Effect of nicotine (1 mg/L) pre-exposure for 2 weeks in the Novel diving tank test. Behaviour was evaluated for 5 min on Day 2, 7, 30 and 60 after nicotine cessation, during spontaneous withdrawal, in terms of (a) time spent in the top,(b) latency to top and (c) the number of transitions to top. Data are mean ± SEM. Comparisons were performed using two-way ANOVA followed by post-hoc Bonferroni test. N = 10 animals for each group. *p < 0.05,**p < 0.01,***p < 0.001 compared to the corresponding drug-free zebrafish; $ $ $p < 0.001, &&&&p < 0.0001 compared to the corresponding nicotine group, Day 2.