Acute sublethal exposure to ethiprole impairs physiological and oxidative status in the Neotropical fish Astyanax altiparanae.

Ethiprole, a phenylpyrazole insecticide, has been increasingly used in the Neotropical region to control stink bug pests in soybean and maize fields. However, such abrupt increases in use may have unintended effects on non-target organisms, including those inhabiting freshwater ecosystems. Here, we evaluated the effects of acute (96 h) sublethal exposure to ethiprole (up to 180 µg/L, which is equivalent to 0.013% of the recommended field dose) on biomarkers of stress in the gills, liver, and muscle of the Neotropical fish Astyanax altiparanae. We further recorded potential ethiprole-induced effects on the structural histology of A. altiparanae gills and liver. Our results showed that ethiprole exposure increased glucose and cortisol levels in a concentration-dependent manner. Ethiprole-exposed fish also exhibited higher levels of malondialdehyde and greater activity of antioxidant enzymes, such as glutathione-S-transferase and catalase, in both gills and liver. Furthermore, ethiprole exposure led to increased catalase activity and carbonylated protein levels in muscle. Morphometric and pathological analyses of the gills revealed that increasing ethiprole concentration resulted in hyperemia and loss of integrity of the secondary lamellae. Similarly, histopathological analysis of the liver demonstrated higher prevalence of necrosis and inflammatory infiltrates with increasing ethiprole concentration. Altogether, our findings demonstrated that sublethal exposure to ethiprole can trigger a stress response in non-target fish species, which may lead to potential ecological and economic imbalances in Neotropical freshwater systems.

"Fearing the enemy": Growth and stress biomarker responses of sexually reversed Oreochromis niloticus in the presence of aquatic predatory insects.

Fishes can change their physiological responses when threatened by the presence of predators. Such physiological plasticity, however, usually implies costs that may impede organismal development and reproduction and reduce the ability to cope with other biotic and abiotic stresses. Here, we evaluated the growth and stress biomarker responses in sexually reversed Nile tilapia, Oreochromis niloticus, fingerlings indirectly threatened by the presence of the aquatic insect predator Belostoma anurum (Hemiptera: Belostomatidae). We also evaluated whether the presence of B. anurum would affect growth in fingerlings that received food containing the masculinizing hormone 17 α-methyltestosterone. The antioxidant responses were evaluated by measuring the activity of enzymes (e.g., superoxide dismutase, catalase, and glutathione-S-transferase). Oxidative stress biomarkers (e.g., malondialdehyde and nitric oxide) and blood glucose and lactate responses were also evaluated. Our results revealed that predator exposure did not affect growth in O. niloticus fingerlings reared in the presence or absence of the masculinizing hormone. However, sexually reversed tilapia fingerlings significantly increased not only the glucose and lactate blood levels, but also exhibited increased activities of superoxide dismutase and glutathione-S-transferases enzymes when threatened by the presence of B. anurum nymphs. Collectively, our findings indicate that despite not exhibiting reduced growth performance, sexually reversed tilapia fingerlings were physiologically stressed by the presence of the predator, which may reduce their ability to face environmental and abiotic stresses.