About the fish thing

Fish are the oldest vertebrates. Dwelling on the Earth they are almost all on the aquatic environment ? ? from freshwater lakes and rivers to the sea and the ocean salt water.

 World on the existing fish about 20,004 thousands. Living at sea from two-thirds, while the rest live in freshwater. China has 2 of 5 thousand 100 kinds, including for medicinal has more than 100 kinds of common medicinal animals have hippocampus, Dragon, eels, carp, crucian carp, sturgeon (fish glue for the Fish), large yellow croaker (otolith for the fish brain rock), sharks and so on. In addition, commonly used for the pharmaceutical industry of raw materials, such as cod, shark or ray of the liver are liver oil extract (vitamin A and vitamin D) of the main raw material. From a variety of fish in extractable hydrolyzed protein, cytochrome C, lecithin, cephalin, etc.. Puffer liver and ovary contains many tetrodotoxin can be extracted from the treatment of neuropathy, convulsions, such as tumor diseases. Large fish bile can distill "pigment calcium salt", for the artificial manufacture of raw materials Niuhuang. Fish of all the key link between the big difference as the key link between the terrestrial vertebrates. Is generally believed that fish are slippery and shaped body such as spindle, was streamlined, with fins, and gills of aquatic animals to breathe, but more the type that do not meet this definition. Some fish very long, some very short; some side flat, and some flat; Some fin large or complex shape, and some degradation as well digested; the mouth, eyes, nostrils, gill openings Change the shape of a great location; some fish breathing air, submerged in water it will drown. Fish are an important human food. Overfishing, pollution and climate change would destroy the fish resources. Predator fish larvae, can help control malaria and other mosquito-borne diseases. Fish is the behavior, physiology, ecology and medical importance of laboratory animals. Lot of fish feeding in order to watch, many species are fishing tours. Body length from less than 10 mm (0.4 inches) to more than 20 meters (60 feet) and weighing about 1.5 grams to about 4000 kilograms (8000 pounds). Many color and the environment consistent with the role of concealment. Some body-color bright, numerate, zebra, meaning there is identification. Some fish can reduce Zhang pigment cells change color, and some fish can be luminous.