Pregnancy has traditionally been defined as the period in which the developing embryo is incubated in the body after sperm-egg intercourse. Although this term often refers to placental mammals, this term has also been used in the title of many international scientific articles, reviewed by peers, for example, about fish, eg Consistent with this definition, there are several modes of reproduction in fish, giving the number of parental care different. In ovoviviparity, there is internal fertilization and the young are born alive but there is no significant placental or trophic interaction (eating); mother's body maintains gas exchange but the unborn baby is fed with egg yolks. There are two types of viviparity in fish. In histotropic viviparity, the zygote develops in the female ovum, but it does not provide direct nutrition; the embryo survives by eating its egg or its unborn sibling. In hemotropic viviparity, the zygote is preserved within the female and is nourished by it, often through some form of placenta.
On seahorses and pipefishes, men become pregnant.
Video Pregnancy in fish
Type of reproduction and pregnancy
Pregnancy is traditionally defined as the period in which embryonic development is incubated in the body after sperm-egg intercourse. Despite the strong similarity between viviparity in mammals, researchers have historically been reluctant to use the term "pregnancy" for non-mammals because of the highly developed form of viviparity in eutherians. Recent research into physiological, morphological and genetic changes associated with fish reproduction provides evidence that incubation in some species is a highly specialized form of reproduction similar to that of other viviparities. Although the term "pregnancy" often refers to eutherian animals, it has also been used in the titles of many internationally reviewed, scholarly scientific articles on fish, eg.
Five modes of reproduction can be distinguished in fish based on the relationship between the zygote (s) and the parent:
- Ovuliparity : Egg fertilization is external; the zygote develops externally.
- Oviparity : Egg fertilization is internal; the zygote develops externally as an egg with a large vitellus.
- Ovoviviparity : Fertilization is internal; the zygote is maintained in women (or men) but without major trophic interactions (eating) between the zygote and the elderly (there may be minor interactions, such as water conservation and oxygen levels). The embryo depends on its yolk to survive.
There are two types of viviparity among the fish.
- Histotrophic ("tissue eating") viviparity : The zygote develops in the female ovum, but it does not provide direct nutrition. The embryo survives by eating eggs or unborn siblings.
- Hemotrophic ("eating blood") viviparity : the zygote is preserved within the female and is nourished by it, often through some form of placenta.
Ovoviviparous Fish
Examples of ovoviviparous fish are many squaliform sharks, which include sand sharks, mackerel sharks, nurse sharks, shark requiem, dog sharks and hammerheads, among others, and coelacanth finned lobes. Some species of rockfish ( Sebastes ) and sculpins (Comephoridae) produce rather weak larvae without egg membranes and also, by definition, ovoviviparous. Ovoviviparity occurs in most live bony fish (Poeciliidae).
vivipar fish
Vivipar fish include the family of Goodeidae, Anablepidae, Jenynsiidae, Poeciliidae, Embiotocidae and some sharks (some species of shark requiem, Carcharinidae and hammer, Sphyrnidae, among others). The halfbeaks, Hemiramphidae, are found in both sea and freshwater and they are species that produce sea eggs with extended filaments attached to floating or stationary debris, while those found in fresh water are vivipar with internal fertilization. The Bythitidae is also viviparous although one species, Dinematichthys ilucoeteoides , is reported to be ovoviviparous.
Aquarists generally refer to ovoviviparous and viviparous fish as "livebearers". Examples include guppies, mollies, moonfish, platys, four-eyed fish and sword tail. All these varieties show signs of their pregnancy before birth live. For example, female and guppy swordtail will give birth anywhere from 20 to 100 young lives after a four to six week gestation period, and mollies will produce children aged 20 to 60 years younger after six to 10 weeks' gestation..
Maps Pregnancy in fish
Nutrition during pregnancy
Another term related to pregnancy in fish relates to differences in the mode and level of support given by females in developing breeds.
"Lecithotrophy" occurs when the mother provides the oocyte with all the resources needed before conception, so the egg does not depend on the mother. Many members of the Poeciliidae family of fish are considered lecithotrophic, however, research increasingly suggests that the others are matrotrophic.
"Viviparity Aplacental" occurs when women retain the embryo during the entire developmental time but without nutrient transfer to the young. The yolk sac is the only source of nutrients for developing embryos. There are at least two exceptions to this; some sharks get food by eating unfertilized eggs produced by the mother (oophagy or eating eggs) or by eating unborn siblings (intra-uterine cannibalism).
"Matrotrophy" occurs when the embryo secretes an egg yolk supply early in the pregnancy and the mother provides additional nutrients. Post-nutrient transfer of nutrients has been reported in several species within the genus Gambling and Poecilia, , G. holbrooki , G. gaigei , G. geiseri , G. nobilis , < i> P. formosa , P. latipinna , and P. mexicana .
Vivipar fish have developed several ways to provide their offspring with nutrients. Nutri "embryotrophic" or "histrotrophic" occurs by the production of nutritional fluids, milk of the uterus, by the lining of the uterus, which is absorbed directly by the developing embryo. "Hemotrophic" nutrition occurs through the administration of nutrients between the maternal blood vessels and the adjacent embryo, the organ like a placenta similar to that found in mammals.
Comparison between species
There is considerable variation between species during pregnancy. At least one group of fish has been named according to the characteristics of the pregnancy. Surfperch, genus Embiotoca, is a saltwater fish with a period of three to six months of pregnancy. This long pregnancy period gave the family its scientific name from the Greek "embios" meaning "persistent" and "tokos" meaning "birth".
The table below shows the period of pregnancy and the number of children born for some of the selected fish.
- a Unlike other sharks, the yolk placenta is a round or round sac.
