Microscope shows first hours of developing embryo

"This is like being able to watch an animal getting a life," said Joachim Wittbrodt, who led the study published in the journal Science while at the European Molecular Biology Laboratory in Heidelberg, Germany.

"You have a clump of cells that are transforming into an embryo with a beating heart while you are watching."

"The power is in the size and the resolution while at the same time being extremely gentle on the embryo and extremely fast, which you need to follow things that are moving," said Wittbrodt, now at the University of Heidelberg in Germany.

"It's like a huge puzzle and we can see the individual pieces. We see everything."

Zebrafish, also known as zebra danio, are popular research subjects because they are cheaper to breed than mice and share a number of similar biological traits with humans.

To develop into a complex organism, an embryo's cells must divide, travel around the body and arrange themselves into intricate shapes and specialized tissues. So far the researchers said they have identified how some of this cell migration is different to what was previously believed.

Eventually, such experiments could provide a better understanding of how tumors spread or why cells sometimes turn against the body in autoimmune diseases like arthritis, Wittbrodt said.