It is difficult to determine whether or not fish have feelings, but many scientists believe they do. Others believe that they do not have sufficient brainpower to have real feelings, and behaviors that are interpreted as signs of feeling are simply instinctive responses.
Due to the difficulty of studying emotions in fish, most research has centered around feelings of pain and stress. Fish respond to pain and to stressful environmental changes. Some of their behaviors during this time mimic self-soothing behaviors that mammals display, such as rocking back and forth. They have nociceptors, which are the same pain receptors that humans have. However, some scientists argue that the presence of nociceptors means that fish have an unconscious response to pain.