Studies Find Depression and Hearing Loss in Farmed Salmon

Posted on May 25, 2016

Healthy salmon and loser drop-out salmon

Recent studies have found that farm raised salmon can suffer from depression. They can also suffer from hearing loss. Some salmon even become known as "drop out" or "loser fish."

Discovery News reports on the study that found many farm raised salmon exhibit similar behaviors and brain chemistry to depressed humans. Discovery says the so-called drop-out fish float at the surface of tanks "seemingly wanting to die." The photograph above shows a healthy Atlantic salmon on top and a depressed loser drop-out salmon underneath.

The lead author of the study didn't want to call it suicide but says the fish have been pushed to their limits. Marco Vindas, of the University of Gothenburg, told Discovery News, "I would not go so far as to say they are committing suicide, but physiologically speaking, they are on the edge of what they can tolerate, and since they remain in this environment, they end up dying because of their condition."

The depressed fish study was published here in the journal, Royal Society Open Science. A separate study published in Scientific Reports found that half of the world's most farmed marine fish, Atlantic salmon, have a deformity of the otolith or "fish earbone." This deformity is associated with hearing loss. It is very uncommon in wild Atlantic salmon.

Lead author Ms Tormey Reimer from the University of Melbourne says in a statement, "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% of their hearing sensitivity."

Study co-author Professor Steve Swearer from the University of Melbourne adds, "All native fish re-stocking programs should now assess if their fish have deformed earbones and what effect this has on their survival rates. If we don't change the way fish are produced for release, we may just be throwing money and resources into the sea."

Photo: Ole Folkedal