Goldfish ancestors invented an original aging mechanism

Currently, the generally accepted version of the origin of numerous breeds of goldfish is the domestication of its ancestral form in China around the 7th century AD. According to this theory, the initial material for selection was individuals of the Chinese subspecies of silver crucian carp (Carassius auratus auratus) living in southern China. However, the “authorship” of the creation of the Chinese goldfish by the Chinese may be questioned in connection with the findings of possible wild ancestors of the domesticated goldfish ... in the reservoirs of South - Eastern Europe.

If you think that goldfish are born gold, then you are mistaken. The fry of a goldfish up to the age of 1-2 months looks rather modest: it is an ordinary silver-gray fish. Then the back darkens, spots appear, the color changes more and more towards gold and red. In domesticated breeds of goldfish, this "molting" occurs quite early, even before puberty. This is beneficial to breeders: you can quickly select the best color options. The sex of domesticated goldfish is genetically determined: males emerge from some eggs, females from others. Also, there are no known cases of gender change - throughout life, males remain males, and females remain females.

At the beginning of the 21st century, the famous Russian ichthyologist Sergei Borisovich Podushka in the North Caucasus discovered a wild form of a goldfish, which he later called the commercial goldfish.А

For several years, Sergei Borisovich studied PZR in aquaculture. It turned out that this form is gynogenetic, in nature it is represented only by females. Gynogenesis is a form of reproduction in which the egg develops without fertilization, and the sperm serves only as an incentive to begin its development. The mere fact that PZR is a gynogenetic form suggests an idea of ​​its natural origin. Indeed, among the numerous breeds of the goldfish, the gynogenetic forms are not known. Crossings of domesticated goldfish with silver crucian carp when the first one got into natural reservoirs have repeatedly occurred, but there were no cases of parthenogenesis in such hybrids. Subsequently, it turned out that part of the PZR in the process of individual development can "turn" into males. The males showed normal "male" behavior, chasing females during spawning. However, it turned out to be practically sterile. The transformation of females into males in fish is not something extraordinary - in the experiment this is done by adding the appropriate sex hormones, for example, testosterone, to the water. But males at the same time are completely fertile, with normal spermatogenesis.

As a result, males of PZR lost fertility? It seems plausible that for many generations of clonal propagation, natural selection did not affect the genes associated with spermatogenesis, and as a result of the accumulated spontaneous mutations, these genes were simply “spoiled”. Thus, by the number of mutations accumulated during the period of clonal reproduction of PZR in certain genes, and knowing the rate of spontaneous mutagenesis in these genes, one can determine the age of origin of this form.

But what about color changes? PZR "fade" at the age of 3-4 years, and it is very uneven, some earlier, others later. And some may retain their original silver-gray color for several years, but at the same time they become sexually mature at the age of a year.

It can be assumed that the color change in PZR is an adaptation that allows more efficient use of the limited fodder resources of small, and often drying out steppe reservoirs in which PZR could inhabit. Larger fish that changed color to red were eaten away by predators, as a result of which relatively small, but already mature and numerous silver-gray fish gained an advantage in procreation.

We observe a similar adaptation in many plants: when the seeds ripen, the fruits gradually acquire a bright color, as if inviting various animals: “Eat me!”
Such adaptation in PZR is not beneficial to a single individual, but allows the population as a whole to exist more successfully. It could arise in the form of a mutation in one or more individuals in a small closed population. If clonal reproduction arose earlier than the ability to change color, the absence of intrapopulation crossing could support the spread of this mutation.

Unfortunately, there are no answers to all the questions posed yet. And this is largely facilitated by the secrecy that has arisen around the topic of PZR. Numerous publications by SB Pillows gradually disappear from the Internet. The aquaculture of PZR has been transferred to the All-Russian Scientific Research Institute of Fisheries and Oceanography (VNIIRO), and for several years now it has been “about neither hearing nor spirit”. No one knows what VNIIRO experts found in the PZR, why there are no publications, at least in Russian.

The phenomenon of commercial goldfish may prove worthy of publication in prestigious scientific journals such as Nature, and shed light on many issues related to the emergence of gynogenesis, evolution and aging of organisms.

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