Glutathione S-transferase inducibility explains differential tolerance between Artemia franciscana and Artemia salina.

Closely related aquatic species often exhibit marked differences in their sensitivity to organic contaminants, yet the physiological mechanisms underlying this variability remain incompletely understood. This study investigated whether differences in glutathione S-transferase (GST) responsiveness are associated with contrasting phenanthrene tolerance in two congeneric crustaceans, Artemia franciscana and Artemia salina. Phenanthrene was used as a model polycyclic aromatic hydrocarbon to probe detoxification responses rather than to derive environmental toxicity thresholds. Acute toxicity was evaluated in nauplii after 24 and 48 h of exposure, whereas adult organisms were exposed for 7 days to assess survival and GST activity. Marked interspecific differences in acute sensitivity were observed. After 24 h, the EC₅₀ was 380.8 µg L⁻¹ for A. salina, whereas no EC₅₀ could be calculated for A. franciscana. After 48 h, the EC₅₀ values were 28.81 µg L⁻¹ for A. salina and 186.5 µg L⁻¹ for A. franciscana, confirming the greater tolerance of the latter species. In adults, mortality remained low in both species throughout the 7-day exposure. GST activity increased significantly in A. franciscana, showing a clear dose-dependent induction of approximately 1.7-, 1.9-, and 2.0-fold at 16, 64, and 256 µg L⁻¹, respectively. In contrast, A. salina exhibited a weaker response, with GST activity increasing significantly at 16 µg L⁻¹ but remaining relatively constant at higher concentrations. Overall, the observed differences in GST responsiveness were consistent with the contrasting phenanthrene sensitivity of the two species, suggesting that inducible phase II detoxification may contribute to interspecific differences in tolerance. These findings support the use of comparative biomarker approaches to improve the interpretation of species-specific responses to organic xenobiotics in marine invertebrates.