Piscis Austrinus, latin for "Southern fish", is a constellation on the southern hemisphere, south of Aquarius and Capricornus. It is an elongated smallish constellation, and represents a single fish. The alpha star (the constellation's brightest star) is Fomalhaut, which is arabic for "fish's mouth". The constellation is quite prominent because Fomalhaut is the only relatively bright star in that area.
Many of the old star charts depics Piscis Austrinus as drinking from the water that flows out of Aquarius' jar.