Glofish is the name given to genetically modified zebra danios (Brachydanio rerio). Their name is correctly spelled as glofish, but is sometimes incorrectly spelled as glowfish. This is a common mistake because the fish do seem to glow when they encounter environmental toxins.
The difference between regular zebra danios and glofish are that researchers in Singapore added a fluorescence gene from a sea coral to zebra danio eggs to produce glofish. This gene causes the genetically modified fish to fluoresce or light up in the presence of environmental toxins.
Other than this, they are identical to regular zebra danios, with the exception that the genetically modified glofish have neon colors. Regular zebra danios are gold and blue striped or gold and silver striped fish. Both glofish and regular zebra danios are peaceful fish that do well in a community tank.
Originally created to detect environmental toxins, glofish have been for sale in pet stores since 2003 for the general public to buy and place in their aquariums. There is some concern about what might happen if these genetically altered fish find their way into natural rivers and streams. The creators of glofish state that they don't pose an ecological threat because glowfish, like regular zebra danios, won't survive in the wild because they are tropical fish and need a water temperature of about 24-26 °C (75-79 °F). It's been five years now and so far there doesn't seem to be a problem. Although some people do question the ethics of selling genetically altered fish to the public just because they are prettier than the original fish.
Glofish come in a variety of colors, including red, green, and orange. They can be purchased for about $6-7 each.
Glofish are reported to be as healthy as regular zebra danios and their care is identical. They reach an adult size of approximately 2 inches (5 cm). They are omnivores that eat a variety of aquarium fare.
Zebra danios are some of the easiest egglaying fish to breed in the aquarium, and glofish should be no different. If you have a pair of glowfish that spawns in the aquarium, their fry will also be glofish and not plain zebra danios. For regular zebra danios it is possible to tell the difference between males and females. Females have blue and silver stripes and males have blue and gold stripes, and the females usually have more of a rounded bodyshape. Other than body shape I'm not certain how you determine the sex of glofish.
During spawning they scatter their eggs. As with regular zebra danios, you should place marbles in the bottom of the breeding tank so that the parents won't be able to eat the eggs. You should also have plants in your spawning tank. After spawning is complete remove the parents from the tank and place them back into the regular aquarium.
The eggs should hatch in 1-3 days. Once the fry are free-swimming they can be fed liquid commercial fry food or infusoria. They are too small at first to eat brine shrimp nauplii, but in a week or two this should be added to their diet as well as powdered fry food.