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in higher latitudes where lakes freeze over in winter, how do cool fall temperatures fish make it through the winter?

the cooling water slows fish metabolisms down and allows them to go into hibernation in winter.
water from the bottom of the lake raises and provides oxygen to the cooler waters on the surface.
cool water at the surface traps nutrients deep in the lake to provide food during the winter.
the water in contact with the air sinks and mixes with the less oxygenated water in the deeper levels.

Cool water at the surface traps nutrients deep in the lake to provide food during the winter.

Explanation:

During winter, ice forms on the surface of the lake when the temperature drops below 4 degrees Celsius. However, the water below remains warm because the ice layer on top also acts as insulation of heat transfer in case of further temperature drops. Further, ice formation retains/seals off nutrients and gases flow below the ice sheet. The amount of nutrients is sufficient for phytoplankton activity during light hours (there is no complete darkness even after thick ice sheet is formed). Resultantly, the photosynthesis produces oxygen and food for aquatic organsism within the lake environment and support their survival during winter season.

explanation:

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