A Fishy Tale
The movement of blood cells through blood vessels is hard to observe in humans, but can be seen
clearly in the tail of a goldfish. In this investigation, you will observe the normal flow of blood through
capillaries, arteries, and veins of a fish. You will then observe the effects of nicotine, alcohol, and
caffeine on the blood vessels and blood flow.
Materials: petri dish, absorbent cotton, dropping pipette, microscope, beaker of water, goldfish,
colored pencils
Procedure:
1. Read through the entire procedure before starting. Tear a thick piece of cotton slightly larger
than needed to wrap around the goldfish and stretch out so it is thin. Soak the cotton in fish
tank water and place the wet cotton in the petri dish.
2. Gently place a goldfish in the petri dish and wrap the cotton over the fish so that it’s gills are
covered with the wet cotton but not its tail.
3. Add a small amount of water to the cotton every few minutes with a pipette so that your
goldfish does not dry out. Only keep your fish out of the fish tank for a few minutes. If the
circulation stops, remove the fish from the cotton and put back in the fish tank. You may need
to push the fish through the water once or twice to apply artificial respiration. When handling
or touching the fish, always use the wet cotton or a net and do not touch the skin of the fish
with your fingers.
4. Wipe the bottom of the petri dish dry and lace the petri dish with the wrapped fish on the
microscope stage. Focus the low power on the tail and move the dish around until you locate
a part of the tail in which you can observe blood vessels clearly. The red bodies you see are
the masses of pigment in the fish. Near the posterior edge of the tail the pigment thins out and
you can see blood vigorously flowing through vessels. Concentrate your observations in this
region.
5. Locate the arteries, veins, and capillaries. Sketch with color a portion of the tail in the space
below. Label an artery, vein, and capillary.
6. Compare the walls of the three types of blood vessels. Record your observations.
7. Compare the rate and method of blood flow in the three types of blood vessels. Record your
observations.
8. For a period of 2-3 minutes, carefully observe the blood cells in a group of capillaries.
Compare the diameters of the capillaries and the red blood cells. Does each capillary function
continuously? Explain. Does blood always flow in the same direction through a particular
capillary, or does the flow change direction?
9. When you have finished with the fish, replace it in the fish tank to recover. If it does not revive
immediately, apply artificial respiration by slowing moving the fish around in the water.
10. Prepare your petri dish and cotton as you did in step 1. Obtain another fish and prepare as
you did in step 2.
11. Add a drop of nicotine, alcohol, or caffeine solution (ONLY 1!) to the fish’s tail and observe the
arteries, veins, and capillaries. Sketch with color a portion of the tail in the space below. Label
an artery, vein, and capillary.
12. Compare the walls of the three types of blood vessels. Record your observations.
13. Compare the rate and method of blood flow in the three types of blood vessels. Record your
observations.
14. Return the fish to the tank for recovery.
15. Repeat steps 10 and 11, for each of the other solutions until you have observed the results of
all three solutions. Use a different solution as before!!!
16. Sketch with color a portion of the tail in the space below with solution #3. Label an artery, vein,
and capillary.
17. Compare the walls of the three types of blood vessels. Record your observations.
18. Compare the rate and method of blood flow in the three types of blood vessels. Record your
observations.
19. Return the fish to the tank for recovery.
20. Repeat steps 10 and 11, for each of the other solutions until you have observed the results of
all three solutions. Use a different solution as before!!!
21. Sketch with color a portion of the tail in the space below with solution #3. Label an artery, vein,
and capillary.
22. Compare the walls of the three types of blood vessels. Record your observations.
23. Compare the rate and method of blood flow in the three types of blood vessels. Record your
observations.
24. Return the fish to the tank for recovery.
Answer the following questions on a separate sheet of paper regarding the lab investigation.
Answer #25 through 29 with the fish under normal conditions.
25. Explain how you can quickly tell the difference between an artery and a vein in the fish tail.
26. Which type of vessel seemed to be more numerous in the tail of the fish? Explain why it is
essential that there be more vessels of this kind.
27. In your observation of the fish’s tail, which blood vessels does the blood move the slowest?
Why?
28. In your observation of the fish’s tail, in which blood vessels does the blood move fastest?
Why?
29. Describe another way that you could tell the difference between the arteries and veins in the
tail of the fish. (Hint: all the images that you see in the microscope are reversed!)
30. What is the effect of alcohol on the diameter of blood vessels?
31. What is the effect of nicotine on the diameter of blood vessels?
32. What is the effect of caffeine on the diameter of blood vessels?
33. How might nicotine affect the performance of athletes?
34. How would alcohol consumption affect persons exposed to cold weather?
35. How does the consumption of caffeine give you the feeling of “waking up”?
36. Under what natural conditions might capillary diameter change?
37. How might nicotine, alcohol, and caffeine in a pregnant mother’s system affect the blood
supply to a developing fetus?