Box plots of behavioral variation among two wild and two domesticated zebrafish strains. (a) Domesticated zebrafish [Scientific Hatcheries (SH) and TM1] had lower Vertical Depth, spending more time close to the water surface than wild zebrafish [Nadia and Gaighatta] (P < 0.0001). (b) Domesticated zebrafish also had higher levels of Horizontal Position, spending a larger portion of time within one body length of the front of the aquarium nearest the human observer (P < 0.0001). Boxes represent the 25th and 75th percentiles, while the median is indicated by the interior horizontal line. The 5th and 95th percentiles are represented by the whiskers. Significant differences among strains are represented by lower case letters within each figure.