- b Initially, the embryo is sustained by the yolk sac, but then the placenta develops.
- c A bonnethead woman produced a pup with parthenogenesis in 2001.
- d Spadenose sharks have the most advanced form of placental viviparity known in fish, as measured by the complexity of placental connections and the difference in weight between eggs and newborns.
- e Eelpout sucks on its young embryo while still inside their mother's body, making it the only fish species to suck his offspring.
- f Only one pregnant woman is known to have been arrested; she brought six unborn babies.
- g 1 per uterine horn
Poeciliopsis
Members of the genus Poeciliopsis (among others) show the adaptation of a variable reproductive life history. P. monacha can be considered lecithotrophic because females do not actually provide resources for their children after fertilization. P. lucida shows intermediate levels of matrotrophy, which means that to some extent, the child's metabolism can actually affect maternal metabolism, allowing for increased nutrient exchange. P. prolifica is considered highly matrotrophic, and almost all the nutrients and ingredients necessary for fetal development are supplied to the oocyte after it is fertilized. This level of matrotrophy allows Poeciliopsis to bring several mains at different stages of development, a phenomenon known as superfetation.
P. elongata <,> P. turneri and P. presidionis form another clade that can be considered an outgroup to P. monacha , P.lucida , and P. prolifica clade. These three species are very highly matrotrophic - so much so that in 1947, C. L. Turner described follicular cells P. turneri as "pseudo-placenta, pseudo-chorion, and pseudo-allantois".
Guppy
Guppies are very productive livebearers that give birth between five and 30 fry, although in extreme circumstances, it can give birth to just one or two or more than 100. The guppy pregnancy period is usually 21-30 days, but may vary. The area in which the guppy's pregnant belly meets the tail is sometimes called "gravid patch", or "gravid spot". When pregnant, there is a slight change of color that gradually darkens as guppy progresses through pregnancy. The first patch has a yellowish tinge, then brown and becomes dark orange as the pregnancy progresses. This patch is where the fertilized egg is stored and grown. Dark is actually a developing baby guppy eye and orange tinge is an egg like their jelly.
Elasmobranchs
The majority of elasmobranch are vivipar and show various strategies to provide nutritional and respiratory needs for their children. Some sharks only retain their children in the enlarged posterior segment of the fallopian tubes. In its simplest form, the uterus does not provide additional nutrients to the embryo. However, another elasmobranch develops a secretory uterine villi that produces histotrof, a nutrient that supplements the egg yolk store from oocytes. Uterine secretion may be the most advanced on the stingray. After the thinning of the egg yolk, uterine hypertrophy becomes the secretory complement of the so-called "trophonemata". The process by which uterine secretion (also known as uterine milk or histotrof) is produced to resemble breastmilk in mammals. Furthermore, milk is rich in protein and lipids. As the embryo grows, the troponemata vascularization enlarges to form a sinusoid that comes out to the surface to form a functional respiratory membrane. In lamnoid sharks, following the use of egg yolks, embryos develop teeth and eat eggs and siblings in the womb. There is usually one fetus per uterus and grows in large proportions up to 1.3 m long. In placental sharks, the yolk sac is not drawn to be inserted into the abdominal wall. Instead, it extends to form the umbilical cord and yolk sacs to be modified into functional epithelial placenta.
Male pregnancy
Male fish from sea horses, pipefishes, lean and leafy sea dragons (Syngnathidae) are unusual because males, rather than females, lay eggs before releasing live seeds into the surrounding water. To achieve this, the male sea horses protect the eggs in a special parent bag, the male sea dragon tying their eggs to their feet, and the male pipefish can also do so.
When a female egg reaches maturity, it sprays them from a room in its suitcase via an ovipositor into its parent bag or an egg bag, sometimes called a "marsupium". During mammalian pregnancy, the placenta allows the female to fertilize the seedlings inside the womb, and dispose of their waste products. If male pipefish and seahorse provide only simple bags for fish eggs to develop and hatch, may not fully qualify as bona-fide pregnancies. However, current research shows that in species of syngnathid with well-developed parent bags, males provide nutrients, osmoregulation and oxygenation to the embryos they carry.
Sea horses
When mated, the female sea horse stores up to 1,500 eggs (an average of 100 to 1,000) in a male bag, located in the ventral abdomen at the base of the tail. Male teenagers develop pockets when they are aged 5-7 months. Males carry eggs for 9 to 45 days until the sea horse appears fully developed, but is very small. The number born may be at least five for smaller species, or 2,500 for larger species. A male stallions have many prolactin, the same hormone that regulates milk production in pregnant mammals and although the male sea horse does not supply milk, its pockets provide oxygen and a controlled environment.
When the seed is ready to be born, the man expels them with muscle contraction, sometimes while gluing himself to the seaweed with his tail. Birth usually occurs at night, and a woman returning for a morning greeting routine finds her partner ready for the next batch of eggs.
Pipefish
Pipefish crushes their offspring either in different areas of their bodies or in parent pockets. Parent pockets vary significantly among different species of pipefish, but all contain small holes in which female eggs can be stored. The location of the parent pouch can be along the bottom of the pipefish or just at the base of the tail, like a sea horse. Pipefish in the genus Syngnathus has a ventral pouch with a ventral layer that can completely cover all of their eggs when sealed. In men without these sacs, the eggs stick to the soft skin curves on the ventral surfaces of their bodies that do not contain exterior coverings - a kind of "brooding skin".
At least two species of pipefish, Syngnathus fuscus and Syngnathus floridae , provide nutrients for their offspring.
The table below shows the period of pregnancy and the number of children born to some selected seahorses.
See also
- Reproduction of fish
References
Source of the article : Wikipedia
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