Lesson guide · Lesson 17 · Grades 3–8 · 6 min

The bacteria you cannot see

Meet the tiny living things that turn fish waste into plant food, and find out where they live.

Open the lessonPrintable worksheet

Students will

  • Explain that bacteria are living things too small to see.
  • Name the wet surfaces where bacteria live in an aquaponics system.
  • Explain why growers avoid scrubbing gravel clean and keep chlorine out of the system.

New words

bacteria
Living things so tiny you need a microscope to see them.

Talk about it

Where else have you felt a slippery film on something wet? What might be living there?

Check questions and answers

  1. Where does the Recycling Crew live?

    • On wet surfaces, like gravel and roots (answer) Right. They cling in a thin, slimy layer on wet surfaces.
    • Floating in the air above the tank Not quite. They need water. Look at the wet stones and roots.
    • Inside the fish food Not quite. They live on the wet surfaces all through the system.

  2. What does the crew need from the water to do its work?

    • Air (answer) Right. They use the air in the water to change the waste.
    • Chlorine Not quite. Chlorine can harm the crew. Growers keep it out of the system.
    • Bright light Not quite. They don't need light. Sunlight can even harm a new crew.

  3. Why don't growers scrub every stone clean?

    • They would wash away the crew (answer) Right. The slimy layer is where the crew lives.
    • The stones would break Not quite. Stones are tough. Think about the slimy layer on them.
    • Clean stones make the water too warm Not quite. Clean stones don't change the warmth. The crew is the problem.

Sources

  • Somerville, C., Cohen, M., Pantanella, E., Stankus, A. and Lovatelli, A. Small-scale aquaponic food production: Integrated fish and plant farming. FAO Fisheries and Aquaculture Technical Paper No. 589. Food and Agriculture Organization of the United Nations, Rome, 2014.
  • Rakocy, J. E., Masser, M. P. and Losordo, T. M. Recirculating Aquaculture Tank Production Systems: Aquaponics, Integrating Fish and Plant Culture. SRAC Publication No. 454. Southern Regional Aquaculture Center, November 2006 revision.
  • Deer, C., Hu, B., Dunn, B. and Dusci, J. Nitrification and Maintenance in Media Bed Aquaponics. Fact sheet HLA-6729. Oklahoma Cooperative Extension Service, Oklahoma State University, October 2021.
  • McGee, M. and Cichra, C. Principles of Water Recirculation and Filtration in Aquaculture. FA-12. Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. First published October 1988, reviewed April 2000.
  • Hargreaves, J. A. and Tucker, C. S. Managing Ammonia in Fish Ponds. SRAC Publication No. 4603. Southern Regional Aquaculture Center, December 2004.
  • McCoy, G. A. Water quality: Briefing paper on periphyton. Quality of Water Branch Technical Memorandum No. 78.10. U.S. Geological Survey, Water Resources Division, June 22, 1978.
  • Center for Biofilm Engineering, Montana State University. Biofilm Basics.
  • MedlinePlus, U.S. National Library of Medicine. Bacterial Infections.
  • National Human Genome Research Institute. Talking Glossary of Genomic and Genetic Terms: Bacteria.
  • City of Sioux Falls Water Purification Plant. Chloramines and Fish.