14 DAY TRIAL // We do not know when women will start to bear chimp offspring to save their species, but a Japanese team has already obtained trout from salmon parents. This could be crucial for saving many endangered species of fish.
The team inserted germ cells (precursors to sperm and egg cells) from male trout (sperm precursor cells are called spermatogonia) into sterile salmon embryos. The embryos grew into adult fish of both sexes, some fertile and producing either trout sperm or trout eggs. When these sperms and eggs were combined, they produced healthy trout individuals. In nature, trout and salmon will never interbreed.
The new method could be the last hope for species threatened by habitat loss and which cannot be bred in captivity. By now, the germ cells have been kept frozen in liquid nitrogen for up to 10 months, but "theoretically, they are stable forever," said lead researcher Goro Yoshizaki of the Tokyo University of Marine Science and Technology in Japan.
The spermatogonia came from male rainbow trout and were injected into sterile masu salmon embryos. 10 of 29 male embryos delivered adult salmon producing trout sperm about 17 months later. The spermatogonia inserted into female salmon embryos made 5 of the 50 resulting females to deliver viable trout eggs. Previously, this experiment was made with trout germ cells and trout embryos.
When the team fertilized the salmon-produced eggs with salmon-produced sperms, about 89% of the eggs delivered healthy trout. The researchers tracked down the trout DNA with a green fluorescent protein. The hatchling trout had the fluorescent protein, thus they had developed from the trout germ cells.
"If this can help save a few species, why not?" says Jean-Christophe Vi?, deputy head of the World conservation Union's species program.
"Most threatened species are not disappearing because they cannot reproduce, but rather because of changes to their natural habitat that make survival difficult. 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," Vi? told New Scientist.
"For a species to survive, it needs to be adapted to its environment. Species that have already become extinct in the wild are even less likely to survive if they are brought back through artificial reproduction. There is just one condition for a species to flourish - and that's for the threats that it suffers from to cease."
The Japanese team is collaborating with Penny Swanson of the Northwest Fisheries Science Centre, a federal research institute in Washington state, US, in an attempt to repeat this deed with germ cells coming from the endangered sockeye salmon. Salmon and trout are closely related, belonging to the same genus from the Salmonide family, that's why the technique could not work with more divergent species.
"I do not think salmon can produce tuna eggs or carp eggs," Yoshizaki told New Scientist.
Still, it could be useful in helping the survival of some endangered species of fish.
"Germ cell banks could operate much like a seed banks, which store seeds from different plant species." said Bryan Clarke, head of The Frozen Ark, a group looking to gather genetic material from threatened species.
Still, "More effort should be put into protecting living species in the first place. Let's protect the genes, but let's protect them alive." said Vi?.