Farmed salmon should be sterilised to prevent any risk of them breeding with wild fish and introducing genetic weaknesses, experts have urged.
New research shows that while salmon bred in captivity for food consumption are genetically different from their wild relatives, they are just as fertile, potentially damaging wild populations if they escape and breed with them.
Millions of salmon escape from fish farms each year, and can get into wild spawning populations, where they can reproduce and introduce negative genetic traits, the researchers claimed.
Recently escaped salmon are not as good at reproducing as wild fish, but the research shows that their sperm and eggs are as potent as those of wild salmon.
If farmed salmon can revive their spawning behaviour by a period in the wild, they could breed with wild populations, the researchers argued.
Lead researcher Professor Matt Gage, from East Anglia University’s School of Biological Sciences, said: “Around 95% of all salmon in existence are farmed, and domestication has made them very different to wild populations, each of which is locally adapted to its own river system.
“Farmed salmon grow very fast, are aggressive, and not as clever as wild salmon when it comes to dealing with predators.
“These domestic traits are good for producing fish for the table, but not for the stability of wild populations. The problem is that farmed salmon can escape each year in their millions, getting into wild spawning populations, where they can then reproduce and erode wild-gene pools.”
But Scottish Salmon Producers’ Organisation chief executive Scott Landsburgh hit back at the claims. He said: “The survival rate of farmed salmon in the wild is virtually zero. There is no evidence that escaped fish have created any actual problems whatsoever for wild salmon. All the supposed threats are theoretical, and unfounded.”
He added that the industry made “huge efforts” to improve containment.
Researchers used a series of in vitro fertilisation tests in conditions that mimicked spawning in the wild. All tests on sperm and eggs showed the farmed salmon were as fertile as wild salmon, identifying a clear threat that they could breed with wild populations.
Prof Gage said a viable solution was to induce a condition called “triploidy” by pressure-treating salmon eggs just after fertilisation, making most of them infertile.
My Landsburgh dismissed the solution.
He said: “The possibility of using triploid stocks has been under consideration for some time. However, projects set up to look at its viability continue to return serious questions in terms of fish welfare implications and economic viability.”