Fig 2. Nitrate and nitrite treatment were associated with an initial decline in learning, but fish learned over repeated tests.

Adult zebrafish were treated with control water, sodium nitrate, or sodium nitrite for 14–17 days when learning and memory were tested in the shuttle box assay (n = 72–109). (A) Time-to-decision and time shocked was recorded for each fish and trial (dots) and linear regression of the data were calculated (lines). As calculated from the linear regression the bars indicate (B) initial periods of time fish spent for the indicated measure and (D) rates of learning as quantified by the slope from the linear regression. (C) Bars indicate the percentage of fish that were removed from the assay because they did not swim to the correct side during eight consecutive trials. (E) Statistical summary of shuttle box results as calculated by an analysis of variance (AOV) followed by a Tukey’s post-test where “All” indicates data from all fish analyzed, while “Completed trials” excludes data from fish that repeatedly failed.