Experiments & Project Ideas

Question: Are There Protozoa In My Pond—Or Fish Tank?

Summary: Protozoa are one-celled creatures that live in water or watery tissues. In a culture medium, they will be visible in about 24 hours, with the most variety of protozoa visible after about 3 days.

Materials Needed:

(Any of The Materials Highlighted in Blue are Clickable Links for Purchasing)

Pond Water or Water from a Fish Tank

1 Egg

Pipet            

Microscope, Compound, up to 400x  

Microscope slides and cover slips    

Protozoa Calming Solution (Methyl Cellulose)            

Project Procedure:

1. Hard boil an egg and grind a pinch (1/4 gram) of the yolk in a bowl with a small amount of water to form a paste. Add the paste to 1 liter of boiled pond or fish tank water and let stand for two days.
2. Use the pipet to place one or two drops of the water on a microscope slide. Cover with the cover slips.
3. Place on a microscope stand and examine the slide with your microscope starting at 40x. Most protozoa have little color and are difficult to see in bright light, so turn your microscope diaphragm to the lowest light setting. It will take patience to adjust the lighting and focus the microscope.
4. Initially you will see very tiny dots moving around on the slide. Some move very rapidly, others more slowly. You can slow them down for observation by adding a drop of methyl cellulose.
5. Once you find an area of protozoa activity on the slide, turn the magnification up to 100x or even 400x to see them better.
6. If no animals are visible, try again each following day. Many conditions, such as water hardness, temperature, and water acidity, can affect the growth and development rate of these organisms. Each succeeding day you will typically find more and different varieties of protozoa in your culture. Initially, smaller species will be prevalent. As the days pass larger species will appear. You will also see different algae forms appear. Certain species will be more common from the top of the cup and others from near the bottom. Gradually, food and water conditions will change, affecting the growth and development rates of the different protozoa.