Potential effects of triclosan on spatial displacement and local population decline of the fish Poecilia reticulata using a non-forced system

- Spatial avoidance by the fish Poecilia reticulata exposed to triclosan was studied.
- A non-forced exposure system was used to simulate a triclosan gradient.
- Triclosan has the capacity to trigger an avoidance response in P. reticulata.
- Avoidance was concentration-dependent, but was not dependent on the gradient pattern.
- Triclosan can cause a fish population decline at local scale even at sublethal levels.

Triclosan (TCS) is an emerging contaminant of concern in environmental studies due to its potential adverse effects on fish behavior. Since avoidance has been shown to be a relevant behavioral endpoint, our aims were: (i) to determine if TCS is able to trigger an avoidance response in Poecilia reticulata; (ii) to predict the population immediate decline (PID) caused by TCS exposure, by integrating lethality and avoidance responses; and (iii) to verify the overestimation of risk when mortality is assessed under forced exposure. Fish were exposed to TCS in a forced exposure system, to assess mortality, and to a TCS gradient in a non-forced exposure (NFE) system. Two NFE scenarios were simulated: (#1) a spatially permanent gradient, including low and high concentrations; and (#2) a scenario with high concentrations, simulating a local discharge. The fish avoided TCS concentrations as low as 0.2 μg L−1 (avoidance of 22%). The AC50 obtained from scenario #1 (8.04 μg L−1) was about 15 times more sensitive than that from scenario #2 (118.4 μg L−1). In general, up to the highest concentration tested (2000 μg L−1), the PID was determined by the avoidance. Mortality from the forced exposure was overestimated (48 h-LC50 of 1650 mg L−1), relative to the NFE. The reduced mortality in a non-forced environment does not imply a lower effect, because part of the population is expected to disappear by moving towards favorable environments. TCS is a potential environmental disturber, since at environmentally relevant concentrations (<2 μg L−1) it could cause a decline in the fish population.