Salmon Parents Give Birth to Baby … Trout?

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September 25, 2007

3:47 PM

A breakthrough discovery has been made in the field of conservation biology. Japanese researchers at the Tokyo University of Marine Science and Technology have discovered a way to create fertile trout from salmon.

p. In this method, dubbed “surrogate broodstocking,” researchers inject sterile salmon with spermatagonia, and these cells develop into sperm and eggs, which are used to create wild rainbow trout.
Once the spermatagonia are injected, they migrate toward the fish ovaries or testes and mature into eggs or sperm.

p. It was determined that once the salmon were mature, 10 out of 29 salmon produced milt, which is trout sperm.

p. DNA tests confirmed that the offspring of the salmon were in fact pure trout that were capable of reproduction.

p. University of Tokyo marine bioscientist Goro Yoshizaki started this research with “salmonids,” a family that includes both salmon and trout. He would transfer the sperm into normal fish (non-sterile fish), but this returned hybrids of the two fish that had a high mortality rate.

p. The main interest in this discovery in Japan is its application to conserving bluefin tuna stocks. Earlier tuna conservation efforts, including marine ranching, were too difficult to be commercially viable.

p. It may be possible to produce tuna from mackerel, which would be much more cost and space effective. A mackerel’s body size is around 500 to 1,000 grams, which is close to 1,000 times smaller than a tuna’s body size, making it much easier to culture and grow.

p. Earlier efforts to preserve endangered fish have proven lofty. Such methods include freezing fertilized eggs, which is impossible because of the size and fat content of fish eggs.

p. In a project headed up by zoology professor Joseph Cloud and funded by the U.S. government, the University of Idaho is now trying to assess the viability of this technology for culturing endangered fish stocks.

p. Scientists at Idaho will use trout, a species more plentiful than salmon, to produce the endangered sockeye salmon.

p. Many scientists, like John Wadman, a fisheries biologist at Queen’s College, feel that this type of fish rearing can be highly beneficial to bolstering the world’s fisheries’ stocks.

p. “Future work should look to expand this approach to other fishes in need of conservation, in particular, the sturgeons and paddlefish. We have a lot of species of fish around the world that are really in danger of becoming extinct,” Wadman said in an interview with the Associated Press.

p. Results similar to those obtained in the salmon-trout study were also found when injecting trout spermatagonia into other fish species like brown trout and Japanese char.

p. This implies that there may be a wide range of fish that can be created from other fish, which is a monumental discovery for restoration efforts.

p. Efforts like those at the University of Tokyo and the University of Idaho demonstrate the growing importance of alternative methods of conservation.

p. While limits on harvesting will still be imposed in an effort to minimize overharvesting, research into alternative ways of repleting fish stocks is an important step in restocking the Earth’s waters.

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