From colours to cravings: Exploring conditioned colour preference to ethanol in zebrafish

Conditioned preference paradigms like conditioned colour preference tests (CCP) can be used to investigate addictive drug seeking in zebrafish (Danio rerio), but many aspects of this procedure require further study. Conditioned preference can be tested with either biased or unbiased conditioning methods, each with their own strengths and weaknesses. The present study used unbiased stimuli to test seeking behaviour in ethanol-exposed zebrafish at different durations of drug withdrawal. Zebrafish were exposed to one of two equally preferred colours (red or yellow) while dosed with 0.8 % vol/vol ethanol or with habitat water (controls) for 1 h each day for 21 days. Next, fish experienced withdrawal for either 2-, 4-, or 8-days then were tested in a two-way red and yellow task for 10 min with their movement recorded via motion-tracking software. Fish conditioned to red showed a main effect of ethanol and a significant preference for red compared to yellow at 8-days of withdrawal but not at 2-days or 4-days of withdrawal. Fish conditioned to yellow did not show any colour preference during the 2-, 4-, or 8-days of withdrawal, but did show a main effect of withdrawal duration. This work expands our understanding of CCP paradigms in zebrafish and highlights the capacity of zebrafish to develop an association to red but not yellow under our experimental conditions.