* Freshwater is hypotonic: This means it has a lower concentration of dissolved salts than the animal's body fluids.
* Water movement: As a result, water constantly moves into the animal's body through osmosis (diffusion of water across a semi-permeable membrane from a high concentration to a low concentration).
To survive, freshwater animals have evolved adaptations to deal with this constant influx of water:
* Excretion of dilute urine: They produce large volumes of dilute urine to get rid of excess water.
* Limited drinking: They drink very little water, as they are constantly absorbing water from their surroundings.
* Active salt uptake: They have special mechanisms to actively absorb salts from their environment, usually through their gills or skin.
Other adaptations:
* Streamlined body shape: This helps fish move efficiently in the water.
* Strong fins and tails: These help fish maneuver in the water currents.
* Camouflage: Helps them avoid predators and ambush prey.
* Special respiratory systems: Many freshwater animals have evolved gills to extract oxygen from the water.
Understanding these adaptations is crucial for understanding the success of freshwater ecosystems and the challenges faced by the animals living in them.
