Popeye is inflamation of the eyeball which caused it to swell and lock like it is poping out. The causes are variable. If the cause is due to mechanical injury, such as a fight with another fish or an abrassion from a rock, then, obviously, it is not contageous. If the cause, however, is a disease process, then the diesese causing the condition could spread. Usually, if it is caused by disease, then it is bacterial in nature, in which case you can use antibotics.