Serotonin in the Zebrafish Brain (IMAGE) California Institute of Technology Caption Two zebrafish brains, side by side, with serotonin molecules shown in red. The brain on the right comes from a fish that cannot synthesize serotonin in its raphe nuclei, leading to less of the neurochemical throughout the brain. This animal slept about half as much as a normal zebrafish (brain on the left). Credit Caltech Usage Restrictions Must use image credit 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.