Fish are vertebrates which are animals with backbone and they survive in water with the help of gills that help them to breathe. Their body is streamlined to suit swimming in water. There are as many as 25000 different types of fish in the different water sources all around the world. These fascinating creatures are found in almost every water source and environment. E.g.: Even in Antarctic a fish type called icefish is found and this fish survives in the water that is below freezing point. These different types of fish can include jawless fish, body fish and cartilaginous fish. Bony and cartilaginous fish have jaws. The size of fish can range between 8 mm to 45 foot.
Broadly fish may be classified into certain groups. These include tropical fish, coldwater fish, marine fish and freshwater fish.
These are the fish that live in either freshwater or saltwater but they need warm or tropical medium or temperature to thrive. Many types of tropical fish are popular aquarium fish because of their bright colors. The types of pet fish in tropical fish include wild caught specimens, single species that are individually born within captivity because of their peculiar features such as coloration or long fins and hybrids of multiple species.
These fish can be fresh water fish or salt fish and basically need colder water temperature. Typically these types of fish need temperature below 20 °C. Goldfish and koi are the most common types of fish in this variety. These fish tend to grow at a slower pace and also live longer than those that live in warm waters.
These fish thrive in salty seawater and most marine fishes require tropical climate to survive.
These are the fish that survive in freshwater and are usually found in inland rivers as well as streams.