Most known fish breed by spawning, but not all. Some underwater inhabitants, both aquarium and wild, give birth to their offspring. Therefore, many lovers of aquatic fauna are interested in the question of which fish are viviparous and how exactly they reproduce.
Sharks
Many sharks are known for being viviparous. For example, such species include tiger, herring, frilled sharks, hammerhead fish and others. Also on this list is the blue shark. The size of this fish usually does not exceed 3.8 meters. But their sexual maturity begins when they reach two meters. In males, this period begins at a body length of 1.9 meters.
After copulation has taken place, the female may not become pregnant immediately. The spermatozoa in her body are able to persist for months, waiting for the period of ovulation. After the eggs of the female have been fertilized, she begins a gestation period, which can last from 9 months to a year. It is believed that the blue shark is one of the most prolific of all large relatives. The number of fry born is different, and the figure varies from 4 to 120 individuals. Babies are bornindependent, ready for predatory life, but only half of them reach their sexual maturity, because larger fish are not averse to profiting from them.
Scatfish
But this way of breeding fish is not only found in sharks. Some species of rays are also viviparous, such as stingrays. Usually the female brings one baby, whose length is about 35 centimeters. Viviparous stingrays also include manta rays, which have another name - sea devils. These large fish also bring one baby, which at birth already reaches a meter, and its weight is 50 kilograms. In order for the offspring to be born, the mother seems to shoot her baby, which is rolled up. The baby immediately spreads its "wings" and swims after the female. During pregnancy, this fish shows unprecedented aggression and is able to flood the boat.
How do babies develop in the womb?
It is known that a viviparous fish brings an already formed baby, but for many years scientists could not understand how fry receive oxygen in the womb if they do not have a placenta and an umbilical cord. But in 2008, the mystery was solved. Okinawan fishermen caught a pregnant sea devil and left it for scientists to study. In order to better understand the gestation period of this fish, the researchers slightly improved the ultrasonic device, after which it began to work in s alt water. Observations continued until birth, which occurred eight months later. One baby was bornfemale. The newborn weighed 50 kilograms.
Because this viviparous fish was observed throughout the gestation period, scientists were able to unravel the mystery of how the fetus breathes. While in the womb, the baby uses its gills and pumps amniotic fluid through them. To do this, he, like an adult, opens and closes his mouth. The water that gets to it passes through a special channel and reaches the valve behind the head (not only stingrays, but also sharks have it). Adults do not close their mouths when moving in order to immediately filter water and plankton. Babies in the womb have to use their mouth as a pump. In this way, the fetus can both breathe and eat.
Relationship between parents and fry
Because the cubs are ready to lead an independent life immediately after the appearance, they basically do so. Most of them are no longer dependent on their mother. And in some cases, it is better for them to stay away from their parents. Adults usually do not distinguish their offspring from food, and if they are hungry, they can profit from their own babies.
Other species of viviparous fish
The sharks and rays described by us are cartilaginous fish. Among bony fish, those that reproduce by spawning are more common. But still among them you can meet and viviparous. These include Cymatogaster. This type of fish is similar in some factors to perch, and in other ways it resembles cyprinids. Their habitat isPacific Ocean, northern part.
But viviparous are not only fish in which fry feed directly from the mother in the womb. The female can carry eggs in her belly. The fry feed on the yolk. When the time comes to give birth, the eggs are formed into fry and the mother begins to throw them. For example, this method of fish breeding is inherent in the eelpout. At birth, these fry are already formed. At a time, the female can bring up to three hundred fish, but this happens in portions. The size of each newborn fry is four centimeters.
Among commercial viviparous fish is sea bass. This is a very prolific species that is caught in large numbers in the Barents Sea and the Atlantic Ocean. This viviparous fish in one season gives birth to several hundred thousand. She tosses with larvae, each of which is approximately six millimeters.
The only viviparous fish of Baikal
Baikal is a beautiful and deep lake, and it is home to many underwater inhabitants. Among all the diversity here you can find the only viviparous fish, which is called golomyanka. This fact may seem surprising to many, since usually in the northern latitudes, fish reproduce by laying eggs. There are two types of golomyankas here. The large one grows up to 25 cm, the small one does not exceed 15 cm. The golomyanka does not make spawning migrations, as happens with other fish that spawn. When the time comes and in the womb of the female, the eggs turn into fry, the mother risescloser to the surface of the water. Most likely, this is necessary in order for children to feed on planktonic organisms. The viviparous golomyanka fish gives a large offspring, depending on the species. In small ones, no more than 1.5 thousand fish appear at a time. For large ones, this figure is approximately 2.5 thousand fry. After giving birth, the mother dies. Surprisingly, this species of fish is found only on Lake Baikal. A similar mechanism of reproduction and death is no longer repeated in other underwater inhabitants.
Aquarium inhabitants
But viviparous fish are found not only among commercial fish species. Many aquarium owners know that some of their pets carry their fry. Basically, live birth is inherent in the family of Pecilia, Goodiaceae and some others. They are usually schooling fish and are small in size. Also among them, males are slightly smaller than females, and their colors seem brighter. When they reach puberty, the anal fin of the male becomes a gonopodia, with the help of which fertilization occurs. Each species has its own distinctive features in the structure of this process. This is necessary in order to exclude the possibility of hybridization. But breeders annually bring out new varieties of ornamental fish, which leads to the appearance of unusual colors and shapes. This is especially true for guppies. Without selection, decorative viviparous fish quickly lose their color and gradually degenerate.
Fry Development
Development period from caviar tofry in the womb of the female depends on the family and species of fish. After fertilization, gestation can last only a week or two. But in some fish this period lasts up to 2.5 months. In most livebearers of the Pecilia family, the young are large and much lighter than the eggs themselves, while in other species the weight of the fry is much greater than the fertilized eggs. And due to the fact that the milk from the male can remain in the female for a long period, the eggs can not be fertilized immediately, but after a while and more than once. Therefore, even with a single fertilization, the fish is able to bring offspring several times. It is not difficult to feed him, since the fry immediately show activity after birth. The number of juveniles depends on the type of fish and can range from a few to hundreds.
Keeping livebearers
In order for the reproduction of viviparous fish to be successful, it is important to take care of their living conditions. For their maintenance, common aquariums are usually suitable, in which there are vegetation thickets. In addition, neutral water requires regular replacement. 15 to 40% fluid is changed weekly. But some species will feel much more comfortable if the water is lightly s alted. Such conditions are created mainly for mollies and whitenesoxes. To do this, a tablespoon of sea s alt is added to ten liters. Also the ideal water temperature for most species usually ranges from 20 to 25 0C.
In order for the diet of fish to be balanced, they need to add plant components to the feed. It can be lettuce, filamentousseaweed, oatmeal and other foods.
