Salmon in farms have hearing deformity
HALF of the world’s farmed Atlantic salmon have hearing loss which could be compromising critical restocking programmes, according to new research.
The report published in the journal has revealed for the first time that the farmed salmon are 10 times more likely than fish in the wild to suffer from a deformity of the earbone thought to be leading to the hearing loss.
The salmon’s ears are essential for hearing and balance, so the findings are significant for the welfare of farmed fish as well as the survival of captive-bred fish released into the wild for conservation purposes.
The University of Melbourne-led study found that half of the world’s most farmed marine fish, Atlantic salmon, have a deformity of the otolith or ‘fish earbone’, much like the inner ear of mammals. The deformity was found to be very uncommon in wild fish.
Tormey Reimer, lead author of the University of Melbourne-led study, said: “The deformity occurs when the typical structure of calcium carbonate in the fish earbone is replaced with a different crystal form.
The deformed earbones are larger, lighter and more brittle, and the way they perform within the ear changes.”
“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,” she added.
Deformed earbones could also explain why many fish conservation programs are not performing as expected.
Hearing loss may prevent fish from detecting predators, and restrict their ability to navigate back to their home stream to breed.