Aquaponics + Trout in the Classroom

Introduction: Aquaponics + Trout in the Classroom

About: I'm a middle school science teacher going on 17 years in the classroom. I've taught 6th, 7th, and 8th graders. I'm constantly looking to improve my instruction and Instructables is one of the places I search…

Trout in the Classroom is a program that delivers trout eggs to schools (early in the academic year) so that students have the opportunity to learn things like food chains and food webs, pH, water pollution, needs of living things, biotic and abiotic factor in an ecosystem, genetics, sustainability, being a steward for the environment, micro and macro invertebrates, etc... by raising the trout with their classmates. Here is a link to the TIC program. If you go through the steps needed to obtain the trout, you might as well add to the learning experience by adding plants to teach about aquaponics.

*This set up could be used with many species of fish (you don't need trout). The more fish you have, the more nutrients you have to support plant growth.

The basic elements of an aquaponic system are light, plants, fish, and water. As long as the fish are well fed they will happily produce nitrogen to feed your plants and the plants will in turn thrive as long as they have plenty of water. The system can take care of itself as long as you feed the fish.

An aquaponic system is one that relies on Polyculture. This is a process by which one organism sustains another. In this case there may be multiple organisms but you get the idea. Aquaponics uses fish and other marine animals to produce waste that plants use for nutrients. Conventional fertilizer is made from decaying biological matter and wastes so by using live fish to produce waste you are eliminating the need for fertilizers. Fish also produce ammonia in their waste which is high in nitrogen, an element essential for plant nutrition and growth . The fish are also a crop in themselves and can be harvested and either sold or eaten depending on your preference.

Step 1: Gather Materials and Get Growing

seeds (we grow lettuce because it does well with the cooler temps produced by the chiller in our trout tank)

rock wool

hydroponic baskets (2 inch diameter)

Polystyrene Foam Board Insulation (.75" works well)

drill or drill press

2 inch hole saw

Ruler to help with spacing holes evenly

Scissors (for harvesting lettuce)

Step 2: Get Growing

1. Cut the foam board to the best dimensions to fit in your tank. Keep in mind that you will still need to feed the fish and perform regular maintenance on things beneath the water, so you don't want it to take up the entire surface area of the water. You will also need to remember that the plants will need some room above them.

2. After you drill holes into the foam board, insert your baskets.

3. Next, add your cubes of rock wool (one cube per basket) and set it into your fish tank. The foam board is very buoyant and will float high on the water.

4. Finally, add two or three seeds to each rock wool cube and let them grow. You will want to have the lights about an inch above the plants when they first start sprouting. Thin the plants if necessary.

Here are some images that were taken during the growing process. I don't know what has come as a bigger shock to me, the fact that kids don't understand how long it takes to grow something from seed or that they don't understand how long it takes a fish to grow! I'm happy to have had the chance to help them understand.

One of the coolest things occurred last year when I had aphids all over the lettuce plants. My students would pick the aphids off the lettuce with tweezers and drop them into the tank for the trout to eat. It was awesome to see the entire system come full circle. We also collected lady bugs from the garden outside to help take care of the aphids from above the water. We never could get the little buggers under control, but at least we didn't use insecticides!

Here is a link that can give you more information about aquaponics if you're interested.

Step 3: My Set Up

I have two 55 gallon tanks that are joined using a tank bridge (4" PVC). The tank bridge is full of water and the fish have the ability to swim from one tank to the other. A more interesting tank bridge would be made of clear acrylic or glass so that you could see the fish swimming between tanks, but my main goal was less about aesthetics and more about function. I only have one chiller (the most expensive part of the setup). I assumed that if the fish had more space and less competition it would result in a greater survival rate. So far so good. In order to have two tanks and one chiller I needed to split the return line from the chiller so that it would empty into both tanks. I also needed to bulk up the insulation around the outside of the tank to help extend the life of the chiller. Students were responsible for the entire build under close supervision. The two inch thick insulation is expensive so students needed to measure twice before making any cuts. There is a bio filter in the tank on the right and the pump that pulls water to the chiller is also in that tank. The tank on the left has a charcoal filter. Each tank has it's own air stone.

Step 4: Harvest the Lettuce and Fish

If you cut back the lettuce periodically, it will continue to grow and develop a strong root structure. With a large enough system, you can grow the fish so that they can also be eaten. Because these trout were loaned with the expectation that they would be released in the spring, we won't be consuming these lucky Rainbows.

I hope you have the opportunity to try this out. Please let me know if you have any questions or think I could do a better job of explaining anything. Thanks in advance for any feedback!

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    6 years ago

    I think this is great but I have one question, let's say I had this already set up and there was some sort of nuclear fallout or the government collapses, are there any plants I can grow to feed the fish so the system runs infinitely? Thanks!


    Reply 6 years ago

    That's a great question. There are a number of different kinds of fish that you can grow in an aquaponic setup. Trout do not eat plants and need cold, flowing water so they would not be the best choice. Many people farm talapia because you can supplement their diet with duck weed, they can survive in lower oxygen environments, and you can raise quite a few in a small space. You could look into raising black soldier fly larva as a food source for the fish as well. Thanks for looking!


    6 years ago on Introduction


    Wish I had teachers like you back in the days! I maybe would have also considered becoming a teacher, if I would´ve had only a glimpse of hope I could do projects like this one day ...

    Also I often thought about connecting two tanks via a tube aka the communicating vessels principle, but never really tried. Seems to work obviously. And the fish really "get it" and use it?

    Kudos anyway!

    Regards, Confu


    Reply 6 years ago on Introduction

    Thanks Confu! The fish use the tank bridge, but tend to swim only in one direction. I have to scoop a few from one tank into the other every few weeks. Maybe they prefer swimming into the current? I just wish the bridge was clear.
    Awesome job with the pico aquarium. Great instructable and best of luck in the contest!


    Reply 6 years ago on Introduction

    Thanks and good luck to you as well!

    Well, I thought a while about the "one way" tank bridge.
    I have different sorts of tetras and I observed that they actually seem to prefer swimming 'into' the current. Sadly even lost 2 or 3 over the years which "tryed to pull a Nemo" in my open tank and accidentally jumped out of it while doing so. But luckily I observed the last wanna-be-Nemo and was able to save him and take precautions.

    So here my suggestion(s):

    I assume you got the outlet of the filter/cooler in tank A and the inlet in tank B.

    Maybe add a second bridge and place a small powerhead in front of it to generate an opposite current from tank B to tank A. Athmospheric pressure should do the rest, so current in A -> B tube will be a little stronger then, but the fish might try to take the other route against the current and come back to tank B again and "maybe" populate both tanks almost evenly.

    Maybe this might work. If it doesn´t work out well, another option might be to place inlet and outlet of the filter/cooler in one tank and add powerheads to both tubes.

    Just ideas, have no opportunity to test them.

    See drawing.

    Regards :)

    fish bridge.jpg

    6 years ago on Introduction

    This is a great project! Thank you for sharing this.