Sharks are truly fascinating animals. They also become strangers the more we learn about them. You may already be aware of facts like the fact that some species of animals give birth to live young and that some female sharks have both a left and a right uterus. You may be surprised to learn that shark fetuses can swim from one uterus to the next. They are also fairly quick at it.

Sonograms of pregnant tawny nurse sharks performed at the Okinawa Churaumi Aquarium in Japan were shown to have accomplished the amazing accomplishment, according to a report in the journal Ethology. Although the researchers’ explanation is horrifying, there is no obvious explanation. Some shark species nourish their fetuses through oophagy, which means the unborn young sharks consume eggs while still in the womb, occasionally even their siblings. A better survival likelihood can depend on the capacity to search for additional eggs.

We haven’t seen mammals behave in the uterus like this. While the fetuses of mammals are largely motionless, the young sharks can swim up to 8 centimeters (3.1 inches) every second. The study, which lasted for several years, concentrated on three tawny nurse sharks that were expecting. A total of 40 ultrasound clips were gathered by the researchers, demonstrating both the real movements and the range of situations that emerged inside the womb. One mother’s embryos switched sides three times, while the offspring of another mother did so 24 times. The researchers even saw a pregnancy with only one (well-fed) pup instead of the usual two in each uterus.

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In addition, the team found that tawny nurse sharks occasionally open their cervixes, allowing their pups to stick their snouts outside the uterus if they choose to. When compared to pregnancy in mammals, this is significantly different. Mammalian pregnant females have a tightly closed cervix until giving birth.

The development of underwater ultrasonography was essential to making this study possible. The animal tank provided a less stressful environment for this gadget to enable the observation of the pregnancy. For previous observations, the shark had to be physically removed from the water, which is not the best setting for observing “regular behavior.” The device must endure the pressure at the bottom of the tank and be waterproof for it to function. The upgraded ultrasound is a prerequisite for the underwater OB-GYN and will enable even more fascinating experiments.

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