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article imageShark Pregnant in Aquarium With No Males

By Tea Lulic     Jun 25, 2007 in Science
Veterinarian Bob George sliced a dead shark open and saw something he thought was impossible. Shutting his eyes for a second to think about what he has seen, he opened them again - and they weren't lying. A female shark was carrying a pup - but how?
When sharks die from an unknown cause, veterinarians have a tendency to open them up and search for a reason of their death just in case they were not carrying a disease which could be spread onto other fish.
While cutting open the shark, George saw the outline of a fish. No surprise there since sharks eat fish and digest their food slowly. But then he realized that he wasn't looking at Tidbit's (shark's name) stomach but her uterus. In it, he found a perfectly formed, 10-inch-long shark pup that was almost ready to be born.
Initially, he he wanted to know why Tidbit reacted badly to routine sedatives during a physical and died hours later after it bit an aquarium curator on the shin.
Now, George was not yet dumbfounded. But when he realized that there were no male Blacktip Reef sharks at the Virginia Aquarium & Marine Science Center in Virginia Beach, he was shocked. Sharks only mate with the same species so there was no possibility for Tidbit to get pregnant.
But, there are possibilities: could it be that Tidbit conceived without a male? Could it be that she was one of the shark hybrids?
The first case of asexual reproduction amongst the sharks was reported at Nebraska zoo where a pup was born and an egg developed in a female without a sperm from a male.
One of the scientists who worked on the above mentioned study contacted the aquarium, which in turn sent him tissue samples from Tidbit and her pup for testing. If the pup's DNA contains no contribution from a male shark, this would be the second known case of shark hybrids.
George will receive preliminary results soon but conclusive results will take months.
History of Tidbit
Tidbit has lived in an aquarium for 10 years and it has swam with the other sharks in a 300,000-gallon tank. Since sharks get yearly check-ups, Tidbit was guided into a smaller corral to be examined out of public view.
Every Balcktip Reef shark is sedated because they are sensitive to change. With a mixture (they suppose) of sedatives, unknown pregnancy, stress of being transported and bitten by another shark, Tidbit went into a sedation deeply.
Two veterinarians, George and Beth Firchau massaged her tail to get her blood flowing and then gave her a stimulant to help her breathe. However, this made the shark uneasy.
It swam away, bumped into a wall and then headed back towards Firchau at which point it clamped onto her left shin. Veterinarians were not sure whether Tidbit meant to attack Firchau or whether it just collided with her and then snapped reflexively.
Firchau did not react right away but thought of shark's behaviour as "weird." She was later taken to a hospital where she received stitches.
George and the rest of the team tried to revive the shark. Tidbit rallied a couple of times but then died 12 hours later.
At first, George was depressed by the events, but after he found out that Tidbit was pregnant he was kind of glad. He explained that if Tidbit did have a baby at the aquarium and the employees did not know about her pregnancy, the pup would have been eaten by other sharks.
Now, George and his team are puzzled by her pregnancy, calling it a mystery, for now at least.
Sharks usually mate before being able to conceive. Their egg is fertilized by sperm, which then produces an embryo that contains a set of chromosomes, half of which came from the mother and half from the father.
In asexual reproduction, an egg splits in two. The DNA is contributed from the mother's doubles, so each egg has a full set of chromosomes coming from a mother. The eggs then fuse and make up an embryo without the sperm from a male.
The study which investigated the possibility of sharks asexually reproducing, proved that when there is no other way to reproduce, nature will find an alternative way to let this occur. This means that asexual reproduction in sharks might be more common than we think - of course, only if they're in captivity.
If you think that Tidbit got impregnated by another male from a tank, the possibility of this is zero. Crossbreeding is not known to happen among sharks at all.
It's not natural," Thomas aquarist at the John G. Shedd Aquarium in Chicago said. "If you've got a shark that needs to swim to breathe and cross it with a shark that can lay on the bottom to breathe, what are you going to get? Are you going to get these weird mutations?"
Even though it would be interesting to find out that Tidbit is a shark hybrid, George hopes that it got impregnated by crossbreeding. He stated that if one thinks logically, crossbreeding would make perfect sense.
This just shows how animals are able to adapt to the environment. Even though the evolution did not create asexual reproducing sharks, the nature has definitively taken its course in this case. However, before jumping to conclusions and being amazed, we should wait for the results.
More about Shark, Hybrid, Unknown
 
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