The sex changes of shellfish and cultured shellfish are mostly hermaphroditic, but hermaphroditic species are also quite common. In hermaphrodite species, most of them are hermaphroditic, that is, the secondary sexual characteristics of both sexes are not obvious, so it is difficult to distinguish between males and females according to external sexual characteristics. Only a few species are hermaphroditic, that is, the secondary sexual characteristics of both sexes are more distinct, so we can distinguish males from females according to their external sexual characteristics. Hermaphroditic species are very common in Claudiobranchia, Claudiobranchia and Gastropoda, such as Claudioside, Scallop, Clam Anodonta, Clam Globularis, Clam Pea, Clam Mondego, Clam Meretrix, Shipworm, Foraminifera, Clam Meretrix and so on. The genus of Prebranchiae is hermaphroditic, such as Eupolyphaga, Eupolyphaga, Lepidoptera, Conch, Oncomelania, Concha cylindrica, Oncomelania, Chiroptera, Cephalosporin, Oncomelania and Quercus. Shellfish can be divided into hermaphroditism and hermaphroditism, but this distinction is not constant. Androgynous species can have sex reversal and exchange sex, and hermaphroditic species can also become hermaphroditic because of gender change. The sex changes of gastropods such as sail snail, crucible snail and shoe snail are significant. An individual is a male when he is young and becomes a female when he is fully grown. This is because the testis and mating organs are gradually shrinking, and the ovary is gradually developing into a female stage. In the process of this personality change, there is a gradual change, and there is a period of doubt in the gradual change; There is a mutation, that is, male traits are quickly replaced by female traits. Octopus, for example, is male when it is young, but some individuals have follicles mixed in their seminal vesicles, which fully play the role of male at the first sexual maturity and soon become female when the environment is suitable. Oysters are hermaphroditic species, but they are not absolute. Some individuals' masculinity (or femininity) is very strong, while femininity (or masculinity) only shows traces. Individual individuals are only females (or males), that is, they become hermaphroditic. Concha plicata and Crassostrea gigas are hermaphroditic species, but a few individuals are hermaphroditic, and their sex can be changed. Why is there a phenomenon of degeneration? It is still a mystery. Many scholars have different views, which can be summarized as follows: water temperature: According to experiments, the sexual change of mussels is related to water temperature. When the monthly average water temperature is 13.2- 19.9℃, the proportion of male individuals is high; When the monthly average water temperature rises to 20-29.3℃, the sex ratio is close. When the water temperature drops, the male individuals increase again. It can be seen that male individuals with low water temperature are dominant. Substitute: Oysters come in two genders. When the metabolism of protein in the body is vigorous, the female period is dominant; When carbohydrate metabolism, especially glycogen metabolism, is vigorous in the body, the male phase is dominant. Nutritional conditions: A comparative experiment was carried out in a farm, and it was found that female oysters were dominant in the case of superior environmental conditions, while male oysters were dominant in the case of poor nutritional conditions. Male precooking: Some scholars believe that nutritional conditions are not the factors that determine the sex of oysters, but are caused by male precooking. Ostrich, for example, are all males when they are young, even in the case of excellent nutritional conditions. This is because the gonads of young oysters are bisexual, and the sex is often changeable. But in general, due to the rapid formation of sperm, they often appear male at the first sexual maturity and return to bisexual state after the breeding season. What kind of traits are displayed in the second year is determined by nutritional conditions. When the nutritional conditions are superior, oysters grow big and fat, which stimulates the formation and growth of oogonia and inhibits the formation of spermatogonia, resulting in an increase in the proportion of female oysters. Hermit crab: Some scholars have found that bean crabs often live in the fur cavity of oysters, and the number of males living in oysters with bean crabs has increased significantly, which shows that hermit crabs are related to sexual change. The multi-branchial, dense-branchial, bipedal and primitive gastropoda of shellfish have no mating apparatus, so they can't mate. They can only be fertilized by the germ cells discharged by their parents in seawater, or the males discharge their sperm into seawater, and then they are inhaled by the females and fertilized in the gill cavity or fallopian tube. Cephalopod males have one or a pair of specialized stylized wrists to mate with females. There are two ways, one is that the stem wrist can automatically fall off to mate with the female, and the other is that the stem wrist can't fall off as a medium organ for transmitting reproductive products. Squids have rear-end collision when mating. After a period of rear-end collision, the male first turned to the female, tilted the first pair of wrists upward, and the female spread her wrists radially, protruding the oral membrane. At this time, the male quickly confronted the female, crossed each other with two or three pairs of wrists and hugged each other's heads tightly. Finally, the male hooked a pair of sperm pods discharged from the funnel mouth with the sucker on the fourth wrist on the left, and quickly transported them to and adhered to the female oral membrane. The mating time varies, generally 2- 15 minutes. After the first mating, if the male still does not leave the female, it is possible to continue mating. Octopus also has the phenomenon of looking for a mate. Once the male que meets the female que, the third wrist on the right side, that is, the wrist crossing, slowly reaches behind the female que. When the tip of the wrist-delivering device touches the coat cavity of the female que, the tip of the wrist-delivering device immediately turns back to hook it and insert it into the coat cavity of the female que, and the milky white sperm pod sprayed from the funnel mouth is sent into the coat cavity of the female que by the suction cup. The whole process only takes 3-4 seconds. Octopus mate in pairs, but there are also two males mating with one female at the same time, and fertilization of sperm and eggs is mostly carried out in the coat cavity. Hermaphroditic gastropods also need to mate during reproduction. During mating, the male's mating process is that the penis extends into the female's mating sac, where the sperm meets the egg passing through the fallopian tube to complete fertilization. Most hermaphroditic gastropods cannot self-fertilize because sperm and eggs cannot mature at the same time, so cross-fertilization is also needed. For species that have bisexual pores but are far away, such as sea rabbits, many individuals are usually arranged side by side during mating. The first individual plays the role of female, the last individual plays the role of male, and a series of individuals in the middle play the role of male and female. In other words, the penis on one side of the second individual extends into the joint capsule of the first individual, while the joint capsule on the other side is inserted by the penis on one side of the third individual, and so on, and the penis on one side of the last individual extends into the joint capsule of the penultimate individual. In species with hermaphroditic holes but far away, there is also the phenomenon that only two individuals mate. In this way, only one individual plays a male role, while the other plays a female role. For species with only one homogeneous pore, such as pulmonary snails, mating can only be carried out by two individuals. At this time, both of them play the dual roles of men and women, that is, mutual fertilization. Hermaphroditic shellfish, some of which can fertilize themselves. Such as oyster, lung snail, basal snail, Brachionus rotifer, flat jade snail, Ayong slug, begonia, bigeye snail, etc. Self-fertilization is quite common. There are two ways of self-fertilization. One is that eggs and sperm from the same reproductive nest are directly combined with fertilization when they are moved to the reproductive tube. Second, the penis is inserted into the female tube for self-mating and fertilization, which only exists in vertebral snails and flat jade snails. Some shellfish can parthenogenesis, that is, eggs can develop independently without sperm. It is reported that gastropods have parthenogenesis. To sum up, shellfish culture methods are ever-changing. Some can parthenogenesis without fertilization, some have in vitro fertilization and development, some have mating devices for in vivo fertilization and development, and some have in vivo fertilization and development. It can be seen that everything in the world is full of wonders.