Zebrafish, Danio rerio, are freshwater fish that were originally found in slow streams and rice paddies and in the Ganges River in East India and Burma. In the early 1970's, a scientist at the University of Oregon, Dr. George Streisinger, determined that the zebrafish is a remarkable model for studying vertebrate development and genetics. Males are slender and torpedo-shaped, usually with gold on their belly, ventral fin, pelvic fins, and pectoral fins. Males can also be identified by their tendency to chase the females early in the morning before they breed. Females are fat when filled with eggs and do not usually have gold on their undersides.