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   Scientists to breed test-tube sharks

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Topic: Scientists to breed test-tube sharks (Read 153 times)

Rhune
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Scientists to breed test-tube sharks
« on: Jul 28^th, 2005, 8:49pm »

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Scientists to breed test-tube sharks

Thursday, July 28, 2005; Posted: 11:09 a.m. EDT (15:09 GMT)

SYDNEY, Australia (Reuters) -- The endangered grey nurse shark is its own worst enemy, its young eat each other in the womb, so Australian scientists have a radical rescue plan to artificially inseminate and breed the ocean predator in test-tubes.

The grey nurse is one of the fiercest-looking but most docile marine creatures, and despite it being declared endangered in 1984 and its habitat protected, it could become extinct along Australia's east coast within 20 years, scientists say.

In a process called intra-uterine cannibalism, grey nurse embryo pups develop a jaw and razor-sharp teeth very early in their development and cannibalize siblings in the womb.

The sharks have two wombs in which a dominant pup will consume its siblings, leaving only two surviving pups every two years when the shark breeds.

"It is not breeding quickly enough. It is being caught out in the wild and it is not recovering from the fishing pressures on the east coast," said Melbourne Aquarium curator Nick Kirby.

Nicknamed the "labrador of the sea" due to its docile nature, grey nurse numbers plunged after being wrongfully blamed for many attacks on swimmers off Sydney beaches and it was brutally hunted until the 1960s.

Their plight has now become critical.

Breeding programs have been used to conserve the endangered cod trout in Australia, the Mexican grey wolf and Californian condor, but scientists here say this will be the first attempt at shark breeding.

Melbourne Aquarium this month artificially inseminated Lonnie, a 2.6 meter (8.5 feet), seven gill shark with the sperm from a male tank mate.

It will take several months to see the first signs of any pregnancy, but if successful the insemination technique could be used on the critically endangered grey nurse.

"We are using our seven gill shark as a surrogate species because they are more common and easier to work with than risking the grey nurse shark," Kirby told Reuters.

A common problem trying to breed sharks in aquariums is their reluctance to mate. No seven gill sharks have been born in captivity in Australia and only eight grey nurse pups have been born in Australian aquariums in the past decade.

To inseminate Lonnie, scientists had to first use ultrasound to determine the female shark was ovulating and then sedate a seven-gill male shark, named Gonzo, and internally massage its guts to stimulate the production of sperm, which was then injected into Lonnie's reproductive tract.

"We expect in two or three months to do an ultrasound to check the embryos and eggs development," said Kirby. "After fertilization we are talking a year for pups to be born and with seven gills there could be 60 or more pups."

Artificially inseminating grey nurse sharks will not avoid intra-uterine cannibalism, so marine scientists at the New South Wales (NSW) state fisheries department have come up with a radical plan to breed the embryo sharks in individual test tubes.

"Once the embryos have developed to a certain size (10 cm) they actually have a fully functional set of jaws and teeth, then they swim around and cannibalize their siblings," said fisheries marine biologist Nick Otway.

"We have to bypass this cannibalistic phase. Once the animal gets through that stage it fends for itself. It just swims around the womb eating, we just have to feed it," Otway said.

With only one embryo pup surviving in each womb, the female shark then produces unfertilized eggs for it to feed on until it grows to about one meter (three feet) in length and is born. Each pup consumes an estimated 17,000 pea-sized unfertilized eggs.

Scientists plan to harvest embryos from pregnant female grey nurse sharks in the wild, then raise them in specially built artificial uteri in fisheries laboratories.

The government funded shark test-tube plan has a 10-year timeframe as scientists must first learn how to create an artificial shark uterus and develop artificial uterine fluids and artificial eggs to feed the shark pups.

Once built, the artificial uteri will be tested with embryos from non aggressive sharks so as not to risk grey nurse sharks.

Scientists will then develop the surgical procedures to harvest embryos from female sharks in the wild and insert the embryos into the artificial uteri.

Grey nurse (Carchatias taurus) numbers are declining worldwide, with populations off South Africa, the U.S. east coast, South America, Japan and New Zealand.

Otway believes current tagging techniques to keep track of grey nurse sharks will be used to help harvest embryos.

Identity tags will tell scientists which female sharks are likely to be pregnant, they will then be caught in a plastic float and ultrasound checked to confirm pregnancy.

If they are pregnant they will be lifted into a tank onboard a ship and flipped onto their backs, which causes tonic immobility, or catalepsy, just as it does in chickens, enabling embryos to be either flushed out or extracted with forceps.

Unlike other sharks which must be constantly moving forward to force oxygen-enriched sea water through their gills, grey nurse sharks can pump the water through gills enabling them to remain stationary. This will help scientists keep them in a fixed position while extracting embryos, and if necessary, to administer a sedative over their gills.

Once inserted into the artificial wombs the embryos will be fed artificial shark eggs until they reach birth size and then released into the wild.

"If we do not do this the animal is going down the gurgler (drain)," said Otway. "This animal will not survive on the east coast of Australia unless we can do this."

Copyright 2005 Reuters.

« Last Edit: Jul 28^th, 2005, 8:50pm by Rhune »

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