Water Quality - Unit 5

Nitrates

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

Materials:

    • 3 goldfish 
    • 3 - 1000 mL beakers
    • Marker and masking tape
    • Nitrate nitrogen measurement kit
    • Dissolved oxygen measurement kit

Note: Read all of the instructions before proceeding!!

General Setup:

1. Fill all three of the beakers with water taken from the aquarium that the goldfish are in. Fill each beaker with 1000 mL (milliliters) of water.

2. With masking tape and a marker, label one beaker High Nitrates which will represent a high level of excess nitrates in the water. Label a second beaker Low Nitrates, which will represent a low level of excess nitrates in the water and the third beaker, label Control; this will represent approximately normal conditions.

Preparation of the Beakers:

3. Set the Control beaker aside.  No fertilizer pellets should be added to this beaker.

4. Add an amount of fertilizer pellets that will yield 2 parts per million of total nitrate nitrogen to the beaker that is labeled Low NitratesIf you are not sure how much fertilizer to add, ask your teacher for help with this step.

5. Add an amount of fertilizer pellets that will yield 10 parts per million of nitrate nitrogen to the beaker that is labeled High Nitrates.  If you are not sure how much fertilizer to add, ask your teacher for help with this step.

It will be necessary to use the a laboratory scale to determine how many of the fertilizer pellets (mass) to add to the beakers to make solutions with 2 and 10 parts per million of nitrate nitrogen.

Determination of Nitrate Nitrogen Level:

6. Determine the nitrate nitrogen concentration of each beaker. To do this, use the nitrate nitrogen test kit from the Water Quality test kit and follow the directions carefully.  The test kit will yield a measurement in parts per million (milligrams of nitrate nitrogen / 1000 mL of water).

Predictions:

7. Make predictions on the behavior of each goldfish in the three different nitrate nitrogen level solutions. Record these predictions in the Student Journal Activity.
                Wait ~ 3 weeks before introducing the fish into these beakers.
Observations:

8. Take three of the goldfish currently in the aquarium (each group takes three fish), and place one in each of the beakers.

9. Allow the fish to be undisturbed for 5 minutes in each beaker. This period allows the fish time to acclimate to their new environment. Be sure to note the time when the fish are placed into the beakers.

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

    • swishing of tail
    • opening/closing of mouth
    • flexing of gills
Each of these movements are done by the goldfish at a measurable rate in a normal environment. 

Note: It has been found that counting the number of times that the fish swishes its tail is probably the easiest measurement to make.

10. After 5 minutes have elapsed, make observations on the behavior of the fish.

      Count the number of times each goldfish makes the selected movement during a 1 minute observation period.  Also, record any differences in the speed that the fish move, their physical appearance, or their general behavior.

Record your observations in the Student Journal Activity sheet.
                  

Discussion:

11. Compare your results with what you predicted.  The results will be based on measurements of either swishing of the tail, opening/closing of the mouth, or flexing of the gills.  Are the results the same as the predictions or are the results different?  Is the general behavior different or the physical appearance of the experimental fish different from the control group?