Depressed mood states are linked to levels of serotonin and levels of norepinephrine. low; low low; high high; low high; high

Depressed mood states are linked to low levels of serotonin and low levels of norepinephrine. Epinephrine and norepinephrine are hormones released by the adrenal medulla and the nervous system respectively. They are flight/fight hormones that are released when the body is under extreme stress. Serotonin on the other hand is an important chemical and neurotransmitter that is believed to help regulate mood and social behavior, appetite and digestion, sleep, memory, and sexual desire and function. 

That is true! many fish species traveled to the u.s. because of it.