Fig. 1. Schematic diagram of the experimental design.

Fig. 2. Swimming activity of control (top), Hg- (middle) and As-exposed (bottom) zebrafish at ML (left panels) and MD (right panels) (n = 14 fish/trial). Activity levels were normalized as the percentage of maximum velocity displayed by fish during each trial. As and Hg exposure period are indicated by a grey rectangle.

Fig. 3. Mean locomotor activity level (cm/s) of control (top), Hg- (middle) and As-exposed (bottom) zebrafish at ML (left panels) and MD (right panels) (n = 14 fish/trial). Each bar indicates the average activity level during 30 min ±SE. White and black bars represent activity data from non-exposed fish (control) and before adding the metals to the aquarium at ML and MD, respectively. Pattern filled bars represent data from Hg- (dots) and As-exposed (grid) fish. Asterisks (*) indicate statistically significant differences in mean activity levels between the first and the subsequent 30-min slots (GLM Repeated measures followed by pairwise comparisons, Bonferroni adjusted, p < 0.05).

Fig. 4. Relative expression of antioxidant genes in gills (left panels) and liver (right panels) of control and Hg-exposed zebrafish at ML (white bars) and MD (black bars): sod1, gpx7, gsr and cata. Data are shown as the mean ± SE (n = 7). Capital superscript letters indicate statistically significant differences between treatment means (ANOVA II, p ≤ 0,05). Lower case superscript letters indicate statistically significant differences between all experimental groups when a significant interaction “treatment x time” was found (ANOVA II, p ≤ 0.05 followed by multiple pairwise comparisons, Bonferroni-adjusted, p < 0.05).

Fig. 5. Relative expression of antioxidant genes in gills (left panels) and liver (right panels) of control and As-exposed zebrafish at ML (white bars) and MD (black bars): sod1, gpx7, gsr and cata. Data are shown as the mean ± SE (n = 7). Capital superscript letters indicate statistically significant differences between treatment means (ANOVA II, p ≤ 0,05). Asterisks indicate statistically significant differences between time point means (ANOVA II, p ≤ 0.05). Lower case superscript letters indicate statistically significant differences between all experimental groups when a significant interaction “treatment x time” was found (ANOVA II, p ≤ 0.05 followed by multiple pairwise comparisons, Bonferroni-adjusted, p < 0.05).

Fig. 6. Relative expression of mt2 gene in gills (left panels) and liver (right panels) of control, Hg- (A) and As-exposed (B) zebrafish at ML (white bars) and MD (black bars). Data are shown as the mean ± SE (n = 7). Graph definitions are as provided in Fig. 4.

Fig. 7. Hg concentration (mg/Kg) in liver (A), gills (B), and brain (C) of zebrafish exposed to Hg at ML (white bars) and MD (black bars) for 6 h. Graph definitions are as provided in Fig. 4.