Acute toxicity and sublethal effects on macromolecules concentration, caloric content, and lipid peroxidation during exogenous-feeding of Danio rerio larvae exposed to Cu²⁺

Copper is an essential micronutrient, involved as coenzyme in different metabolic processes. Due to its toxic effect, copper is also used as algicide and herbicide. Residual concentrations of this metal are released into aquatic environments as effluents from mining activities, industrial applications, and other sources, producing toxic effects on the aquatic biota. Although Danio rerio (zebrafish) embryos and larvae have been broadly used as surrogate species to assess toxic effects in water, scarce information exists on copper’s effects on fish larvae starting to feed exogenously (after yolk sac depletion). For this reason, the toxic effect of Cu on exogenous feeding larvae was assessed. Acute toxicity (96 h) was determined in 10 and 20 day post-fertilization (dpf) larvae. Additionally, the effect of sublethal Cu concentrations on the main macromolecules concentration, caloric content, and lipid peroxidation was also determined in 10 dpf larvae, as these were the most sensitive during acute exposure. The median lethal concentration (LC₅₀) and confidence limit values (P = 95%) were 148.52 ± 13.5 and 274.20 ± 40.21 μg/L for 10 and 20 dpf larvae, respectively. The caloric content, glycogen, and lipid concentration were markedly reduced in the 10 dpf larvae exposed to Cu. The malondialdehyde concentration was significantly modified in D. rerio larvae exposed during 48 h to the toxicant. Cu²⁺ concentrations as low as 16.04 and x32.08 μg/L produced biochemical impairment in D. rerio exogenous feeding larvae. Our results warn about harmful effects on the aquatic biota exposed to Cu²⁺, because its concentrations in polluted waters can be higher than those assayed here.