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ACTIVITY: Aquaponics in a Bottle

NGSS Science and Engineering Practices:

NGSS Crosscutting Concepts:

NGSS Disciplinary Core Ideas:

The activity below draws from the content in the page Ecosystem Cycling.

Phenomenon:

<p><b>Fig 1.</b> Parrotfish help cycle matter by expelling fine-grain coral sand on a tropical reef at Palmyra Atoll. Palmyra Atoll is in the center of the Pacific ocean basin.</p>Animals take in matter when they eat and lose matter when they poop (Fig. 1).

Inquiry:

How does matter cycle through the ecosystem?

Guiding Questions:

  1. Where to plants get the energy needed to survive?
  2. Where do animals get the energy they need to survive?
  3. What happens to the materials that animals eat?

Activity:

Create your own mini aquaponic system in a bottle and observe the relationships between organisms. 

If you haven't already played the aquatic food chains game, check it out on the bottom of the page Ecosystem Cycling!

Note to teachers:

This ecosystem-in-a-bottle is a simple example using recycled 2L bottles, but it can be adapted to make it bigger or more complex. To connect the hydroponics activity to this one, click the further Investigation below to set up your system in a two part series. You will first establish a hydroponic system in a larger tank. This will allow you to then add fish to the system to create a more complete and cycling ecosystem.



Materials:

  • Two, clear two-liter soda bottles (another transparent plastic container may be substituted)
  • Scissors
  • Gravel
  • Water
  • Guppies (or other small fish)
  • Algae-eating fish or snails
  • Fish food (can be purchased from a pet store)
  • Elodea plants (also called anacharis and can be purchased at pet stores) or other aquatic plants, such as duckweed
  • Gravel
  • Soil
  • Small plant or seeds (herbs like basil grow easily)
  • Drill with small drill bit (or alternative tool sharp enough to poke small holes in bottle cap)
  • Optional:
    a. Aquarium aerator, with tubing and airstone. You can purchase splitters so multiple tubes with airstones can be divied to separate aquaria.
    b. Turkey baster for ease of water changes.

Recommendations:
  • If possible, take students on a field trip to collect organisms like small fishes, snails, and aquatic plants from nearby streams. You will need at least one small fish per bottle. If you cannot collect enough organisms for the entire class, you can purchase small fishes and aquatic plants from a pet store. 
  • Allow the water to sit out for at least 24 hours so the chlorine in the tap water evaporates (or use commercially available drops to treat the water).
  • Do not put the bottle aquarium in direct sunlight as it will overheat the water and increase algal growth.
  • Pre-rinse the gravel so that there is no mud or sand.  You will need enough gravel to fill the bottom of the bottles and hold the Elodea plants in place.
  • If the top portion of the bottle doesn’t sit at the right height, you can use wooden skewers as support beams. Poke two holes all the way through the top portion of the bottle and place wooden skewers through them. Allow them to protrude about an inch on each side. These will allow the planted section to sit higher above the aquarium.

 

Important Note to the Teacher:

Invasive species concerns: It is important to dispose of organisms (plants, fish, snails, etc) properly so that native habitats are not harmed. Return organisms to the place wher you caught them, but do not release organisms bought from the pet store into the natural environment. The release of pet store guppies is likely the reason for their presence in Hawaiian streams and their negative impact on native species: https://dlnr.hawaii.gov/ais/other-ais/guppies/.

Please see http://www.habitattitude.net/ for guidance on aquarium disposal.

Care of living organisms: This activity involves observation and experimentation with small fish, which are vertebrates. Consideration of proper, humane care of vertebrates is important.  Provide explicit guidance for students to develop an understanding of and value for life and living organisms. The guppies must be provided with appropriate daily care so that they remain healthy during the course of the experiment and should not be subjected to pain or discomfort.

Students need to be supervised by a teacher that understands the safe and responsible use of animals in the classroom and who understands and follows Hawai‘i Department of Education policies and other relevant regulations. Teachers must develop and implement a plan for the future care of the fish and other organisms following the study.

(Adapted from the National Science Teacher Association’s 2005 Position Paper: “Responsible Use of Live Animals and Dissection in the Science Classroom”)

Proper care of small fish, like guppies includes:

1. Feeding them daily, i.e. making sure there is a source of food such as elodea, or providing fish food flakes.
2. The temperature of the water must be between 72° and 82° F.,
3. Change approximately 1/3 of the water every 1 to 2 weeks, or as needed to keep the water in good condition.
4. Create a happy or natural environment by adding things like gravel and plants to the tank. Care of the guppies must be provided daily, including weekends, holidays, and other times school is not in session. When the experiment is over you must continue care of the guppies in the classroom or implement another plan for the continued proper care of the guppies, as they cannot be re-introduced into Hawai‘i’s environment.

