A Standardized Tank Design for the Light Dark Task in Zebrafish.

The light dark paradigm is a common behavioral test used to screen a variety of pharmacological agents, including anxiogenics and anxiolytics. Although most often used in rodents, the light dark task has recently been adapted for use in zebrafish. However, a number of inconsistent findings have been reported for this species. Some have found zebrafish to prefer black, while others report a preference for light. Careful analysis of light dark preference experiments using zebrafish reveals significant variation in testing tank design and test conditions, including lighting and substrate color. Additionally, in some experiments the designated dark side of the testing tank is completely covered, producing a "cave-like" environment which further confounds results. Lastly, authors commonly use the terms "light vs. dark" interchangeably with "white vs. black", when these are two separate factors that may influence preference: illumination level vs. background shade. To address these limitations, we designed testing tanks that differentiate illumination vs. background shade preference in zebrafish. This design allows for simple standardization of light dark testing apparatus in zebrafish, and facilitates more reliable comparison across studies.