Fish are poikilotherms. Its circulatory system is very simple, because there is no fat layer under the skin, so it can not maintain its own body temperature, will change with the external environment. However, there are also a few fish with the ability to maintain body temperature, such as tuna, swordfish and so on, but compared with the real thermostat or a lot of poor, so also counted as poikilothermic animals.
1, herring: herring refers to the herring family of fish, its many types, the most common is sardines. The fish has a slender, silvery body with a short dorsal fin. They usually swim in dense groups, mostly feeding on plankton, and in the spring they lay eggs, which hatch in a few days, but drift with the water until they become real fish.
2. Swordfish: The swordfish is a marine fish of the genus Swordfish of the family Doradidae. Its body is streamlined, its body surface is relatively smooth, and its strong caudal peduncle can produce a huge driving force. Its upper jaw is like a spear, which can pierce the bottom of a boat when swimming at high speed. Because of its unique muscle and fat tissue, it can maintain a high body temperature in the sea and help swim to the depth.
3. Opah: Opah is a large marine fish of the family Lampridae. It is widely distributed in the warm water ocean. It has a high body and a small mouth. There are no teeth in its mouth. Because the whole looks like a flat and round big plate, also like the full moon, so get this name. It has strong adaptability to the environment, can live in warm water of 18-28 C, prefers weak alkaline water quality, and is not picky about food.
