Most fish known to us reproduce 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 to be viviparous. For example, such species include tiger, herring, shark- like sharks, hammer fish, and others. There is also a blue shark on this list. The size of this fish usually does not exceed 3.8 meters. But puberty begins when they reach two meters. In males, this period begins with a body length of 1.9 meters.
After copulation, the female may not become pregnant immediately. The sperm in her body can persist for months, waiting for the period of ovulation. After the eggs of the female have been fertilized, she begins the 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 that were born, varies, and the number varies from 4 to 120 individuals. Babies are born independent, ready for predatory life, but only half of them reach their maturity, because larger fish are not averse to eating them.
Cramp-fish
But this method of breeding fish is found not only in sharks. Some species of stingrays are also viviparous, such as stingrays . Usually the female brings one baby, whose length is approximately 35 centimeters. Viviparous slopes also include manti, which bear 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 as if shoots with her baby, who is rolled up. The baby immediately spreads its “wings” and floats behind 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 viviparous fish brings an already formed baby, but scientists for many years could not understand how fry receive oxygen in the womb if they do not have a placenta and umbilical cord. But in 2008, the riddle was solved. Okinawan fishermen caught a pregnant sea devil and left it to scientists for research. In order to better study the gestation period of this fish, the researchers slightly improved the ultrasonic device, after which it began to work in salt water. Observations continued until the birth, which occurred eight months later. One female cub was born. The newborn weighed 50 kilograms.
Since this viviparous fish was monitored for the entire gestation period, scientists were able to solve the mystery of how the fetus breathes. Being in the womb, the baby uses its gills and pumps amniotic fluid through them . To do this, he, as an adult, opens and closes his mouth. The water that enters it passes through a special channel and reaches the valve behind the head (it is found not only in stingrays, but also in sharks). Adults do not close their mouths when moving to immediately filter water and plankton. Babies in the womb have to use their mouths as a pump. In this way, the fetus can both breathe and eat.
Parent-fry relationships
Since the cubs are immediately ready to lead an independent life immediately after their appearance, they basically do this. Most of them are now independent of the mother. And in some cases, they’d better stay away from their parents. Adult individuals usually do not distinguish their offspring from food, and if they are hungry, they can profit from their own babies.
Other live-bearing fish species
The sharks and rays described by us are cartilaginous fish. Among bone fish, those that breed by spawning are more common. But nevertheless, among them you can meet viviparous. These include cimatogaster. According to some factors, this species of fish is similar to perch fish, and in other ways resembles cyprinids. Their habitat is the Pacific Ocean, its northern part.
But viviparous animals are not only fish whose fry feed directly from the mother in the womb. The female can carry eggs in the abdomen. The fry feed on the yolk. When it comes time to give birth, eggs are formed into fry and the mother begins to throw them. For example, such a method of breeding fish is inherent in the eel. 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 offspring of several hundred thousand. She tosses larvae, each of which is approximately six millimeters.
The only viviparous fish of Baikal
Baikal is a beautiful and deep-sea lake, and it is home to many underwater inhabitants. Among all the diversity here you can find the only live-bearing fish, called the golomyanka. To many, this fact may seem surprising, since usually in the northern latitudes fish reproduce by laying eggs. There are two species of golomyanki. The big one grows up to 25 cm, the small one does not exceed 15 cm. The Golomyanka does not spawn migrations, as happens in other fish that spawn. When the time comes and in the womb of the female, the caviar turns into fry, the mother rises closer to the surface of the water. Most likely, this is necessary for the children to feed on planktonic organisms. The viviparous fish Golomyanka gives a large offspring depending on the species. In small ones, not more than 1.5 thousand fish appear at a time. For large, 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 owners of aquariums know that some of their favorites carry their fry. Basically, live births are inherent in the family of Pecilia, Gudia and some others. Usually these are schooling fish, and they are small in size. Also among them, males are slightly smaller than females, and their coloring seems brighter. When they reach puberty, the male's anal fin becomes gonopodia, through 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 decorative fish, which leads to the appearance of unusual colors and shapes. This mainly concerns guppies. Without selection, a decorative viviparous fish quickly loses its color and gradually degenerates.
Fry development
The development period from eggs to fry in the female’s womb 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 live-bearers of the family of pecillia, young growths are large and much easier than caviar itself, while in other species the weight of fry is much higher than the fertilized eggs. And due to the fact that 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, as the fry immediately show activity after birth. The number of juveniles depends on the type of fish and can be as few as hundreds.
Content of viviparines
In order for the reproduction of viviparous fish to be successful, it is important to take care of their living conditions. Common aquariums in which there are plant thickets are usually suitable for their maintenance. In addition, neutral water requires regular replacement. From 15 to 40% of fluid is replaced weekly. But some species will feel much more comfortable if the water is slightly salted. Such conditions are created mainly for mollies and belonesox. To do this, add a tablespoon of sea salt to ten liters. Also, the ideal water temperature for most species usually ranges from 20 to 25 0 C.
In order for the fish diet to be balanced, they need to add plant components to the feed. This can be a salad, filamentous algae, oatmeal and other foods.