Fish That Lay Eggs; Sharks Information
Shark Birth is Very Interesting!
Scientists today have limited knowledge about shark reproduction, even with today’s techniques and high tech equipment. But, they are studying sharks all the time, trying to find out if they’re more than the ‘eating machines’ they show us that they are.
According to the Florida Museum of Natural History, about 70% of all sharks share a reproduction system that, viewed from a distance, looks very much like that of a mammal. Researchers have found that many sharks give seemingly live births, but they are actually expelling shark babies from eggs that have hatched inside the mother shark.
See, the male shark’s sensory organs attract him and he approaches the female and grabs her with his sharp teeth to hold her in place while he mates with her. As if guided, the male’s clasper finds its way into the female’s upper fallopian tubes where it delivers sperm to fertilize the oocytes (ovum). The fertilized oocytes become embryos and slide into the lower fallopian tubes that form a womb for the embryos.
Of all sharks, 70% (viviparous sharks) actually keep the fertilized eggs inside their body and don’t lay them. The nidamental (or shell) gland forms a material that encases the fertilized ovum in a thin membrane for a shell. The shark pups are protected by the mother’s body for up to 22 months, depending on the species of shark; different types of sharks have a 6 month gestation period.
The remaining 30% of sharks (oviparous sharks) don’t retain the eggs. That nidamental gland forms a hard protective shell around the eggs and then the female lays them in a safe spot. This shark is now finished with her parenting duties, and she will never see the babies that hatch from those eggs.
When the baby sharks are fully developed, the determined shark babies move around the shell until they actually break it open and come out. Oviparous sharks won’t even see this happen, but the Viviparous sharks will expel the pups as if she’s giving live birth to 45-60cm long pups.
Sharks Lay Eggs on the Ocean Bottom
Shark eggs that are laid in the safety of rocks or other protected wedges are about 10-25cm long and contain a large yolk to feed the embryo as it grows. It could take from 6 - 22 months for the shark pups to develop completely inside eggs that are round or oval, depending on the species. One female shark, the Point Jackson shark, actually lays corkscrew-shaped eggs, and she wedges them into the rocks so they get lodged and are not washed away.
All shark pups are born (or hatched) ready for life and they immediately swim away and begin hunting for food. Mother sharks have nothing to do with their offspring, but male sharks in the area will eat the pups.
A shark called the Sandtiger Shark is oviparous, and the first two eggs that are fertilized grow faster than the others, and when they’re developed enough to eat on their own, they turn and eat their sublings in the womb. In the end, only one or two sharks will be ‘born’.
Skates and rays, swell sharks, dogfish and angel sharks all lay eggs that have a very unique shell called a Mermaid’s Purse. It’s a hard, protective rectangular egg casing that has hooks on each end, and they’re sort of shaped like a lady’s purse. These can be found on beaches after a storm or rough seas.
- NewsBBC.co.uk, “Do Sharks Lay Eggs?”, no author or publication date, accessed on 11/17/2010 at 8pm.
- Shark,ch, “Shark Reproduction”, no author or publish date listed, accessed on 11/17/2010 at 7:30pm.
- Florida Museum of Natural History, “Most Commonly Asked Questions”, no author or publish date listed, accessed on 11/17/2010 at 7pm.
- KidZone.ws, “Shark Facts”, no author or publication date listed, accessed on 11/17/2010 at 6pm.
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