New research has revealed that half of the world’s farmed salmon have hearing loss, stemming from an ear bone deformity. Not only does producing farmed animals with deformities go against at least two of the "Five Freedoms" of farmed animal welfare -- freedom from pain, injury, or disease, and freedom to express normal behavior -- but this discovery is eye-opening with regards to the failure of most current wild salmon conservation programs, which have their root in farmed salmon.
The Farmed Salmon Study Results
The study, published in the journal Scientific Reports and was led by researchers from the University of Melbourne, tested farmed Atlantic salmon from the world’s major salmon producing nations – Norway, Canada, Scotland, Chile, and Australia – and found that more than half of the world’s farmed Atlantic salmon had this deformity, over 10 times more than wild fish.
The fish were not born with these deformities, the researchers noted. "The deformity occurs when the typical structure of calcium carbonate in the fish earbone is replaced with a different crystal form," Tormey Reimer, lead author on the study, told Science Daily. "The deformed earbones are larger, lighter and more brittle, and the way they perform within the ear changes."
The deformity of the bone, called the otolith, is similar to deformities of the inner ear bone in mammals; it affects the fish’s balance and ability to situate itself in space, not to mention its hearing.
What Does This Mean?
Conservation efforts for farmed salmon have long been relatively fruitless, and researchers now believe that this may be the cause, according to study co-author Associate Professor Tim Dempster from the School of Biosciences, University of Melbourne.
Billions of captive-bred juvenile salmon are released into North American rivers every year, and their survival rate is 10 to 20 times lower than that of wild salmon. Researchers now postulate that their low survival rate may be due to their inability to detect predators or to navigate back to their home stream, a problem linked to this ear bone deformity.
This is a huge discovery when it comes to the future of both farmed and semi-wild stocks of salmon. Eighty-five percent of the world’s current marine stocks are either fully exploited or overfished, meaning that the success of these conservation programs is vital to the survival of these species on the whole, not to mention the continued sustainable consumption of wild and farmed salmon.
“All native fish re-stocking programs should now assess if their fish have deformed earbones and what effect this has on their survival rates,” said study co-author Steve Swearer.
The Future of Farmed Fish
Salmon farming is a 40-year-old industry, with more than one billion farmed salmon harvested every year. This industry must make big changes to accommodate this new information.
“We now need to work out what is the root cause to help the global salmon industry produce fish with acceptable welfare standards,” said Dempster. As the problem is irreversible, only once the root cause of this deformity is found can a solution be posited.
Salmon run image via Shutterstock