Background

The light dark paradigm relies on rodents’ natural avoidance for open, well-illuminated areas, a behavior also called scototaxis (Champagne et al., 2010). Therefore, in the light dark task, rodents often spend more time in the dark compartment (Champagne et al., 2010; Hascoet et al., 2001). Alteration of this natural scototaxic response allows researchers to investigate the anxiogenic and anxiolytic properties of certain pharmacological agents (Sousa et al., 2006; Hascoet et al., 2001). While this paradigm has recently been adapted for use in zebrafish, the transference of this task from rodents to zebrafish has resulted in a number of inconsistencies. Unlike the nocturnal rodent, zebrafish are diurnal which may pose an issue for generalizing scototaxic and phototaxic responses across these species.

Although the light dark task has been used for a number of years in zebrafish, findings of zebrafish light dark preference remain inconsistent. Some studies have found zebrafish to prefer the black compartment (Serra et al., 1999; Maximino et al., 2010; Blaser and Peñalosa, 2011; Facciol et al., 2017), whereas others find preference for the light compartment (Gerlai et al., 2000; Champagne et al., 2010; Blaser and Peñalosa, 2011). In a study by Facciol et al. (2017), we suggested these inconsistencies may be due to a number of factors. Firstly, literature often confuses illumination level and background shade, using the term “light” interchangeably with “white”, and “dark” with “black”. Additionally, light-dark studies in zebrafish have seen a significant variation in testing tank apparatus. Factors such as the use of substrate (i.e., sand or gravel), type and levels of lighting (e.g., ambient lighting vs. tank lighting), and presence of dividers between compartments have not been kept constant across studies. These inconsistencies make it difficult to compare results across studies and may contribute to the discordant findings obtained in recent years. If these inconsistencies are indeed due to variation in testing design, standardization of testing methods is highly important for correct interpretation of pharmacological studies. The purpose of this protocol is to outline the construction and implementation of a standardized testing design for the light-dark task in zebrafish. We hope that this standardization will allow for better cross study comparison and proper interpretation of results of analyses of pharmacological agents obtained with the light-dark paradigm.