Salmon, also known as "salmon", is an anadromous fish belonging to the family Salmonidae. When autumn comes, mature salmon swim back from the Sea of Okhotsk into Heilongjiang in droves and come to their original breeding grounds to lay eggs. Salmon has a tenacious will, and it can rush through no matter how fierce the water is on its way home. Their speed of tracing back along the river is quite amazing, and they can swim 30-50 kilometers upstream every day and night, which is worthy of being the champion of fish "long-distance swimming competition". On the way back to the river, the body color of salmon also changed. At first, the color was very bright, and the back and side were yellow-green, and gradually darkened with time, showing cyan-black and silvery white abdomen. There are orange-red marriage spots on the side of the body, about 1 1, and the color of female fish is stronger than that of male fish. When you reach the spawning ground, the color of your body is darker. Salmon should choose the river section with clear water, gravel bottom and spring water as the spawning ground. Salmon spawning is also very interesting. They don't just lay eggs casually, but they have to make some preparations. When they arrive at the spawning ground, the female fish swims sideways, and constantly beats the gravel with the tail fin. By the impact of the current, a pit with a diameter of about 100 cm and a depth of about 20 cm is formed, and then the crystal orange eggs with a diameter of 5.6-6.5 mm are laid in the nest. When the female fish ovulates, the male fish is inseparable from the female fish like a guard, and constantly rubs against the female fish. When other male fish are found trying to get close to their "partner", they will be expelled immediately. When the female fish ovulates, the male fish also arranges the sperm in the spawning bed, and the eggs and sperm are fertilized in the bed. After ovulation and ovulation, the female fish repeatedly poked the gravel with the tail fin to bury the fertilized egg. The female and male fish still don't leave, but wander around the spawning ground. Salmon died soon after completing the task of reproduction because of the long and arduous return tour, spawning and exhaustion of physical strength. After a winter of low-temperature cultivation, the fertilized eggs hatch into larvae in the next spring. After about 30 days, the yolk sac disappears, and the larvae embark on a long journey and enter the sea with the river to grow.