28-Oct-2009
New technology uses hormones to enable the endangered fish to breed in captivity.

It was ‘80s band REO Speedwagon who insisted on its album cover that “You Can Tune a Piano, but you can’t Tuna Fish.” But recently, marine scientists around the world have been proving the rockers wrong—they’re “tuning” bluefin tunas’ biology, implanting hormones into the endangered fish to spur them to reproduce in captivity.
 
”It’s like OB-GYN for fish,” says Yonathan Zohar, director of the Center of Marine Biotechnology at the University of Maryland’s Biotechnology Institute.
 
Last month, researchers from Germany’s Heinrich Heine University used spearguns to deliver reproductive hormones to caged bluefins off Italy; within days, the fish spawned millions of fertilized eggs. The team is the latest to join a growing number of scientists and aquaculture farms around the world who are using such methods to get captive fish to breed—something that’s proved tricky in the past.
 
While breeding bluefins in captivity is controversial among both environmentalists and scientists, advocates say it’s an important step toward conserving the suffering swimmers. Bluefin populations have dropped by as much as 90 percent in some areas due to overfishing and the global demand for sushi.
 
“If we can develop bluefin tuna through marine aquaculture, this will definitely ease pressures on bluefin tuna in the wild,” says Zohar, who led the first successful hormone implantation project in bluefin tuna in July of 2005. “I expect it [hormone implantation] to be increasingly used and expanded for bluefin tuna as the hatchery technologies for this species are developed.”
 
Keeping tuna in tanks and cages complicates reproduction—the massive fish are extremely active and typically migrate great distances, so simulating their natural environment is nearly impossible. Zohar and colleagues hypothesized that when the fish are in captivity, a key hormone used in bluefin reproduction, gonadotroptin-releasing hormone (GnRH), isn’t produced or malfunctions. So the researchers created a synthetic version of GnRH, inserted it in a biodegradable device that slowly releases the substance over a period of time, and implanted it into adult bluefin.
 
The technique succeeds in getting tuna to produce fertilized eggs. “The [implants] result in spawning and production of juveniles that will be used both for aquaculture for food consumption as well as potentially to be released to the wild for stock enhancement,” Zohar says. The technology is now used in facilities and labs around the world.
 
Still, some scientists are fearful that the method will hurt the world’s oceans more than it will help.
 
“We’ve seen all of the problems associated with farm-raising salmon, and there’s no question in my mind that the problems with bluefin tuna are just as large,” says Michael Hirshfield, chief scientist at Oceana. Especially worrisome, says Hirschfield, is the practice of catching other small fish to feed to captive bluefin tuna. “Those fish are no longer available to other predators—seabirds, marine mammals, whales,” he says. “We’re essentially robbing the ocean ecosystem of key food items for other species and diverting them to bluefin tuna.”
 
Another concern is that farmed tuna released into the ocean to bolster populations will act differently than their wild counterparts. Other experts think that while farming tuna can be a worthwhile way of reducing pressure on wild populations, it can also distract the public from the need to decrease overfishing.
 
Whatever their stances, critics and supporters of bluefin tuna farming agree that immediate action is imperative to save wild stocks from collapse. What that action is—and whether it’s even possible—is debatable.
 
“I believe there are big opportunities, and I think sustainable aquaculture is the future so that we can take the pressure off wild stocks,” says Barbara Block, a marine scientist at Stanford University and Monterey Bay Aquarium. “But note the word ‘sustainable’—that your output into the world’s oceans is clean, that you’re not taking too much from the sea to feed tunas in the land-based facilities or pens. Many question whether it can be done.”
 
And some, like Zohar, believe the best bet for conserving bluefin tuna is employing multiple strategies.
 
“Everything that we do to preserve a species requires a toolbox, and this toolbox has several tools in it,” says Zohar. “Obviously regulating fishing and reducing the harvest is a very important tool in that box. Another very important tool is developing bluefin tuna aquaculture. Those tools are completely synergistic, and it’s to be used together for a quicker recovery.”
 
Story by Sarah Parsons. This article originally appeared in "Plenty" in August 2008.
By PlentyMag.com
Tue, Mar 24 2009 at 12:42 PM EST
Copyright Environ Press 2008

To listen to Cyndi's radio interview on the ABC as to why propagated fish aren't as nutritious, use the following link: http://blogs.abc.net.au/sa/2009/10/regaining-lost-tuna.html#more

More news