The phrase "Marine" is commonly used as a salt water term; but technically refers to anything living in, on, around, or having anything to do with a body of water.
True salt water (marine) fish do not have the required evolutionay developments to cope with living in fresh water. Brackish water or Estuarine fish can be aclimatised to live in fresh water for a considerable time but eventually they will need a return to salt water otherwise they get sick.
"Biologist" is a very general term, referring to someone who studies any living organisms. A "marine biologist" is a type of biologist who studies organisms that inhabit a salt water environment (sometimes "marine" refers also to fresh water, but usually it is specific to salt water).
Because marine fish live in salt water because there found in the ocean.
It is a marine fish found in the atlantic ocean.
Some marine fish can live in fresh water. But most marine fish are adapted to salt water; because of the salt in the water their body needs to do things differently, and they are used to being in salt water. If you put them in fresh water, their body can't do the same thing, therefore most of them die. For more information, see the related question.
Fish are a part of the marine biome. There are two forms of marine biomes: fresh water biomes and salt water biomes.
Marine fishing refers to fishing in the ocean/salt water. Some species of fish migrate from salt to fresh water like the salmon.
Fresh water and marine or seawater are differentiated primarily by the amount of salt they contain (fresh water has almost no salt, sea water has about 3.5% salt by weight) and where you find them. To identify marine or sea water there is only one criteria, it is found in the oceans or salt seas. This differentiation is essential as the Black Sea is a freshwater sea. The fact that it is salty is shared with salt lakes and salty ground water. Likewise fresh water has little or no salt and is found in some but not all lakes and rivers and in underground water. Precipitation is generally fresh water as is meltwater from glaciers and the ice caps.Potability (can you drink it) is never a characteristic of sea water due to the salt, but fresh water is not always potable. It may contain metals, bacteria, odours, chemicals and similar materials.
The fresh water better than the salt water because the salt water has salt and that's not good for the living things
marine biome and the freshwater biome
Marine birds and reptiles have glands that secrete excess salt from their systems.