This is like one of those weird discussions about light being accelerated beyond light speed so it in fact exits an experiment before it enters. My head hurts. I'm having a lie down.
They do not have higher brain functions neccessary to be conciously aware of their enviroment and therefore are incapable of feeling any emotions, bad or good. However, as I said, certain species of fish which breed for life may refuse to eat, or even die from the loss of a mate. Certain stimuli, or lack of stimuli can cause extreme stress on them, leading to all sorts of issues.