At present, whale shark is the largest individual of all fish in the world. Whale sharks can reach 20 meters in length and 20 tons in weight, making them the largest fish in the world.
Marine fish are distributed from the poles to the equatorial waters, from the coast to the ocean, from the sea surface to the abyss of about 10 thousand meters. The diversity of living environment contributes to the diversity of marine fish. There are more than 20,000 kinds of live fish, among which marine fish is about1.20 thousand, which is the most prosperous fish group.
Marine fish have the same characteristics: gills that breathe dissolved oxygen in water, flippers that are easy to move in water, and skin that can secrete mucus to reduce the resistance to moving in water. In addition, it has its own characteristics in body structure, reproductive growth, feeding nutrition, exercise and so on. Marine fish is also an important industrial raw material.
Fish can be canned, fish liver can be extracted with cod liver oil, fish scales and bones can be made into glue, fish oil can be made into soap and lubricating oil, some shark skins can be made into leather, miscellaneous fish can be made into fish meal, and fish viscera and toxins of some toxic fish can be extracted into various medicines.