Growing Sustainable Fish Food for Aquaponics. (success)

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jade perch fingerling at 4 months old

Aquaponics can be very rewarding. The acquired skills and the produce that can be grown make the initial cost and effort worth the investment. The entire process becomes an active biology and chemistry lesson when an aquaponics system is set up correctly, and the fish are settled.

Some people describe it as a closed loop system, but it will never be until you can supply food to the fish at no cost from your property.

Growing plants intended for fish food may not be available for some yards, but if you have space for an aquaponics setup, you probably have space for gardens.

We are fortunate to have had the space, and our intention was to use plants already on site.

Our experience was not based on a put-together system but a 50 000-liter swimming pool stocked with 250 Jade Perch.

As the fish grew in size, this system slowly evolved from an aquaponics system into an aquaculture unit.

This process took 5-6 years to reach the final harvest. Over that time, we supplied a large percentage of the food to the fish from the property and this is what this post is about.

What plants will fish eat in Aquaponics?

  • Rosella leaf. This is a hibiscus.
  • Grass clippings. We use zero chemicals.
  • Sweetleaf, also known as Katuk.
  • Kang Kong. This grows alongside the pool.
  • Mango fruit. Excess fruit from the seasons harvest.
  • Papaya fruit. Again, excess fruit.
  • Green tree ant larvae.

This list is not exhaustive but represents what we found Jade Perch will happily take. The fish become omnivorous over time, so we have included the ant larvae.

Mango fruit.

We have two mango trees in our yard, and they can overwhelm us with fruit some years. It was on one of these bumper years that we found a use for the excess fruit that had dropped before we could pick it.

Some of this fruit was also damaged by insects and had larvae inside the fruit, so that was a protein bonus.

We sliced the mango in half and held it in the water, and the fish ate heartily. This happened while the fish were relatively young.

We would drill a hole through the seed of the mango and poke some wire through it to hold it from sinking to the bottom of the pool. This was when the fish were larger and far shyer in the latter years.

Jade perch eating mango
These fish have expensive tastes. That is a mango.

Papaya fruit.

This fruit can be grown without much input from the gardener if there is a dry, sunny spot and the winters don’t get too cold.

We have several plants here, and we most always had fruit to spare. The fruit was sliced into sections and dropped in the water. It floats, and the fish hammer it. It is high in nutrients and works well with the fish.

Because the pool volume was significant, we have no information on what feeding these fruits do to the water chemistry, but if the fish eat all of the fruit, there should be no problems.

Just don’t leave something that they don’t find attractive at the bottom of the tank. (How we grow enough to feed the fish here.)

Rosella leaf.

Rosella is one of the hibiscus plants and has great fruit that can be made into jams, wine, and tea.

That is just a few of the uses. But we found that the fish loved the leaves when the fish were 1-1 years old.

We believe the fish would continue to take the leaves as they age; however, this plant is a single-season variety, so it is a supplementary food.

We have a more robust rosella variety that has relatively narrow leaves compared to the leaves we fed the fish. Be aware of the variety if you wish to use this plant as food. Look for the large leaves.

rosella plant grown for fish food.
Rosella in the background. Flowers can also be fed to the fish.

Grass clippings.

We have a clean block, meaning we don’t use chemicals on anything in the yard. This allows us to find other uses for the stuff people usually chuck in the rubbish.

We tried grass clippings with the fish and had success with them. It was more a trial to see if they would take them than to find a substitution for the regular diet of the fish.

The good thing about the grass clippings is the fish left no trace, so you could throw them on the surface and walk away.

I would be wary of feeding your fish grass clippings if there are poisons used around your area. Fish a very sensitive so take care and think before acting.

Kang Kong.

This plant is a water cabbage and can be very aggressive in growth habits. We had it growing on the pool edge in grow beds, and we all ate from the plant.

The fish picked at the overhanging leaves while we picked the best leaves for the table. It was a win-win. It was grown by the fish in true aquaponics style. It’s a tropical plant, so check your area to see if it can grow.

grow beds growing food for fish and people
Kang Kong in the background. Image cut from video. Taro is the large leaf in front.

Katuk, aka Sweetleaf.

Sauropus androgynus

This is our staple leaf green for the whole family. We eat it. The chickens eat it, and the fish ate it.

If you are in a sub-tropical and warmer zone, it will be worth your while to investigate this plant. It is very high in plant-based protein, high in minerals, and is soft and full of flavor.

The fish ate this every day for most of their lives, and some were even caught by a hook with a leaf as bait., The plant grows profusely in the wet season and will easily spread from seed if you want to establish new thickets for food.

The seed pods of the katuk form pea like balls and have a nutty pea sort of flavor and although the fish never took to them, we did and still do.

With this plant, if we were not around for a day or so, we would cut a whole plant and tie it off at the side of the pool and let it hang in the water.

It would submerge and be pounded by the Jade Perch. It is a fantastic fish food and something that should be looked at further.

It is so useful as a fish food that I have often pondered about a fish pellet business based around the katuk with added rolled oats as a filler. Maybe one day, but our days are full, and time is short.

Feel free to take the idea and run with it. Get in touch, and I will be happy to give my thoughts.

You might have noticed I mentioned rolled oats above and that it’s not on the list. This is because we cannot grow the oats here, but we did feed the fish a handful each evening with the katuk leaves.

The plants on the list are what we know the jade perch will take without a problem.

katuk plant grown for fish food.
Sweetleaf/katuk in abundance. Jade perch LOVE this stuff.

Details to be aware of.

If you decide to feed the fish any of the items above, take note of where the food comes from. If you cannot grow it and do not know where or how it was grown, give it a miss.

In this “modern” way of living, it is accepted by society that poisons and toxins are fine on our food, and this might be ok with you as well.

But please note that fish are susceptible to toxins, and the simple spray residue on a store-bought mango that is over-ripe could kill fish.

Think on it.

As an example of how sensitive fish are to toxins, you can read a post about our pool system and cane toads killing small fish and then the jades eating the dying smaller fish.

This is from the smaller fish eating cane toad eggs. That article here.

Conclusions.

If you are looking at getting into or already are involved in aquaponics, you would most likely be aware of the growing crisis in our oceans and the troubling signs for the future of fish stocks.

We grew fish in the pool for our food purposes, but the fish species was chosen for the herbivorous attributes of the Jade perch. It will eat insects and smaller fish at times but prefers vegetation.

It is far easier to grow plant-based food here, so that was the reason. Your situation will be different, so do the research and don’t be afraid to experiment. Try new foods in small doses and monitor the tank. It is all part of the fun.

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