Scientists breed trout out of salmon

Scientists have managed to breed trout from salmon using a new technique they hope will allow them to create tuna fish from mackerel.

The Japanese researchers hope to produce stocks of valuable, endangered species by injecting their germ cells into sterilised embryos from other species.

Goro Yoshizaki, a marine biologist, from the Tokyo University of Marine Science and Technology, Japan, used the method to successfully breed trout from salmon.

The embryos they produced developed into adult trout of both sexes, capable of producing either trout sperm or eggs. These were then combined to produce healthy trout offspring.

The scientists say the technique could be used to preserve threatened species if traditional methods such as reducing fishing, breeding in captivity or restoring their habitat fail.

However the real target of the work is the bluefin tuna -- an important ingredient in Japanese sushi and sashimi.

European Union officials last week banned member countries from fishing for bluefin tuna in the eastern Atlantic and Mediterranean for the rest of the year because fishermen had caught their annual quota early.

Mr Yoshizaki said: "If we can transplant tuna germ cells into small mackerel which mature when they reach about 600g -- 1,000 times smaller than that of tuna -- they can produce tuna eggs and sperm. Consequently, by mating male and female mackerel, we can obtain tuna fertilised eggs in small fish tanks. By this way, we can save a lot of space, labour, and cost.

"There are a lot of fish species or populations facing extinction because of environment destruction and over-harvesting. Obviously environmental protection and [halting] fishing is the best solution, but we need some backup system to conserve endangered species."

Of 29 sterile masu salmon embryos injected with rainbow trout germs cells, 10 grew up to be adult salmon capable of producing trout sperm 17 months later. When the germ cells were transplanted into female salmon embryos, five of the 50 resulting females could produce viable trout eggs. Mr Yoshizaki then used the salmon-produced sperm to fertilise the salmon-produced eggs. Almost nine out of 10 of the fertilised eggs produced healthy trout.

Jean-Christophe Vie, the deputy head of the World Conservation Union's species programme, warned that the technique would not help species that are threatened because of changes to their natural habitat.

"It's naive to think that it will be enough to reproduce a species and throw it back into nature and the species is saved. For a species to survive, it needs to be adapted to its environment."

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Scientists breed trout out of salmon