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A lot of people get confused and think sharks are mammals because they compare them to dolphins, which are. However, I must highlight that sharks are not mammalian animals; they actually belong to the group of fish. They only have a certain characteristic in common with mammals; that is, they are vertebrates, even though they have a cartilaginous skeleton.
When I talk about the cartilaginous skeleton, I mean that it is not made from bones, but from slightly softer tissue, very similar to the bone structure of mammals. Another visible difference between mammals and sharks is that they do not have breasts to feed their young.
Sharks are viviparous animals, which means that their growth and development take place inside the mother’s body, but this doesn’t mean that the babies are gestated like the mammal ones. Sharks, instead of laying eggs, incubate them inside them until they are hatched. Although I must emphasize that there are some exceptions.
Reproduction in sharks
The first thing to remember is that although sharks are generally viviparous, there are some species that are oviparous or ovoviviparous, so their modes of reproduction may be slightly different from each other. This is one of the characteristics of sharks that makes them unique.
How do sharks reproduce and how are they born?
- Oviparous reproduction: This type of reproduction is based on the female who lays her eggs in a certain area of her habitat once they have been fertilized by the male. Fertilization in sharks is internal, meaning that the reproductive organs of both parents unite, as is the case with mammals.
- Ovoviviparous reproduction: This type of reproduction is very particular because the female, instead of laying her eggs in a protected place, keeps them inside the body as long as it is necessary for further hatching. In this case, the shark baby will develop and feed on the nutrients provided by its own egg. When the hatching takes place inside the mother, at that time, the babies will begin to feed on those eggs that have not been fertilized by the male. When their reserves run out, it is the ideal time for the pups to leave the mother’s body.
- Viviparous reproduction: The viviparous are peculiar because although they also begin to develop in an egg inside the mother, when it ceases to provide the necessary nutrients, they will hatch and be covered by a bag very similar to the mammalian placenta. This bag will be the carrier of new and necessary nutrients that the offspring need to complete their development.
As we have already seen, although the breeding and development of sharks have some characteristics similar to those of mammals, they are actually different. This is why we must not confuse these creatures with mammals.
How do sharks lay eggs?
As mentioned before, regardless of how the birth and the different stages of the development of a shark, they are born from an egg, because without the existence of one, there would be no fertilization, development, or progeny. For this reason, eggs are essential in the reproduction of these animals.
Although we are talking about eggs, shark eggs are completely different from the eggs of birds, reptiles, or other fish, because they have certain characteristics that differentiate them from all of them.
In the case of oviparous sharks, they have an encapsulated appearance. Besides this, they have some kind of hooks that will help them adhere to surfaces, whether they are rocky, coral, or seaweed. There are some species whose eggs can be compared to a large wick tip because of their spiral shape. This will help the egg to have good adhesion to the surface where it will remain anchored until hatching.
The appearance of the eggs will depend on the species of shark and how it will spend its time before the baby is born. For this reason, there is a wide variety of models that are particularly distinguished due to the different shapes they present.
On some beaches around the world, we can find naked shark eggs. They usually have a much elongated and cylindrical shape; their color is almost transparent and they are usually more or less large in size. These bags of eggs are known by some people as “mermaid bags” because of their shape and due to the fact that in many mythological drawings or stories with mermaids, they are used as bags.
Is it fair to call baby sharks pups?
Yes, sharks that have just been born can be called pups. After learning about the breeding and birth of shark pups, we can also add that they are born fully developed and ready to live independently.
Fish can also be called pups from the moment of birth until they reach the stage where they can be active in reproduction. Therefore, the term “rearing” can also be used in these marine animals. However, we must remember that once they reach adulthood, they will no longer be called pups and should bear the name sharks.
Is there cannibalism among sharks?
The answer to this question is yes. In some cases, and species of sharks, like the descendants of ovoviviparous sharks, when all the nutrients supplied by their own egg are finished, they come out of it and begin to eat the other eggs that still remain inside the mother, regardless of whether they have their brothers inside. In fact, they prefer to eat their brothers, because it provides them with a lot more nutrients.
This type of cannibalism is known as “intrauterine cannibalism” and can occur in several animal species. It’s not very common to see, but it’s something that’s happening and that we need to be aware of, especially in tiger sharks. The female of this species usually has much more eggs inside her than other sharks, because she has two wombs inside her body. In the end, only two babies will be born, one from each uterus, the ones who will be the survivors.
Although it seems cruel, it is part of the nature of these animals. They must learn to survive at a very young age, and the first test they must pass is to survive in order to be born. So, in order to feed themselves, these animals will end up eating all the other eggs that are inside their mother, whether or not they are fertilized. This action is known as cannibalism.
In captivity, some shark females were able to reproduce asexually, meaning without the need for a male. Apparently, in the absence of a male to fertilize them, the females have developed mechanisms to ensure survival in extreme conditions, which offers us an idea of how strong the instinct of these fish is.