Influence of interspecific interactions on avoidance response to contamination.

An increasing number of studies have shown the ability of organisms to escape from toxic effects due to contamination, by moving spatially towards less contaminated habitats. However, this issue has been investigated in monospecific scenarios, without considering possible interactions between species during the contamination avoidance process. It is widely known that the spatial distribution of one species can be affected by another one, in different ways. Therefore, the main question addressed in the present study was as follows: Might interspecific interaction between the freshwater fish Danio rerio (zebrafish) and Poecilia reticulata (guppy) change their behavior patterns in terms of avoidance in the presence of a copper gradient? Zebrafish and guppies exposed to a copper gradient were tested for avoidance responses in a free-choice, non-forced, static, multi-compartmented exposure system, using two distinct approaches: (1) monospecific tests, in which only one species was exposed to the copper gradient, at two different population densities; and (2) multispecific tests, in which both species were tested simultaneously. In the control (with no copper) monospecific tests, both species were randomly distributed; however, in the control multispecific test, P. reticulata tended to aggregate. In the monospecific tests with a copper gradient, both species avoided copper in a similar way, with AC50 (concentration triggering avoidance in 50% of the exposed population) values between 15 and 18 µg·L-1, irrespective of the population density. However, in the multispecific tests, P. reticulata displaced D. rerio to previously avoided copper levels, consequently increasing the AC50 of D. rerio to 75 µg·L-1. This study shows the importance of understanding the interactions among species in contaminated areas, and the way that one species can prevent the avoidance behavior of another.

Bisphenol risk in fish exposed to a contamination gradient: Triggering of spatial avoidance.

Bisphenol A (BPA) is an emerging contaminant widely used in various industrial products. Sublethal toxicity of BPA on aquatic organisms is expected to occur at a concentration of around 500 µg L-1, which is much higher than environmentally realistic concentrations found in water bodies (up to 0.41 µg L-1). However, there is no information concerning how a BPA contamination gradient could affect the spatial displacement of organisms. We hypothesized that fish might be able to detect an environmentally realistic BPA contamination gradient and avoid potential toxic effects due to continuous exposure. Therefore, the objectives of this work were: (i) to determine if BPA could trigger an avoidance response in the freshwater fish Poecilia reticulata; (ii) to assess whether BPA-driven avoidance occurs at environmentally relevant concentrations; and (iii) to estimate the population immediate decline (PID) at the local scale, considering avoidance and mortality as endpoints. Avoidance experiments were performed in a seven-compartment non-forced exposure system, in which a BPA contamination gradient was simulated. The results indicated that BPA triggered avoidance in P. reticulata. In a traditional forced acute toxicity test, lethal effects in 50% of the population occurred at a BPA concentration of 1660 µg L-1, while in the non-forced system with a BPA concentration gradient, avoidance of 50% of the population occurred at a concentration four orders of magnitude lower (0.20 µg L-1). At environmentally relevant BPA concentrations, PID was mainly determined by the avoidance response. Avoidance in P. reticulata populations is expected to occur at BPA concentrations below those that cause sublethal effects on fish and are considered safe by international agencies (≤1 µg L-1). The approach used in the present study represents a valuable tool for use in environmental risk assessment strategies, providing a novel and ecologically relevant response that is complementary to traditional ecotoxicological tests.

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

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.