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：干旱可被视为溪流生态系统中的扰动事件，鱼类常会被困于孤立水洼中，此处水质恶化会带来显著胁迫压力。本研究探究了该极端环境条件对氧化应激生物标志物（oxidative stress biomarkers）响应的影响。本研究以巴西塞拉多（Cerrado）热带稀树草原流域的溪流为研究对象，在旱季与雨季分别对间歇性溪流与永久性溪流（对照样地）中的脂鲤科（Characidae）鱼类*Astyanax elachylepis*的响应进行评估。我们提出假说：仅在间歇性溪流的旱季，由于仅剩的少量积水孤立水洼的环境条件更为严苛，其氧化应激生物标志物的水平会升高。正如实验预期，旱季间歇性溪流中的鱼类鳃组织丙二醛（Malondialdehyde, MDA）水平更高，表明其受到的胁迫更强。而在肝脏组织中，间歇性与永久性溪流的鱼类在旱季的MDA水平均更高，这提示存在一种普遍性的季节响应模式。与预期一致，旱季间歇性样地中的部分抗氧化应答酶活性发生了显著变化。因此，氧化应激生物标志物的表达存在明显的季节动态变化，且在间歇性溪流样地中的升高幅度更为显著。本研究结果有助于加深对热带环境中鱼类响应干旱扰动的时空变异规律及其抗逆能力的理解。