Students count the number of gill cover beats in a goldfish as an indication of decreasing metabolic rate at low temperatures to demonstrate torpor.

TOPICS:  Animals, respiration, metabolism

LEVEL: Middle and high school

TIME:  1 class period

ADVANCE PREPARATION:  It is important that the goldfish should be transferred to individual 600 ml beakers containing aquarium water at least ONE DAY BEFORE the experiment to acclimate them to new surroundings. See note for step B .

MATERIALS: You may wish to substitute native minnows for goldfish in this experiment .

PREDICTION: In class discussion, encourage creative, logical, and critical thinking. We recommend that you introduce the following ideas if they are not suggested by students: Cold temperatures result in decreased oxygen consumption, metabolic rate and activity in cold-blooded animals.  A term used to describe reduced activity in an animal is torpor.  In general, fish are ectotherms that go into torpor under cold temperature conditions.  Reduced metabolic rates in fish are shown by decreased rates of such activities as swimming and gill cover movements .

STEP B: If the fish are too active, you may wish to enclose the setup with a cylinder of construction paper with observation slits .

STEP C: Have students record clock time (9:22, 9:27, 9:32 and so on) in 5 min intervals in the first column of the data table .

STEP E: Students may have difficulty drawing meaningful graphs.  In science, only the positive x and y coordinates are used in most graphs.  Students may need help in selecting appropriate scales and labels.  You can use this opportunity to illustrate the usefulness of mathematics skills to the interpretation of scientific data.

QUESTION 5 may require library work.  Questions 5-10 require higher-order thinking skills.  We recommend that you discuss these questions in class before having students write out their answers .

2. The number of gill cover beats decreases as the temperature decreases .

3. The number of gill cover beats is a visible indication of the rate of oxygen consumption which is dependent on metabolic rate .

4. Answers will vary .

5. Torpor is reduced activity in an animal in response to environmental factors.  Goldfish go into torpor when temperatures are reduced as evidenced by reduced gill cover beats and slower swimming .

6. Swimming behavior is probably not as good an indication of torpor since the fish is unavoidably disturbed during the experiment.  Also, gill cover beats indicates oxygen consumption which is directly related to the organism's metabolic rate .

7. Fish require less food when water temperatures become colder because their activity level and metabolic rate decreases .

8. Amphibians and reptiles are ectotherms.  In frogs, you could measure breathing rate by observing throat movements. In other amphibians or reptiles, such measurements would not be easily observed .

9. In some large lakes in winter, fish are more often found in deeper water because the water temperature is slightly warmer compared to shallow water.  (Water is more dense at 4^oC than 0^oC, so it sinks to the bottom.)  In other lakes, fish may congregate under the ice where oxygen is produced by photosynthetic aquatic plants and the temperature is colder, thus reducing metabolic rates and conserving energy .

10. Highly productive, shallow lakes are especially prone to winterkill due to reduced dissolved oxygen concentration.  Oxygen is consumed by the high rate of decomposition and respiration occurring all winter under the ice.  Ice cover reduces oxygen exchange between the air and water.  Snow cover reduces light penetration, thereby reducing oxygen replenishment by photosynthesis.

Figure 1. Sample Graph