For further information regarding current policies and regulations in Hawai‘i contact the Science Section of the Instructional Services Branch of the Office of Curriculum, Instruction, and Student Support at the Hawai‘i Department of Education.

Procedure:

  1. Follow along on your worksheet to build an aquaponics system in a bottle!
  2. Before building your aquaponics model, think about these questions and answer them on your worksheet:
    1. How do scientists study plants and animals in their natural habitats?
    2. What might be some limitations, challenges or risks with studies in the natural environment?
    3. How are models beneficial to scientists when studying plants and animals?
    4. What is the ethical treatment of living things? How will you ensure your animals are being treated ethically?
    5. Why do animals, including humans, eat things?
    6. Do plants eat?
    7. What is a producer? Consumer? Decomposer?


Collect your organisms:

  1. Collect organisms from a local stream if you have permission and safe, easy access.
    1. Organisms may include guppies, snails, shrimp, and freshwater plants such as elodea and duckweed, etc.
    2. Keep in mind the aquarium will be very small, so you don’t want to overcrowd them!
    3. If you don’t have access or permission to a local stream, organisms can be purchased from a pet shop.
  2. Prepare water by allowing it to sit out over 24-hours so the chlorine can evaporate (or use commercial drops).

Build your aquarium:

  1. Rinse each two-liter soda bottle with clear water to get rid of any residue. Do not use soap!
  2. Cut off the bottle top at the shoulder above where the bottle tapers – i.e. cut it so the lower aquarium portion will have a bit of curvature at the top (see figre). Save the top half to be used later!
  3. Rinse the gravel and add a layer to cover the bottom.
  4. Place roots of elodea or other aquatic plant within the gravel.
  5. Fill the bottle with prepared water leaving an inch and a half of space at the top.
  6. Add snails and 1 or 2 guppies and/or shrimp.
  7. Add a small portion of floating plant, like duckweed, to the surface of the water. Don't cover the entire surface, or the oxygen can become depleted!
  8. You may add other small plants or creatures that you think would be a good fit for the ecosystem. Keep in mind this is a very small aquarium, so don't add too much.
  9. If you have an aerator, position your aquarium near a plug and plug in the aerator. Place the airstone within the ecosystem.

Plant your seeds!

  1. Remove the bottle cap from the top portion that you cut off of your original bottle and poke 10-15 holes in it.
  2. Screw the bottle cap back on. Flip the top over and add a small amount of gravel to the bottom – enough to fill just above the bottle cap line.
  3. Fill the remainder of the top with soil.
  4. Plant your seed or small plant in the soil.
  5. Place this newly created mini garden on top of your bottle aquarium so that the cap is slightly submerged in the water below.
  6. If the bottle top doesn't rest on the brim of your aquarium, you can use wooden skewers as support beams.
    1. Poke two holes on opposite sides of the bottle top and slide wooden skewers through them. Allow them to protrude about an inch on each side. Do this on both sides (Fig.3).

Care for your ecosystem!

Note: Your system should be able to maintain itself through the cycling of matter between producers, consumers and decomposers. However, since this system is small, it is helpful to supplement the trophic levels to ensure they are getting enough energy.

  1. FEEDING: Drop a few flakes or pellets (depending on food choice) on the surface of the water to feed the fish every other day (every 2 days should also be fine).
  2. WATERING: Water your seed/plant at the same time as fish feeding.
  3. CLEANING: You will need to replace (especially if you do not have an aerator) about 1/3 of the water every 1-2 weeks as needed. This will prevent algae buildup and ensure enough oxygen is available (The plants will contribute to the oxygen available).
    a. Prepare replacement water the day before, allowing it to sit out over night to evaporate any chlorine.
    b. Remove the top (plant or cap) and scoop out about 1/3 of the water using a cup (a turkey baster can also provide easy access to removing water).
    c. If there is algae build up on the exposed walls, you can wipe it off with a paper towel or clean sponge to prevent overgrowth.
    d. Pour in fresh water so as not to stir up any loose particles.

Observe your ecosystem!

  1. Now that you have built your ecosystem, think about the original questions we posed and make observations over time. 
Recorder Time/Date What we observed
     
     

Activity Questions:

  1. Draw your own food web based on your ecosystem in a bottle (there are many correct food webs!).
  2. What roles do plants play in an ecosystem?
  3. How are animals important to the food web?
  4. What are the trophic levels represented in your ecosystem in a bottle?
  5. Which organisms are primary producers? Consumer?
  6. Where are the decomposers in your aquarium?
  7. Do all of the organisms in your aquarium have the food that they need to survive?
  8. What might happen if a top predator was introduced, such as a crayfish, goldfish, or African frog?
  9. Is there evidence of any other plant life in the aquarium? (Hint: It is possible that microscopic freshwater algae may have formed as well, and if it becomes dense enough may appear either as a greenish film, or perhaps a greenish hue in the water.)
Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawaii, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.