Avoidance response of Danio rerio to a fungicide in a linear contamination gradient

The present study examines the ability of juvenile Danio rerio to avoid pyrimethanil-contaminated water. An avoidance assay system was used with a contamination gradient formed by seven compartments, through which the fish could move and choose the preferred compartment(s). Additionally, the influence of fish movements in promoting the mixing between compartments and thus disruption of the gradient over time was also examined by testing sodium chloride (NaCl) at sublethal concentrations. Samples with pyrimethanil were obtained from the commercial formulation Mythos®, which was applied to mesocosm systems. Samples of the pyrimethanil-contaminated mesocosms water were collected and a series of seven concentrations (0.2 to 1.4mgL(-1) plus a control) diluted with reference (uncontaminated) mesocosm water were added to the system to form the gradient. After 4h exposure, fish avoidance in the three highest pyrimethanil concentrations ranged from 29 to 66%. The 4h-AC50 (concentration at which 50% of the fish avoided pyrimethanil after 4h exposure) was 1.10 (confidence interval: 1.07 to 1.12)mgL(-1). However, the avoidance pattern after 12h was strongly reduced and it was not possible to calculate the AC50. This is explained by the results of the NaCl experiment, which showed that the movement of fish in the system accelerates the mixing of the solutions between compartments. As pyrimethanil can trigger avoidance response in D. rerio, this fungicide, even at non-lethal concentrations, could be considered an environmental disturber.