Eternal return: amazing facts from the life of salmon

His whole life is one long journey, back and forth. After thousands of kilometers, he carries with him the smell of his native stream. Parasites help him, and his brothers from farms kill him. We have collected amazing facts about such seemingly understandable salmon.

If you build a rating of animals for the love of a small homeland, salmon would take the first place in it. After living for some time in their native stream, the fish go on a grand journey to the sea. Those who get there alive, feed for several years and save up their strength to one day swim back to the place of birth and die there.

When salmon hatch from eggs, they have a huge (relative to their own size) yolk sac. It stores a supply of nutrients for the first days. The juveniles learn to swim, and then those who survive begin to rapidly change their appearance. Salmon are able to transform, as few people in the animal world. Young salmon that feed near the place of birth are called fry. Those who go out into the river and acquire a mottled camouflage color are called mottled. Rolling down (a special term that denotes young fish aspiring to salt water) in the sea — smoltami. Silvery smolts are so different from motley that they cannot be mistaken for representatives of the same species. What can we say about how the fish look during the spawning period, in a bright mating color! Due to the fact that salmon constantly change their appearance during their life, there is some confusion in the names of the fish. For example, salmon is a certain type of Atlantic salmon, and trout is a freshwater form of different fish. So the same fish can be called, for example, chum salmon, salmon and trout — and all this will be correct.

In the Far East, fish breeding plants annually release 800 million fish into the ocean

Most of the salmon are grown on special farms, where up to half a million animals are kept in nets. Farms compensate for the steady decline in the number of wild salmon, but a meeting of a traveler hurrying to the sea with a brother who grew up in artificial conditions can be fatal for the first. Not so long ago, scientists found out that it is on farms that the main parasite of fearless fish, the salmon louse, reproduces and goes wild. This sucker-like little crustacean feeds on blood. For adult salmon, lice are not very dangerous, but young fish that, rolling into the sea, pass by farms and pick up a parasite, are highly likely not to survive.

Sockeye salmon lays up to 10,000 eggs

During the journey, salmon becomes infected with many parasites, but some of them, as it turns out, prolong the fish’s youth, not letting them die prematurely. On the way to their native pond, many salmon acquire fellow travelers — larvae of bivalve pearl oysters. They attach themselves to the gills and travel with the fish. From two to seven thousand shellfish can “dig in” on one salmon. Until recently, biologists considered pearl oysters to be unconditional parasites that literally suck the juices out of fish, but in recent years this idea has begun to change due to new facts.

Field experiments with radio tags show that salmon infected with pearl oysters do not die more often than healthy counterparts. Moreover, it seems that shellfish slow down the aging of fish in cold climates. In the north, pearl oyster larvae need a lot of time to develop, so it is in their interests to prolong the life of the host salmon and not let it die too quickly. Some scientists believe that Atlantic salmon, unlike Pacific salmon, does not die after spawning precisely because of the joint evolution with pearl salmon. How exactly shellfish keep salmon young is still unclear, but theoretically it can be done, for example, by reducing the activity of adrenal hormones.

During the salmon spawning period, Kamchatka rivers literally boil with fish

Salmon find their way unmistakably in any weather and in any conditions. For a long time it was unclear how fish navigate in space even when neither the Sun nor the Moon is visible. Zoologists have long assumed that salmon, like birds, can navigate by the magnetic field, but it was not possible to confirm the hypothesis. I helped scientists… the Canadian island of Vancouver. It blocks the mouth of the river, where the salmon goes to spawn, so the fish have to go around the island along the southern or northern path, which are almost 400 kilometers apart from each other.

Armed with data on migration and changes in the magnetic field for 58 years, scientists have found that fish prefer the path that is more similar to the mouth of the magnetic properties of two years ago. That is, at the moment when the fish going to spawn left the river. This observation was the first direct proof that salmon with the help of special organs remembers the configuration of the magnetic field and is guided by it.

