Do Fish Affect Other Members of the Food Chain?

Monroe Elementary School
Teacher: Annemari Goldsmith
Scientist:  Dr. Allen Hurlbert

A food chain shows which species eat which other species. Because all members of a food chain are directly or indirectly linked, we expect that the presence of one species can affect the number of other species in the food chain.

Hypothesis:

Does the presence of fish affect other members of the food chain?

Predictions:

We expect that ponds with fish have fewer brine shrimp compared to ponds without fish. We expect ponds with fish to have more algae than ponds without fish.

Materials:

8 mosquito fish
pond water with algae
brine shrimp [sea monkeys]
8 small tanks
8 plastic eye-droppers
4 funnels
filter paper
water bottles for filtration

Methods:

We created 8 experimental ponds by filling 8 tanks with pond water containing algae. We used filter paper to measure how much algae was in the water.
We added a dropper full of brine shrimp to each tank. We counted the number of brine shrimp in each tank. Then we added 2 mosquito fish to 4 of the tanks; the other 4 tanks remained without fish.

Results:

The fish ate all the brine shrimp quickly so that there were none left after the first day. The difference in algae was smaller than the difference in brine shrimp.

Conclusions:

Our first hypothesis was supported because brine shrimp decreased as soon as fish were added. However, some unknown conditions in the water killed the brine shrimp, even when fish weren't present. W conclude that fish can definitely affect brine shrimp populations, but we would have to try another experiment to
conclude whether fish could also have an effect on algae.