Science Buddies: "Ask an Expert"

im trying to do an experiment testing the effect of caffeine on goldfish. how should i test this? some people have said to count their gill movements but others have said that is not a very valid method. how should i test this?

Hello,

Your experiment sounds very interesting and is very applicable- coffee is often dumped down the drain, and ends up in the sewer and this caffeine eventually makes it into fishes’ environment. One way to test the effect of caffeine on goldfish is to measure their heart rate. One would expect caffeine to increase the heart rate of goldfish, since caffeine increases blood flow; you can adapt your hypothesis around this. Measuring their heart rate can be done indirectly by measuring their respiration rates. Since oxygen is consumed during respiration, you can use the oxygen consumption rate as an indicator of respiration rate. To measure the oxygen consumption rate, you can use a dissolved oxygen kit (they are found on Amazon) to measure the amounts of dissolved oxygen before and after the fish are in the tank. For this experiment, you should include a control group- the fish that are not given the caffeine to compare their rates of respiration with the fish given the caffeine. Also, there are many variables you will need to control in this experiment, such as the amount of oxygen in the fish tank before the experiment, the size of the fish tank, light exposure and the health of the fishes.

Hope this helps!
C.M.

hey do you know how many milligrams it will take to affect the goldfish but not enough to kill them?

Hello,

Based on the data from other studies on goldfish, I would say anything above 10mg of caffeine is typically lethal to goldfish.

Here is one study with very clear data/experimental procedure: http://www.mybehaviorscience.com/sites/ ... eFINAL.pdf

Just as a side thought, another way you could extend your experiment is to compare the amount of caffeine different species of fish can intake without dying. This would allow you to see which fish species will be the most affected by the presence of caffeine in the ocean.

Good luck!
C.M.