When salmon goes to spawn, a large male Kamchatka brown bear can eat several dozen fish per day

Salmon find their native backwater by catching individual molecules with their olfactory organs that carry a familiar aroma. In terms of sensitivity to odors, fish are only slightly inferior to dogs. In the 70s of the last century, American researchers discovered that the basis of salmon navigation at the last stage of the journey is olfactory memory. Zoologists raised a young coho in water with flavorings, and then released into the ocean. When the fish returned to their native places in due time, it turned out that they were easily led astray by simply adding an odorous substance to the water. Instead of the right pond, the coho and rushed to where its smell came from.

In order not to get caught by predators, fry (pictured) swim at night

The memory of flavors in salmon is formed not earlier and not later than a certain period. Biologists call this memory olfactory imprinting, because it seems to imprint the features of the environment at a certain point in life. A similar mechanism causes birds to consider as a mother the object (including inanimate) that they saw in a short, strictly limited period of time.

To catch salmon, fishermen put up “walls of death” from nets up to 12 km long, which do not allow the fish to return to their native places

During the spawning course, the salmon’s body undergoes dramatic metamorphoses: the color changes, the hump grows, the scales sink into the skin, a horny beak grows on the muzzle, and part of the internal organs disappears. On the way back to their small homeland, salmon do not eat, so their digestive organs atrophy, and until death, the fish live on accumulated fat reserves. Radically changing the appearance of pisces is caused by the same reason why girls wear high-heeled shoes, and young men spend long hours in the gym. In salmon, the requirements of sexual selection are much tougher: the brighter the individual, the easier it is for her to attract the attention of the opposite sex. Most fish die after spawning, so it makes no sense to save on resources, and salmon put everything on the line.

Stairs to the homeland

Hydroelectric power stations have been built on many rivers where salmon spawn, and the channels are blocked by dams. For a long time it was believed that hydroelectric power plants are extremely dangerous for fish.

Relatively recently, hydroelectric power plants, and especially their turbines, really were a deadly obstacle for salmon. But today, at most stations, special “water ladders” are arranged, along which fish can climb into their native reservoir, bypassing the blades. However, the movement to the sea was still considered dangerous for young fish: experts believed that salmon could not navigate in the water without a current, in addition, in shallow streams, fish become easy prey for predators.

Fortunately, recent experiments with radio tags have shown that smolts who swim on a river with dams have no less chance of reaching the sea than in rivers without dams. The results of the study are encouraging, but most salmon populations are still declining due to human activity.

Salmon travel hundreds of kilometers without interacting with anyone from a huge herd, but in the last days of their life they find the other half to do the main thing. Salmon spawn on shallow river rifts with a pebble bottom. Females dig a hole up to half a meter deep, where they spawn. After fertilization, the fish dig up the pebbles a little upstream so that the water flow fills the nest with it. A spawning mound with a height of 10-20 centimeters and an area of several meters is formed above the caviar. A muddy or clay bottom is not suitable for caviar — a constant current of clean, oxygen-rich water is needed.

Unfertilized eggs are carried away by the current

There are from one and a half to five thousand eggs in the clutch, depending on the type of salmon. The record, about 14,000 eggs, belongs to the chinook salmon, the largest of the salmon fish. Oddly enough, most of the caviar usually survives. But one of two hundred brothers and sisters manages to make a trip to the sea and return to their native places.

Future
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Atlantic salmon, apparently, will be the first genetically modified animal to hit the shelves of stores. GM fish already exist, but opponents of any interference with the genome do not allow scientists and fish farmers to start breeding.

Work on the creation of fast-growing salmon began in 1989 and was completed in six years. The American company AquaBounty has embedded a growth hormone gene with increased activity in salmon chromosomes. The modification makes it possible to grow salmon to marketable size twice as fast: not in three years, but in eighteen months.

The US FDA has confirmed the safety of its consumption, but GM salmon is still in the networks of bureaucracy. Approvals are endlessly delayed, and the company has every chance of going bankrupt.

In the habits of salmon, you can find enviable patriotism, self—denial for the sake of the future, and incredible determination – everything that people appreciate so much. However, a person’s desire to endow the surrounding world with meaningfulness says a lot only about a person. And the salmon…

“The fish doesn’t think,” sang Iggy Pop, —because the fish knows. Everything.”