To grasp the wide-ranging impacts of our industrial food systems, take a peek inside a salmon’s ear. That’s what marine biologist Tormey Reimer did when, in 2013 at the University of Melbourne, she began to investigate deformities that were developing on the structures that salmon use to hear.
Bony fish species have structures called otoliths in their ears, small crystals that they use to detect sound. Biologists have for decades relied on otoliths to age fish, using them like rings on a tree. But what Reimer saw was an altogether larger, lighter, and more transparent crystal called a vaterite, growing into the otolith and obstructing the fish’s ability to hear. “I did a bit of digging and found it was much more common in farmed salmon than wild,” she says. And, she began to suspect it had something to do with the accelerated growth rates in fish farms.
Now, in a recent paper, she’s confirmed that hunch. By surveying groups of farmed salmon, Reimer discovered that the biggest feature underpinning a salmon’s likelihood of developing vaterites–beyond diet, and genetics–was their growth speed. “The fastest-growing fish were three times more likely to have vaterites than the slow-growing fish,” Reimer says. Farmed fish typically get high-nutrient feed, and are exposed to longer light conditions than they would experience in the wild. Because salmon will eat whenever it’s light, this system creates constantly guzzling fish that grow faster and more efficiently.
Reimer still doesn’t know precisely why faster growth leads to vaterite formation; one theory is that it might have something to do with rapid skeletal growth, which could usurp resources intended for the proper development of otoliths. But she does know that fish afflicted with vaterites will have impaired hearing for life. “I see this as one of many puzzle pieces in animal welfare,” she says. “What’s surprising is that we’ve known about most of the issues in aquaculture for…