Effects of nicotine and alcohol on zebrafish (Danio rerio) shoaling

The zebrafish has been used in the analysis of the effects of drugs of abuse, including alcohol and nicotine. In the current study, we investigate the effects of these drugs on shoaling, group-forming behavior, in zebrafish, using a newly developed set of behavioral measures. We expose our fish acutely to 0.25, 0.50, 0.75 or 1.00% (% v/v) ethyl alcohol or 4 or 8 mg/L nicotine by immersing the fish in the corresponding solutions. The behavior of the exposed fish is compared to controls in a large (91 cm diameter) circular tank in which shoals of 8 subjects under the same treatment are allowed to swim freely. Several measures of shoaling are quantified including the nearest neighbour distance (NND), inter-individual distance (IID), swimming speed, polarization (a measure of the directional synchronization of the shoal), and the number and duration of excursions (departures from the shoal). Alcohol and nicotine were both found to exert significant effects on shoaling but impaired the behavior in different ways. For example, alcohol strongly disrupted polarization and only modestly reduced shoal cohesion, while nicotine had only a modest effect on polarization but robustly decreased shoal cohesion. Neither drug affected the number or the duration of excursions, but both reduced swimming speed. These results underscore the notion that using multiple measures of social behavior may allow one to characterize and distinguish different aspects of drug effects on behavior, which may facilitate discovery of novel drugs in drug screens and may also be utilized in the analysis of underlying mechanisms.