Ernst Bernhard, Hoeger Stefan J, O'brien Evelyn, Dietrich Daniel R
Environmental Toxicology, University of Konstanz, P.O. Box X-918, D-78457 Konstanz, Germany.
Aquat Toxicol. 2007 Apr 20;82(1):15-26. doi: 10.1016/j.aquatox.2007.01.007. Epub 2007 Feb 1.
Planktothrix rubescens belongs to the most ubiquitous cyanobacterial species in mesotrophic and oligotrophic lakes in the pre-alpine regions. In most of these lakes, coregonids are among the dominant species of the ichthyofauna with great importance for the professional fishery. A possible link between the occurrence of toxic Planktothrix blooms and the recurrent slumps in coregonid yields has been suggested. Indeed, acute toxic effects of microcystins and other cyanobacterial toxins have been shown for various fish species. However, chronic exposure scenarios appear to be more common and thus more environmentally realistic than acute intoxications. The aim of this study was therefore to investigate the physiological stress response and organ pathology in coregonids sub-chronically exposed to ambient water containing low, medium and high P. rubescens densities, known to be typical of pre-alpine lakes. Coregonid hatchlings were exposed in four tanks containing 0 (sham-control) and approximately 1500 (low), 15,000 (medium) and 55,000 (high) P. rubescens cells/ml for up to 28 days. Temperature, oxygen concentration, pH-value, P. rubescens cell density and microcystin concentration were recorded and the fish were observed for behavioural changes and examined for parasite infestations. Gill ventilation rates, general condition factors and mortalities were determined and liver, kidney, gut and gill were assessed histopathologically and immunhistologically. Depending on the cell density, exposed fish showed behavioural changes, including increased ventilation rates possibly representing a physiological stress response. Susceptibility to ectoparasitic infestation and increased mortality in exposed fish suggested P. rubescens associated effects on fish fitness. Histopathological alterations in liver, gastrointestinal tract and kidney, which were also immunopositive for microcystin suggested causality of tissue damage and the presence of microcystins. In contrast, observed gill pathology appeared to result primarily from mechanical abrasion and irritation due to ectoparasitic infestation. The current exposure experiment confirmed the hypothesis that subchronic and chronic exposure to low cyanobacterial cell densities and hence microcystins can exacerbate physiological stress and sustained pathological alterations in exposed coregonids. The study therefore supports the theory that P. rubescens blooms may be causal to the observed weight reduction and hence fitness of coregonids in pre-alpine lakes such as Lake Ammersee (Germany).
红颤藻是前阿尔卑斯地区中营养和贫营养湖泊中最常见的蓝藻物种之一。在这些湖泊中的大多数，白鲑是鱼类区系中的优势物种之一，对专业渔业非常重要。有人提出有毒颤藻水华的出现与白鲑产量的反复下降之间可能存在联系。事实上，微囊藻毒素和其他蓝藻毒素对各种鱼类都有急性毒性作用。然而，慢性暴露情况似乎比急性中毒更为常见，因此在环境中更符合实际情况。因此，本研究的目的是调查亚慢性暴露于含有低、中、高红颤藻密度的环境水中的白鲑的生理应激反应和器官病理学，已知这种情况在该地区的前阿尔卑斯湖泊中很典型。将白鲑幼鱼暴露在四个水箱中，分别含有0（假对照）、约1500（低）、15000（中）和55000（高）个红颤藻细胞/毫升，暴露时间长达28天。记录温度、氧气浓度、pH值、红颤藻细胞密度和微囊藻毒素浓度，并观察鱼的行为变化，检查是否有寄生虫感染。测定鳃通气率、一般状况因子和死亡率，并对肝脏、肾脏、肠道和鳃进行组织病理学和免疫组织学评估。根据细胞密度，暴露的鱼表现出行为变化，包括通气率增加，这可能代表一种生理应激反应。暴露的鱼对外寄生感染的易感性增加和死亡率上升表明红颤藻对鱼的健康有影响。肝脏中的组织病理学改变，胃肠道和肾脏中微囊藻毒素免疫阳性表明组织损伤与微囊藻毒素的存在存在因果关系。相比之下，观察到的鳃病理学似乎主要是由于外寄生感染引起的机械磨损和刺激导致的。目前的暴露实验证实了这样一个假设，即亚慢性和慢性暴露于低蓝藻细胞密度以及因此的微囊藻毒素会加剧暴露的白鲑体内的生理应激和持续的病理改变。因此，该研究支持了这样一种理论，即红颤藻水华可能是导致在德国阿默湖等前阿尔卑斯湖泊中观察到的白鲑体重减轻以及健康状况下降的原因。
