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Good observation, Mr. Fischer. Also, in thermally polluted waters, warmer temperatures increase the metabolism of fish, so they eat more aquatic insects. At first a fish population grows, but eventually the food source is depleted, and there are problems in the food chain.

The Firehole River may provide us with a glimpse of how a naturally thermally influenced ecosystem has adapted over an extended period of time. While human caused thermal pollution may have begun a little over 100 years ago, Yellowstone's waters have been thermally influenced for tens of thousands of years. The waters of Yellowstone may provide a window into the future... a way to perhaps predict what might happen in other areas over time. We've observed that trout have changed some important life functions in the heated versus the unheated portions of the river. Those in the unheated areas feed on immature, bottom-dwelling insects—such as caddisfly larvae—while in the warmer parts of the river, they gulp down mollusks, true flies and mayflies, and feed mainly on winged insects, rather than on larvae. The warm-area browns have two annual growth periods and are much longer. Those from the cooler sections have only one annual growth period and are smaller. Mr. Fischer, did your group notice anything special about the rainbow trout?

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Cast of characters - Maya Crowbes, Dr. A Beadle, Gray Fischer, Viola DeRama
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Q: How is the life history of brown trout different in the heated parts of the river?

GLOSSARY: metabolism—the physical and chemical processes in which food is converted by an organism for the maintenance of life

deplete(d)—to exhaust the supply of something

mollusk(s)—an invertebrate typically having a hard shell that encloses a soft body, such as a snail or bivalve