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