PURPOSE:  To demonstrate the effect of decreasing temperature on the visible activities of a goldfish.

MATERIALS (per group):  600 ml container with goldfish in aquarium water; culture dish or other shallow container, crushed ice or snow, thermometer, clock with a second hand.

INTRODUCTION:  Northern animals have evolved various ways to cope with cold winter weather.  Some species hibernate, and some species migrate.  Northern animals that "stay and take it" have special adaptations that help them survive the winter.  Warm-blooded animals (homeotherms) may increase their metabolic rate to maintain body temperature in the cold. Cold-blooded animals (ectotherms) lack this heat-regulating mechanism.  Their body temperatures and metabolic rates change with environmental temperatures. 

In this activity you will use crushed ice or snow to gradually lower the temperature of the water surrounding a goldfish.  You will count the number of gill cover beats or mouth movements as a measure of the metabolic activity of fish in the cold.

PREDICTION: Use what you know about fish, metabolic rate, and temperature to make a prediction.

1. Will the metabolic activity of the goldfish increase, decrease, or stay constant as the water becomes colder?

PROCEDURE:

A.  Your teacher will give you a goldfish in a container.  Measure the temperature of the water in ^oC and record it on your data sheet.  Keep the thermometer in the beaker.

B. Back away, avoid sudden movements, and wait until the goldfish is stationary or swimming slowly.  Count the number of gill cover beats or mouth movements for exactly 30 seconds.  Record this number, and multiply it by 2 to get the rate in beats/minute.

C. Carefully put the beaker with the goldfish in a shallow container of ice water.  Record the time on the data table.  After 2 minutes, lightly stir the water without touching the fish.  After another 3 minutes, measure the water temperature and count the number of gill cover beats or mouth movements for 30 seconds. Record your data and calculate the gill cover rate in beats/minute.

D.  Use the same method to obtain the number of gill cover beats/minute at 5 minute intervals until the temperature drops a maximum of 10^oC.  A decrease in temperature of 10^oC over 20 minutes will not stress the goldfish.

E. Construct a graph of your data with temperature on the horizontal axis and number of gill cover beats/minute on the vertical axis.

DATA:

CONCLUSIONS:

2. According to your graph, what is the relationship between temperature and the number of gill cover beats per minute in goldfish?

3. What is the relationship between the number of gill cover beats/minute and the rate of metabolism in goldfish?

4. How do your results compare to your prediction?

DISCUSSION:

5. Find out what the word "torpor" means by looking it up in a dictionary.  Did your goldfish go into torpor?  What is your evidence?

6. Do you think that observation of swimming behavior would provide better evidence than gill cover beats for determining torpor in goldfish?  Why or why not?

7. Do you think fish require more food or less food when water temperatures become colder during winter?  Explain your ideas.

8. Besides fish, what other kinds of vertebrates are ectotherms?  If these animals were exposed to decreasing temperatures, what activity could you measure to indicate torpor?

9. In a large lake in winter, where do you think you would find more fish -- right under the ice or in deep water?  Explain your ideas.

OPTIONAL DISCUSSION QUESTION:

10. Some ice-covered lakes and ponds show evidence of winterkill, even though the water temperature is not lethal to fish.  Suggest one possible reason for the death of the fish.