Anadromous migration of salmon

Salmon is my country’s famous salmon. It usually lives in the waters north of 350N in the Pacific Ocean. They live in the ocean for 3-5 years. Every autumn, they cross the Sea of Okhotsk in groups, bypass Sakhalin Island, and enter the Heilongjiang, Suifen River and Tumen River systems. You can reach the Ussuri River Estuary in early September. Salmon swim upstream very fast, reaching 30-50 kilometers per day and night. It arrives at the spawning ground from late October to mid-November, and the journey is about 1,500 kilometers. The broodstock will die after spawning. The following spring, the larvae flow into the sea along the river.

In the vast oceans and wide rivers, the question of how salmon find and return to their birthplace has attracted the attention and research of many ichthyologists. In the early 1950s, Mr. Hassler used cotton to plug the nostrils of salmon for field experiments. He found that these individuals with an impaired sense of smell lost the ability to return to their original place of birth, while individuals without cotton plugged did not. Affected. In the early 1970s, he used a chemical agent, morpholine, to sprinkle into the water to create an artificial "home smell". He conducted regression experiments on coho salmon domesticated in the Great Lakes of the United States and achieved success.

In the experiment, a small ultrasonic transmitter was inserted into the fish's stomach, and then an ultrasonic receiver was used to track the fish's activities. It was found that individuals treated with morpholine would not swim away when swimming through the water area dripping with morpholine. In addition, experiments were carried out by inserting small electrodes into the olfactory bulbs of the fish's brains, and then immersing the nostrils in various solutions. As a result, coho salmon treated with morpholine reacted most strongly to distilled water solutions containing morpholine, while untreated coho salmon showed no reaction at all. All experiments show that salmon migration uses the sense of smell to identify "home smell". As for what conditions they rely on to swim to the mouth of the river where they were born on the vast sea, there is currently no direct evidence. It is generally believed that migratory fish may have a sun compass mechanism. Because there are examples of fish that rely on the sun for orientation. For example, the white wolf perch can swim directionally from the center of the wide lake to the spawning ground on the lakeshore on a sunny day, but on a cloudy day it cannot identify the direction and cannot return to the spawning ground. This shows that the sun It serves as a directional guide for some fish species. This mechanism has been reported in some birds and insects.

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