Deaf Fish

A recent study shows that every second farmed salmon we eat is deaf resulting of a deformity in the ear, caused by accelerated growth in aquaculture. The study’s lead author, Ms Tormey Reimer, says when they went looking for the cause of the deformity they found that the fastest-growing fish were three times more likely to be afflicted than the slowest. “We also found that we could reduce the incidence of the deformity by reducing how fast a fish grew. Such a clear result was unprecedented,” says Ms Tormey, a masters graduate from the School of BioSciences at the University of Melbourne.

The deformity occurs in the otoliths, tiny crystals in a fish’s inner ear that detect sound, much like the ear bones in humans. So even a small change can cause massive hearing problems. Normal otoliths are made of the mineral aragonite, but deformed otoliths are partly made of vaterite which is lighter, larger, and less stable. The team found that vaterite was seemingly caused by a combination of genetics, diet and exposure to extended daylight (since fish only eat and grow during the day, many farms expose their stock to bright lights 24 hours a day). However, there was one factor that linked them all: growth rate. As in people and farm animals, growing fast often means growing too fast. Small is not only more beautiful, it also hears better.

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