Ear bone: the left one (of a wild salmon) is normal and the one on the right (of a salmon in captivity) is deformed.
Sao Paulo-a new scientific research, published in the scientific journal Scientific Reports, revealed for the first time that half of fish bred in captivity in the world presentloss of hearing due to a deformity in the ear.
As with other vertebrates, fish have a hearing aid that is essential not only to the hearing as well as to the balance. Your ears are built-in, embedded in the bones of the skull.
The researchers at the University of Melbourne, who led the study, found that half of the world's marine fish bred in captivity, such as Atlantic salmon, have a deformityin Otoliths, the calcareous bodies located in the inner ear, anything unusual presentin wild fish.
According to the lead author of the study, Tormey Reimer, farmed fish are 10 timesmore likely to have the deformity than those that develop freely in the sea.
"The deformity occurs when the typical structure of calcium carbonate in the fish's ear is replaced by a different crystal form. These ' deformed ' bones are larger, lighter and more fragile, "said Reimer.
According to the researcher, the deformity appears at an early age, most of the time when the fish are in an incubator, but its effects on hearing become increasingly serious as they grow.
Research suggests that fish suffering with this deformity can lose up to 50% of his hearing sensitivity.
To test if the problem was a global phenomenon, the researchers at the University of Melbourne joined the Norwegian Institute for Nature research and collected samples of salmon in major producing Nations in the world: Norway, Canada, Scotland, Chile and Australia.
The team compared the structure of the Otoliths of Sockeye Salmon raised in nursery and of the wild and also the hearing of fish. They found that, irrespective of the country where salmon is farmed, the deformity is much higher in farmed fish than in wild animals.
It's clear that something about the process of cultivation is causing this deformity, but the researchers now need to figure out what leads to it.
Violations
According to the researchers, the production of captive animals with deformities violates welfare definitions set out in the Universal Declaration of Animal welfare and which form the basis of legislation to ensure a proper management of farm animals in many countries.
According to the researchers, the deformity could also explain why many fish conservation programs are not working as expected.
Every year, thousands of young salmon raised in captivity are released into rivers in North America, Asia and Europe, to boost wild populations, but their survival is 10 to 20 times lower than wild salmon.
Hearing loss, in this case, can prevent the fish to detect the presence of predators in addition to restrict your ability to follow the migratory flow of species for breeding.
"We think the hearing impaired could be part of the problem. All native fish restocking programs now must assess whether the fish has ear deformities and what effect it has on their rates of survival, "said study co-author Steve Swearer, the University of Melbourne.
