https://fisheries-bio.blogspot.com/2023/01/what-is-fish-define-fish.html

Fish are aquatic animals that are typically cold-blooded, have fins and scales, and breathe through gills.
They come in a wide variety of shapes, sizes, and types, and can be found in both saltwater and freshwater environments all over the world.
Fish are a diverse group of animals, and they can be divided into many different classes, including bony fish and cartilaginous fish.
Bony fish, such as salmon and tilapia, have a bony skeleton and a swim bladder that helps them control their buoyancy.
Cartilaginous fish, such as sharks and rays, have a skeleton made of cartilage and no swim bladder.
Fish are an important source of food for both humans and other animals, and they also play important roles in many aquatic ecosystems.

Different between freshwater fish and saltwater fish (saline water fish)?

 Freshwater fish and saltwater fish are adapted to different environments and have some key differences.

 Freshwaterfish live in, you guessed it, freshwater, such as rivers, lakes, and streams.

They are adapted to a lower salt concentration in their environment and have specialized mechanisms to maintain a balance of fluids in their bodies.

As a result, they have a lower tolerance for changes in salinity and can't survive in saltwater environments. Some examples of freshwater fish include bass, trout, and catfish.

Saltwater fish, on the other hand, live in saltwater environments such as oceans, bays, and estuaries.

They are adapted to a higher salt concentration in their environment and have specialized mechanisms to deal with the increased osmotic pressure. Saltwater fish have a higher tolerance for changes in salinity and can survive in a wide range of salinities.

Some examples of saltwater fish include tuna, salmon, and halibut.

 Another difference is the taste and texture of the flesh, where freshwater fish usually lean and flaky with a milder taste; while Saltwater fish usually have a higher fat content, and a stronger fish taste.

    Another consideration is the fishing gear, freshwater fishing typically requires different equipment than saltwater fishing because of the different species and environments in which they are found.

 It's worth noting that some species of fish are able to adapt to either fresh or salt water, like salmon and eels which have been observed to have life cycles that include both environments. 

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