The impact of xenobiotics in organisms at the biochemical level can be detected using specific or nonspecific biochemical markers. Activity of the enzyme arginase is used as a biochemical parameter of cell proliferation in mammals because of its importance in polyamine synthesis, which provides molecules for cellular growth and differentiation. Therefore, total arginase activity could indicate sublethal organism alterations induced by xenobiotics. In the present study, bioassays with early stages of Danio rerio were implemented using the pesticide malathion as a reference toxicant and a kraft pulp mill (KPM) effluent to assess their potential toxicity. The experimental design considered a 144-h static bioassay that involved incubation from an early 3-h postfertilization embryonic stage through to the eleutheroembryo stage. Growth variations and observations of organ development were evaluated and related to total arginase activity. The enzymatic activity in eleutheroembryo exposed to malathion exhibited a significant decrease at concentrations equal to or higher than 3 mg/L. Delays in the early development and morphometric parameters suggest metabolic depression in these conditions. A significant positive relationship between total arginase activity and eleutheroembryo development was observed, indicating that a decrease in total arginase activity might be related to sublethal alterations in eleutheroembryo growth. Bioassay results with KPM effluents resulted in a delay in organogenesis only in effluent concentrations of 100% and were related to a significant decrease in total arginase activity. In conclusion, total arginase activity has a higher sensitivity compared with morphological parameters in providing an early signal of the sublethal effects on early life stages of fish exposed to environmental stress.
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