Fish biomarker responses to perturbation by drought in streams

ABSTRACT 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.

摘要：干旱可视为流水生态系统的一类扰动事件，鱼类常会被困于残存积水的孤立水洼中，此时水质恶化将使其承受显著胁迫压力。本研究探讨了该极端环境条件对鱼类氧化应激生物标志物响应的影响。以巴西塞拉多(Cerrado)稀树草原溪流中的间歇性溪流与永久性溪流（对照样点）为研究对象，我们于旱季与雨季分别检测了脂鲤科(characid)物种Astyanax elachylepis的氧化应激响应。我们提出假设：仅在间歇性溪流的旱季，由于孤立水洼的严苛环境条件，其氧化应激生物标志物的表达水平会升高。实验结果与预测一致：旱季间歇性溪流中的鱼类鳃组织丙二醛(MDA, malondialdehyde)水平显著升高，表明其胁迫程度更强；而在肝脏组织中，无论间歇性还是永久性溪流，旱季的MDA水平均更高，提示存在普遍性的季节响应模式。同时，旱季间歇性样点的部分抗氧化应答酶活性亦发生了显著变化，符合预期。综上，氧化应激生物标志物呈现季节性变化规律，且在间歇性溪流样点中的上调幅度更为显著。本研究结果可为理解热带环境中鱼类对干旱扰动的响应时空变异及其抗胁迫能力提供理论参考。