Researchers find that growth-stunted farmed salmon show chronic serotonergic activity and do not respond to acute stress — a state that could be interpreted as depression.
In the vertebrate brain, serotonin mediated signaling is vital for several key physiological functions such as the body’s energy regulation, neural plasticity, behavioral and emotional control, and responses to stress. However, prolonged serotonin activation is associated with chronic stress and stress-induced pathologies in mammals. Such states include depression-like behaviors. This paper represents the first physiological data, showing that growth-stunted commercially farmed salmon have elevated serotonergic activity; what’s more, this is determined as the main characteristic of the growth-stunted phenotype. Compared to healthy fishes, these salmon are suggested to experience chronic stress. In fact, the researchers show that the fishes’ brains are not responsive to additional acute stress, representing a classic example of when regulatory mechanisms are unable to react to further challenges, indicating a depressive state.