GloFish are fluorescent fish that were originally bred to help detect environmental pollutants. Read the GloFish FAQ: About GloFish. Of course, who wouldn't want a flourescent fish for the dull, unexciting fish tank at home? So, they are now available for sale to the general public (Buy GloFish Fluorescent Fish). But be aware. These fish are licensed (GLOFISH FLUORESCENT FISH LICENSE NOTICE):

The GloFish fluorescent ornamental fish are intended solely for visual enjoyment as aquarium fish by end users who have purchased these fish from authorized resellers, and not for commercial reproduction. These fish are the subject of various intellectual property rights owned or controlled by Yorktown Technologies, Inc. (“Yorktown”), both in the U.S. and internationally. These rights include (1) patent rights, including published patent applications (2) copyrights; and (3) trademark rights, including slogans and service marks.

By accepting these fish, and as part of the consideration therefor, the recipient agrees: (1) not to, breed or propagate these fish, permit or encourage others to breed or propagate these fish, or otherwise intentionally engage in any activity that may result in or lead to the breeding or propagation of these fish by anyone without the express written consent of Yorktown; (2) not to sell or transfer these fish to anyone in the State of California, or to possess or otherwise engage in any activity that results in the possession of these fish in the State of California.

via Ed Foster's Gripe Log

UPDATE 1255PT A commentor notes that the fish were banned in California. CNN with an AP wirestory (California Blocks Sales of 'Glofish' Pets).