First baseline for bioenergetic biomarkers in Cnesterodon decemmaculatus as test organism in ecotoxicological studies.

Cnesterodon decemmaculatus is a Neotropical teleost fish frequently used in ecotoxicological evaluations, whose biology has been thoroughly studied. Although there is considerable information on its response to different toxicants, no range of reference values has been so far established for the different biological parameters proposed as biomarkers of effect or exposure. Moreover, no study has yet examined the possible influence of the metabolic status of the exposed animals on their response to toxic stress. Therefore, the aim of this work was to provide a first baseline for a set of bioenergetic biomarkers in C. decemmaculatus adults exposed to a control medium under previously standardized conditions, and to assess their possible intrinsic seasonal variability. The responses of the biomarkers obtained from the controls were contrasted with those from the reference toxicant (Cadmio-Cd) and receiving waters (surface waters of the Reconquista River RR, Buenos Aires Province, Argentina). We conducted four 12-day assays (one in each season) of exposure to control media, (reconstituted moderate hard water, MHW) and two assays of exposure to Cd in MHW and surface river water (RR) in both summer and autumn. The variables recorded were: Food intake (In), fecal production (F), specific assimilation (A) and cumulative mortality, oxygen extraction efficiency (OEE), specific metabolic rate (SMR), ammonia excretion (N), ammonia quotient (AQ) and scope for growth (SFG). The seasonal variation shown by some physiological parameters, points to the need for establishing a baseline obtained from standardized media, preferably on a seasonal basis. Moreover, SFG and A appeared as the most sensitive biomarkers, emphasizing the importance to consider the metabolic status of the test organisms for the appropriate interpretation of results from ecotoxicological studies performed under controlled experimental conditions. The obtained results provide useful information on C. decemmaculatus as model species in ecotoxicological bioassays involving biomarkers of early effect.

Evaluation of the Acute Effects of Arsenic on Adults of the Neotropical Native Fish Cnesterodon decemmaculatus Using a Set of 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. Environ Toxicol Chem 2022;41:1246-1259. © 2022 SETAC.