Purpose: The purpose of this experiment is for students to gain experience in altering the dissolved oxygen content of  water and to observe how goldfish respond to different oxygen levels in their environment.

• 3 goldfish 
• 3 - 1000mL beakers (Pyrex or other heat treated glass)
• 1-Thermometer
• 1-Large plastic tub (~ 30 cm long, 30 cm wide, and 15 cm deep)
• 1- Electric aquarium air bubbler
• Dissolved oxygen measuring kit
• Marker and masking tape

Note: Read all of the instructions before proceeding!!

1. Fill all three of the beakers with 750 mL (milliliters) of water from the aquarium that contains the goldfish. 

2. With masking tape and a marker, label one beaker "High Dissolved Oxygen", one beaker "Low Dissolved Oxygen", and the third "Control".

3. Fill the plastic tub with ice, until it is almost full. Then add water to it until the water is about two centimeters below the rim of the tub. This will serve as the water bath that will be used to cool the Low Dissolved Oxygen beaker in step 7.

4. Place the electric aquarium air bubbler in the beaker labeled High Dissolved Oxygen. Let it bubble for at least 10 minutes.

Note: Be sure not to remove the aquarium bubbler until immediately before you place the fish in the water.

5. Set the Control beaker aside. Use the thermometer to check the temperature of the water in this beaker. Be careful not to agitate the water; disturbing the water will increase the amount of dissolved oxygen in the water.

6. Heat the beaker that is labeled Low Dissolved Oxygen using a microwave, stove or hotplate. Heat the water until it boils and allow it to boil continuously for at least 5 minutes.  Be careful, boiling water can cause severe burns.

7. After boiling the water, carefully place the beaker (Low Dissolved Oxygen) containing the heated water into the plastic container that is filled with ice water.  

8. Place a thermometer in the water (Low Dissolved Oxygen) and immediately cover the beaker with plastic wrap.  Carefully push the plastic wrap down inside the beaker.  Avoid burning yourself during this procedure by using a blunt instrument to position the plastic wrap such that there is no air space between the water and plastic wrap. Remove the beaker (Low Dissolved Oxygen) from the ice-water bath when the temperature of the water has dropped to approximately the same as the temperature as the water in the control beaker ~24-26 ºC.

Note:  Make sure you stir the water gently to get an accurate measurement of the temperature.  Stirring the water very gently will help to distribute the temperature evenly throughout the solution. If you stir the water too briskly, you will reintroduce oxygen into the water.

9. Using the measurement kit, measure the dissolved oxygen of the water in each beaker.

Note:  Be sure to carefully follow the directions included with the water quality kit.

10. Make predictions on the behavior of each goldfish in the three different dissolved oxygen environments. Record your predictions in the Student Journal Activity.

 

 

Observations:

11. Remove 3 goldfish from the aquarium and place one goldfish into each of the three beakers.

Note:  While doing this, try to avoid agitating the water.  Keep the plastic wrap over the Low Dissolved Oxygen beaker at all times.  Make sure that the air bubbler in the High Dissolved Oxygen beaker is removed.

12. Allow the fish to be undisturbed for 5 minutes to acclimate to the different environments.

13. Pick one of the following physical movements to monitor in every goldfish:

• swishing of tail
• flexing of mouth
• flexing of gills

Each of these movements are normally performed by fish.

14. After the  5 minute acclimation time has passed, make observations on the behavior of your fish.  

      Count the number of times the goldfish makes the selected movement during a 1 minute observation period.

 

      Record your observations in the Student Journal Activity sheet.

                Note: Counting the number of times that fish swishes their tails is probably the easiest measurement to make

14. Compare your results with what you predicted.  Are the results what you expected? Are the behaviors of the fish in the experimental groups different from the fish in the control group?