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Half of farmed salmon have poor hearing

Half of farmed salmon have poor hearing

A study undertaken by the University of Melbourne has discovered that there is a global phenomenon of farmed salmon with deformed ear-bones (‘otoliths’). This bone is described as being essential for the salmon’s hearing and balance – the equivalent of the inner ear for humans. The bone is also key to a salmon’s sense of navigation.

The study, published in the journal Scientific Reports, found that half of the world’s farmed Atlantic salmon have the deformity, and as a result, poor hearing. This brings about fresh concerns over the farmed salmon that make their way into the wild aquaculture each year (by various means), going on to breed with wild fish. The deformity is extremely uncommon in wild fish.

Tormey Reimer, from the University of Melbourne’s School of Bio Sciences, led the study. Summing up the discoveries of their work, she said: “Farmed fish are 10 times more likely to have the earbone deformity than wild fish.”

“It [the deformity] occurs at an early age, most often when fish are in a hatchery, but its effects on hearing become increasingly more severe as the fish age. Our research suggests that fish afflicted with this deformity can lose up to 50 per cent of their hearing sensitivity.”

The research included the sampling of salmon from across the world – including Norway, Canada, Scotland, Chile and Australia. The occurrence of the deformity occurred at much higher rates in farmed salmon compared to their wild counterparts.

Associate Professor Tim Dempster, co-author of the study, commented on the deformity, saying; “Something about the farming process is causing the deformity.”

“We now need to work out what is the root cause to help the global salmon industry produce fish with acceptable welfare standards.”

It is estimated by those who carried out the study that around half of the one billion salmon harvested from farms each year carry this deformity, and thus have “compromised hearing.”

Ms Reimer said: “Producing farmed animals with deformities contravenes two of the Five Freedoms that form the basis of legislation to ensure the welfare of farmed animals in many countries.”

Professor Steve Swearer, a co-author of the study, commented on what fish farms should now do, in light of this new research, saying: “All native fish re-stocking programs should now assess if their fish have deformed ear-bones and what effect this has on their survival rates.

“If we don’t change the way fish are produced for release, we may just be throwing money and resources into the sea.”

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