Is a shark a fish? a shark is a fish. It belongs to Chondrichthyes, including 8 orders and 25 families, namely Hexanchiformes, Lamnidales, Heterodontiformes, Carcharhiniformes, Squalidae, Squalidae, Carcharhiniformes and Barbocephali. Usually marine organisms, a few can enter fresh water survival, swimming speed is relatively fast, large size. Its bones are composed of cartilage, which is often calcified.
1. Oviparous: Generally, large sharks are oviparous. They lay eggs with egg sheaths. These eggs can be attached to rocks or seaweed, which can effectively avoid predators. The egg sheath is generally a broad rectangle, the skin will harden when exposed to water, each corner has hollow horns, which can allow seawater to enter, thus providing oxygen to the eggs inside. Usually the eggs hatch after a few days or weeks, and the mother leaves them alone.
2, viviparous: pelagic sharks usually use the method of viviparous, fertilized eggs outside the horny shell, generally in the uterus development. In the process of its growth, the mother will secrete uterine fluid and other nutrients to provide nutrients, until the larvae are fully formed, they will be discharged, usually producing ten tails at a time. The advantage of viviparity is to ensure the growth and development of larvae, but also to provide a place of shelter, after birth can survive in the sea.
3, ovoviviparity: ovoviviparity is similar to viviparity, will also be in the body of the embryo, until the young grow out. But the difference with the viviparous is that the shark mother will not provide direct nutrition, fertilized eggs generally through the absorption of unfertilized eggs to obtain nutrients, each time can also produce ten, but the huge whale shark each time can produce about 300.
