After norepinephrine (IMAGE) Howard Hughes Medical Institute Caption When a zebrafish experiences stress, specialized cells called iridophores that house microscopic, light-reflecting guanine crystals can shift from blue to a vibrant yellow (shown here) by adjusting the angle of the crystals inside of them, a remarkable transformation driven by motor proteins. Credit Dvir Gur Usage Restrictions Please use caption and credit. 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.