Limiting Factors on Fish Populations

A composite of photos showing insects that certain fish like to eat. Photos include a mayfly (left), a dragonfly (middle), and a stonefly (right).
A composite of photographs showing various insects that trout and other fish eat.  The photos include a mayfly (left), a dragonfly (middle), and a stonefly (right).

National Park Service Photos


You’re Correct!

Although most streams in the park are very clear, cold, and pollution free, they are not very productive in terms of growing big trout. Most rainbow and brook trout in the park grow relatively fast, live only about 3 years, and die due to a lack of food resources. The diversity of aquatic insects in park streams is quite high, but the density of each species is fairly low making food resources for competing trout scarce. However…

A composite of photos displaying various food items for larger fish such as brown trout.
A composite of photos showing various food sources used by larger growing fish such as brown trout. The photos include (from left to right)a crayfish, a warpaint shiner, a frog, and a salamander. 

The exception to this rule in the Great Smoky Mountains National Park is brown trout. Brown trout, when around eight inches in size, expand their menu to include a diet high in fish, crayfish, frogs, and even salamanders. Brown trout still forage on insects, but these additional protein sources enable them to attain much larger sizes than the brook and rainbow trout.

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Last updated: April 14, 2015

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