The U.S. Food and Drug Administration is weighing whether to allow a genetically engineered Atlantic salmon to be the first such animal to be sold as food. The fish is made by Aqua Bounty Technologies Inc

The following are four other genetically engineered animals in development or approved by the FDA.

ENVIROPIG

University of Guelph scientists are awaiting word from the FDA on their Enviropig, a type of Yorkshire pig with genes altered to affect digestion. They hope it will be the second FDA-approved genetically engineered food animal.

The pig is engineered with a mouse protein that affects its saliva. The aim is to create more environmentally friendly manure by reducing the amount of phosphorous the pig excretes after eating cereal grain. Phosphorous can leach into waterways and increase the amount of fish-killing algae.

MAD COW RESISTANT CATTLE

Hematech Inc in Sioux Falls, South Dakota, is developing cows that are resistant to mad cow disease (bovine spongiform encephalopathy).

Called TC Bovine, the cows could help researchers develop treatments for some human illnesses, according to Hematech, which has said the cow could be a food source.

Researchers said they developed the cow by knocking out the prion protein gene that can trigger mad cow disease.

Hematech is a subsidiary of Kirin Holdings Co Ltd's Kyowa Hakko Kirin Company.

GOATS

In February 2009, the FDA approved GTC Biotherapeutics Inc's modified goats used to produce an anti-clotting therapy for people with a rare disorder called hereditary antithrombin deficiency. The drug, Atryn, is made with human protein from female goats bred to express it in their milk.

The company, in Framingham, Massachusetts, has said its roughly 200 goats are bred using cells injected with human DNA. The drug is licensed in the United States to Lundbeck Inc.

GLOFISH

In December 2003, the FDA said there was no reason for it to regulate the GloFish, a zebra danio fish genetically altered with fluorescent colors, because it was not intended for food and posed no environmental threat.

The fish was originally developed to help detect polluted waterways using a fluorescent protein gene that occurs naturally in other marine organisms, according to Yorktown Technologies, LP.

The company sells the fish nationwide except in California, which required a formal environmental study that Yorktown said was too expensive.