Spatial avoidance, inhibition of recolonization and population isolation in zebrafish (Danio rerio) caused by copper exposure under a non-forced approach

Abstract

Aquatic ecosystems receive run-off and discharges from different sources that lead to the accumulation of contaminants such as copper. Besides producing lethal and sub-lethal effects, copper has shown to be aversive to zebrafish (Danio rerio) by triggering avoidance response. The primary aim of the present study was to evaluate how a copper gradient could affect the spatial distribution of D. rerio by triggering avoidance, preventing recolonization and isolating populations. Secondly, to what extent the food availability in a previously avoided environment could make it a less aversive environment was assessed. A non-forced, multi-compartmented exposure system with a copper gradient (0-300 μg·L^-1), through which fish could move, was used for the avoidance and recolonization assays. To test the effect of copper on population isolation, two uncontaminated connected zones were separated by a chemical barrier with a copper concentration of 90 μg·L^-1 (a concentration producing an avoidance of 50% - AC₅₀). Zebrafish avoided copper and the 2 h-AC₅₀ was 90.8 μg·L^-1. The recolonization was in accordance with avoidance and the relationship AC_x/RC_100-x (RC: recolonization concentration) was around 2.5. When food was provided in the highest copper concentration, the recolonization pattern was altered, although the distribution of the fish was not statistically different from the scenario without food. The chemical barrier formed by copper (90 μg·L^-1) impaired the migratory potential of the fish population by 41.3%; when food was provided in the last compartment, no statistically significant trend of fish moving towards that concentration was observed. Copper might act as an environmental disruptor by triggering spatial avoidance, preventing recolonization and isolating populations in zebrafish. The present study allows simultaneously including three ecological concepts to ecotoxicological studies that have received little attention: habitat selection, recolonization and habitat chemical fragmentation.

Keywords: Avoidance; Copper; Food attractiveness; Habitat fragmentation; Non-forced exposure; Recolonization.