guppy (n.) Look up guppy at Dictionary.com
1918, so called about the time they became popular as aquarium fish, from the scientific name (Girardinus guppii), which honored R.J.L. Guppy, the British-born Trinidad clergyman who supplied the first specimen (1866) to the British Museum. The family name is from a place in Dorset. Other early popular names for it were rainbow fish and million fish. The class of streamlined U.S. submarines (1948) is an acronym from greater underwater propulsion power + -y.