Research has shown that indeed they can. According to Dr. Donald Broom, animal welfare advisor to the British government, “Anatomically, physiologically, and biologically, the pain system in fish is virtually the same as in birds and mammals.” Fish have fully developed brains and nervous systems and very sensitive mouths. Fish use their tongues and mouths as humans might use their hands—to catch or gather food, build nests, and even hide their offspring from danger. Fish also experience fear. An Australian study found that when fish are chased, confined, or otherwise threatened, they react as humans do to stress: with increased heart and breathing rates and a burst of adrenalin.