(IMAGE) Institute of Science and Technology Austria Caption Five zebrafish embryos in a tiny drop of water. The yolk sac is clearly visible, with the first two cells located at its tip. Credit © ISTA Usage Restrictions Free to use when reporting about ISTA License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.