught the suspect and removed it from the site, and the problem stopped. The fish were now large enough to take and were over five years old.

We had lost a fair number along the way through the hypoxia event and natural causes, so we guessed there were maybe half left in the pool. It was time.

jade perch in a cast net
Jades and rainbows at harvest time.

The end goal had arrived, and we were in two minds about how to go about this.

For over five years, we had worked with these fish, fed them, and done our best to give them as natural a setting as we could within the confines of a concrete in-ground swimming pool.

Overall, I think we succeeded. Getting them out of the pool proved a challenge, but once they were removed, the challenge of processing them was now our focus.

We found that a cast net was the best method, but the last few fish proved very elusive. We have cooked a few in different ways and canned (bottled) about 90 Jade Perch for storage.

We will put up a post on that when time permits.

Conclusions

Growing fish in a backyard pool is definitely achievable. I would not recommend approaching it as we did for several reasons that are only from hindsight.

The primary thing to consider is the biomass load you are prepared to work with. Higher loads will take closer monitoring and have less safety buffer if things go pear-shaped.

A few fish should be a simple task with research and practice.

Would we do it again?

Not in the format we used. For our situation now, the pool is being reconverted back to a swimming pool for family reasons, but it is now a freshwater pool with UV attached to the filtration system.

This allows for very low usage of chemicals.

In closing, I hope you have gained some insight into the problems of putting fish in a backyard pool.

It is not a simple task, but thanks to the internet, there are pockets of good relevant information for us to learn from and consider. Contact us if you have any questions, and we can get back to you with any information.

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Article by Tim Blanch for TheTropicalHomestead.com. He is a qualified Permaculture designer.