Trinidadian Guppies (VIDEO) University of Exeter This video is under embargo. Please login to access this video. Caption Guppies rapidly turn their irises from silver to black before attacking smaller rivals. Credit Robert Heathcote, University of Exeter Usage Restrictions This video may only be used with reports of this research License Licensed 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.