1. An aquarium for displaying a fluorescent fish under an external lighting condition, the term “fluorescent” as used herein means the emission of light at an emission wavelength resulting from the absorption of an excitation light at an excitation wavelength lower than the emission wavelength, the aquarium comprising: an aquatic tank; a living, transgenic, fish, said fish or its progenitors having been genetically engineered such that its genome incorporates at least one exogenous fluorescent protein gene; a first light source configured to emit light at a first wavelength spectrum having a first maximum peak emission wavelength which enhances the display of said fluorescent fish within said tank under a dark external lighting condition; a second light source configured to emit light at a second wavelength spectrum having a second maximum peak emission wavelength different from said first maximum peak emission wavelength which enhances the display of said fluorescent fish within said tank under a bright external lighting condition; and at least one electronic control for controlling the operation of said first and second light sources such that the first and second light sources may be selectively turned on/off.