This study investigated the effects of hypoxia on oxidative stress response and immune function in mussels Perna perna exposed to air for 6, 12, 24 and 48 h. In air-exposed mussels, the antioxidant enzymes superoxide dismutase (SOD), catalase, and glutathione reductase (GR) activities were lower in gill tissues (24-48 h) and digestive gland (12 h), while the glutathione peroxidase and GR activities were increased in the digestive gland (48 h). In both tissues, aerial exposure promoted a rapid (6 h) and persistent (up to 48 h) increase of glutathione levels. Decreased hemocyte count and viability, as well as increased phagocytic activity and cellular adhesion capacity were detected after prolonged aerial exposure (>12 h). In summary, induction of thiol pools, altered antioxidant enzyme activities, and activation of immune responses were detected in hypoxia exposed brown mussels, indicating hypoxia induced tissue-specific responses in both antioxidant and immune systems.

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Drought can be viewd as a perturbation in running waters and fish are often trapped in isolated pools, where deterioration of water quality may be stressful. We investigated how this extreme condition influences response of oxidative stress biomarkers. The response of the characid Astyanax elachylepis was assessed during the dry and rainy seasons in intermittent and perennial (control) sites in streams from Brazilian savannah (Cerrado). We predicted that the biomarkers would be enhanced in the dry season in intermittent streams only due the environmentally harsh conditions in the few isolated pools that remain filled with water. As predicted, fish from the intermittent stream in the dry season presented higher gill MDA values, indicating greater stress. In the liver, MDA values were higher in the dry season for both intermittent and perennial streams, suggesting a generalized seasonal response. As expected, some antioxidant response enzymes changed in the intermittent sites during the dry season. Therefore, oxidative stress biomarkers vary seasonally, with greater increase in intermittent sites. These evidences contribute for the understanding of the spatio-temporal variation of the fish responses and fish resistance to perturbations by drought in tropical environments.