No abstract

Recognising biomarkers for assessing early ecotoxicity effects using test species exposed to reference toxicants is important, hence the aim of this work was to study changes in some behavioural parameters of Cnesterodon decemmaculatus. Fish were under stress conditions induced by exposure to a subtoxic concentration of cadmium (Cd) in the laboratory. Acute bioassays (96 h) were performed under laboratory conditions, with medium renewal every 48 h. Animals were randomly assigned into two groups of 10 individuals each: Cd-exposed (0.50 mg Cd. L -1 ) and control (moderate tap water). Both groups were video-recorded every day for 15 min at the same time of day. Each individual was evaluated for: a) aggressive behaviour; b) sexual behaviour; and c) swimming alterations. Fish exposed showed irregular swimming, hyperactivity periods, fewer copulation attempts and same aggressive behaviour as compared with the control group. Our results suggest that these behavioural alterations may serve as early and reliable biomarkers.

Neotropical fish Cnesterodon decemmaculatus were exposed to different sublethal concentrations (0.5, 1.0 and 5.0 mg As/L) of sodium arsenite (As III) to determine the median lethal concentration (LC50; 96 h) and to evaluate the response of a set of biomarkers (genotoxic, behavioral, biochemical, and metabolic). At the end of the exposure (96 h), fish were video-recorded for behavior assessment. We used the micronucleus and nuclear abnormality tests and the comet assay in peripheral blood as genotoxicity biomarkers. In regard to biochemical and metabolic biomarkers, we dissected the brain for acetylcholinesterase (AChE) activity; the liver for glutathione-S-transferase (GST) and catalase (CAT) activity and glutathione content (GSH); the gills for GSH content; and muscle for AChE, energy metabolism of lipids, carbohydrates, and proteins, and the electron transport system activity of the mitochondrial chain. We calculated an index using metabolic biomarkers, to determine the cellular energy allocation. The LC50 value was 7.32 mg As/L. The As affected some swimming parameters in females. No significant differences in micronucleus were found compared with the control, whereas nuclear aberrations increased significantly at 1.0 and 5.0 mg As/L. The genomic damage index and the percentage of cells with DNA damage (measured by the comet assay) showed a significant increase in the As-treated groups, and this technique was the most sensitive for detecting genotoxic damage. The As affected the antioxidant system (mainly GSH, CAT, and GST) and reduced the lipid content. A preliminary baseline was generated for the response of C. decemmaculatus exposed to sublethal concentrations of As, when it alters swimming behavior and the antioxidant system, has genotoxic effects, and reduces lipid content.

Cnesterodon decemmaculatus, which is a freshwater fish abundant in the Pampean region of Argentina, is used as a bioindicator of the status of watercourses throughout its distribution area. This work aimed to (1) evaluate the genetic diversity and population structure of C. decemmaculatus from two river basins in north-eastern Buenos Aires province, Argentina, (2) assess a possible association between genetic structure and the geographical distribution of river basins, including in the analysis data of populations from the south of the province, and (3) validate the use of the species as a bioindicator of the ecological status of watercourses in north-eastern Buenos Aires province. The analysis of a 700-bp fragment of the mitochondrial DNA control region showed moderate to high levels of genetic diversity and lack of genetic structure between the north-eastern basins, validating the use of this species as a bioindicator. Significant differences in genetic structure were found among basins at a regional scale. The lack of genetic structure between the north-eastern basins may result from historical and current events, whereas genetic differences between the north-eastern and southern basins may be explained by the absence of physical connections between them.