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Fish in Lakes

Fish in Lakes. Lake Food Chain. Generally represent the end of the food chain in most lakes Only a small fraction of the energy fixed in the system makes it to this level. Lake Food Chain. Important group because of effects they can have on all other levels of living things in lakes.

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Fish in Lakes

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  1. Fish in Lakes

  2. Lake Food Chain • Generally represent the end of the food chain in most lakes • Only a small fraction of the energy fixed in the system makes it to this level

  3. Lake Food Chain • Important group because of effects they can have on all other levels of living things in lakes

  4. Feeding Categories • Piscivores - feed on fish • Basses, pikes, walleye

  5. Feeding Categories • Planktivores - feed on phytoplankton, zooplankton • Visual particulate feeders or strainers • Young of many species, clupeids like alewife

  6. Feeding Categories • Benthivores - pick materials off bottom • Macroinvertebrates, algae, plants, detritus • Suckers

  7. Feeding Categories • Omnivores - feed on everything • Carp, gizzard shad (planktivore tendencies)

  8. Trophic Control • Each trophic group is important, but piscivores & omnivores have more overall control on the entire system

  9. Trophic Control • Strong populations of piscivores can keep other fish types in check and keep system “balanced” • Top-down control

  10. Out of Control! • In absence of predators, other fish types can dominate, affect other lake components • Planktivores - shad • Benthivores - stunted bluegill

  11. The Carp Cascade • Feeding activities of carp can modify littoral substrate and muddy the water • Macrophytes cannot grow • Muddy water - reduced transparency, reduced phytoplankton, reduced zooplankton, etc.

  12. The Bottom Line • Presence or absence of a single species may have significant impact on the functioning of the entire lake

  13. Fish Productivity • Varies greatly among different fishes • Fishes feeding nearer the base of the food chain (herbivores) are more productive than predatory forms

  14. Fish Productivity • The younger the fish population (mean age), the more productive it is • Young fish, greater % of food intake to growth • Older fish, greater % of food intake to maintenance

  15. Fish Productivity • In temperate zone lakes, production of fish limited mostly to spring, summer, autumn • Considerably lower than in tropical lakes

  16. Fish Productivity • Tropics: 100s of g/m2/year • Temperate lakes: 1-20 g/m2/year • Temperate streams: ~50 g/m2/year

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