Capricorn is associated with the tenth house of the zodiac and with the planet Saturn. I don't know what any of that means, but if you are into astrology it no doubt is important. People that are born under the sign of Capricorn (Dec. 22 to Jan. 20) are patient, practical, disciplined and reserved. Capricorn is symbolized by a goat - usually a sea goat. I don't think there is a real animal called a "sea goat" (fish tail, goat head). There is an unsupported "theory" as to why on wikipedia -
"However, the constellation is more often depicted as a goat with a fish's tail. One myth says that when the goat-god Pan was attacked by the monster Typhon, he dove into the Nile; the parts above the water remained a goat, but those under the water transformed into a fish."Sometimes the Capriconus constellation is called Amalthea, the goat that suckled the infant Zeus after his mother Rhea saved him from being devoured by his father Cronos (in Greek mythology). The goat's broken horn was transformed into the cornucopia or horn of plenty. Yet another piece of party trivia for you - what animal does a cornucopia come from?