Significant shift in the direction of the relations of organisms of one sex has both theoretical and practical importance, since one of the floors are usually more productive. It has long been observed that female fish exposed certain conditions (environment, hormones, etc.) are transformed into males (gambuzievye, melanohromisy, etc.). Female sex hormone (estrol) and male (methyltestosterone), when added to water or feed override the floor. Japanese geneticist Yamamoto in 1969 turned the females in the male goldfish. With further dilution of all offspring was female.

To date, aquaculturists have learned to change the sex of fish, affecting small doses of hormones on spawn. Also, damage to the endocrine system of fish themselves may cause preferential birth of individuals of one sex. Scientists have reported that emissions of industrial plants cause disturbances in the endocrine system of fish in the early stages of development, which dramatically alters the sex ratio towards males for priority development. But the most interesting – it is social factors of change of sex – that is, adult mature fish change sex at influence “public opinion” so as to optimize the sex ratio in the population. What gives the fish change sex? Found that the number and quality of eggs is directly dependent on the size of females. For males there is no such dependence.

Therefore, a strategy in which the fish first enter into a breeding male, and having grown older and bigger, turning into females, it looks logical. The transformation of males into females under the influence of social factors has been well studied as an example clown fish. A young clown settles from the plankton to the reef under the protection of sea anemones. The biggest fish in the group is female, the second biggest – by a male. The remaining fish are still immature. But if the female dies, the clown-male quickly turns into a female, and the next largest fish matures as a male and takes his place. However, there are times when the success of reproduction depends on the size of males. In cases where the male to defend a harem, spawning territory or to protect the clutch of eggs, large males have an advantage over smaller ones. Therefore, in some species females grow up, grow up and turn into males. In the fish phenomenon often seen in cichlids. On Coral reefs are the fish that do not need to change sex, because they are both males and females. Such fish hermaphrodites mature and spawn, and milk. If two such individuals to meet and enjoy each other, each of them will breed. If there is not a worthy partner, then we can resort to self-fertilization. This strategy has the advantage of deep-sea fishes numerically small, are difficult to find a mate in the ocean depths. But so far committed is not clear why this should coral fish. Coral fish are hermaphrodites live fairly dense populations in which the choice of couples – not a problem. Moreover, the known types of hermaphrodites, which form permanent monogamous pairs for life.

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