salmon
saltwater has salt in it, freshwater does not.
I think marine aquariums are saltwater unlike freshwater that do not have saltwater
Salmon can thrive in both saltwater and freshwater environments because they have the ability to regulate the salt content in their bodies. This allows them to adapt to different environments and migrate between the two.
Maybe that saltwater animal can endure hard water and freshwater animals can't.
Certain freshwater fish can survive saltwater conditions; examples are black mollies, mono's and scats. All of these fish aren't truly freshwater or saltwater, they are Brackish. Brackish is between freshwater and saltwater, and so these fish are highly adaptable.
Fresh water.
anadromous fishes - live in ocean reproduce in freshwater or catadromous fishes - live in freshwater but reproduce in saltwater amphidromus fishes - move between fresh and saltwater for non-reproductive reasons
The same as in the ocean
Freshwater mussels live in rivers, while saltwater mussels live in oceans. Even though it is mussels, it differs a lot. Freshwater mussel and saltwater mussels hunt different things, because they live in different places.
saltwater will corrode the aluminum and metal from an engine more than freshwater will. Therefore engines used in saltwater need sacrificial anodes to be the vulnerable part, thus protecting the engine.
The fact that a saltwater ecosystem has salt in it. 'salt'water ecosystem
Freshwater salmon live in rivers and lakes, while saltwater salmon live in the ocean. Freshwater salmon have a more streamlined body shape and are typically smaller in size compared to saltwater salmon. Saltwater salmon tend to have a silvery coloration, while freshwater salmon may have a more mottled appearance. Additionally, freshwater salmon must migrate to the ocean to mature and spawn, while saltwater salmon complete their entire life cycle in the ocean.