Special Sub-Topic: Live Shark Reproduction Authored by: Flynn_17 Sub-topic of: Fish

When a shark gives birth to live young, it is described as 'viviparous' or 'ovoviviparous'. What is the name given to these live young, though?

Pups. External egg development is sharks in known as 'oviparous', as the young sharks are born outside of the mother. Small to medium sized sharks, such as Port Jackson and leopard sharks use this method.

Which of the following descriptions best fits the term 'ovoviviparous'?

The shark carries eggs within its body until they hatch. Later, the young are expelled as live sharks.. 'Ovovivaparity' is often called 'aplacental vivaparity', as although the embryos are held inside the mother, a placenta does not form. While inside the mother's uterus, the young sharks feed on the eggs still being produced by the mother. Makos and threshers are known to use this method, which is known as 'oophagy'

None of the ovoviviparous sharks are embryophagous, which means none of them will eat their brothers and sisters while they are still in the uterus.

f. While most ovoviviparous sharks are oophagous, the sand tiger shark will eat its brothers and sisters in the uterus before it settles down and eats the eggs the mother provides.

If a shark uses a viviparous method of raising its young, then a placenta is formed, and the young shark develops within the mother as a mammal would. It is fed by a placenta and an umbilical cord, and when born, the cord is cut by the mother. Which of these sharks is NOT known to be viviparous?

Great white shark. All hammerhead sharks, and most 'sharpnose' sharks, are viviparous. Viviparous sharks can have, on average, between two and twenty pups. The typical amount for lemon sharks and hammerheads is 15-17 young born at a time.

Sharks normally give birth to their young tail first, but some species prefer to give birth to their young head first. Why does the hammerhead shark prefer this method?

The 'tee-shaped' head of the young are soft and pliable, and will bend to allow an easy exit when born head first.. Another shark that also gives birth to its young head first is the sand tiger shark.

Most sharks will only give birth every other year to conserve nutrients, but viviparous sharks give birth to young every year.

t. Viviparous sharks such as hammerheads and lemon sharks do not need to store nutrients (due to the placental nature), and neither do the egg-laying, or oviparous sharks. Oviparous sharks will also lay eggs every year.

Female sharks are often found with marks and scars around their reproductive organs. This has to do with the mating process. What do the males do when mating with the females to cause this scarring?

Males bite and clasp the females. Males have 'claspers', which are cartilage spikes hardened by calcium. These are used to maintain a grip on the females during reproduction. A male also bites the female's fins and flanks until she is receptive.

Both males and females have reproductive organs. The male has two testes, and the female has a uterus with two ovaries. In the male, the left testicle is often much smaller than the right, and is not as efficient. In the female, one ovary is also smaller and less efficient. But which one?

left&left ovary&L. The uterus and ovaries are found within a cloacal cavity on the underside of the female shark. Males also have a cloacal cavity, but have 'claspers', making it easy to tell the different between a male and a female shark.

Where would 'appendicula' be found on a pregnant female viviparous shark?

On the umbilical cord. Appendicula are small projections on the umbilical cord which give the cord a larger surface area for getting rid of waste and absorbing nutrients.

Only primitive sharks give birth to live young.

f. In fact, only very well evolved sharks give birth to live young. The primitive sharks are mainly oviparous, and lay eggs on the ocean floor, or in coral. Examples of primitive sharks include dogfish and angel sharks.