EVERYDAY SCIENCE

Detailed explanation-1: -Some fish species can live in both freshwater and saltwater. These species are called euryhaline fish. However, most fish species can only survive in one or the other based on their salinity tolerance, or how much salt their bodies can handle.

Detailed explanation-2: -The action of osmosis can be very harmful to organisms, especially ones without cell walls. For example, if a saltwater fish (whose cells are isotonic with seawater), is placed in freshwater, its cells will take on excess water, lyse, and the fish will die.

Detailed explanation-3: -Freshwater fish maintain the physiological mechanisms that permit them to concentrate salts within their bodies in a salt-deficient environment; marine fish, on the other hand, excrete excess salts in a hypertonic environment. Fish that live in both environments retain both mechanisms.

Detailed explanation-4: -If you plopped a marine fish in fresh water, it would start absorbing lots of water across its gills. It wouldn’t take long for it to get into trouble with the balance of water and salt in its body. It might even swell up! This is because their bodies are more salty than fresh water, so they absorb water via osmosis.