Freshwater cyanobacterial harmful algal blooms (CyanoHABs) caused by algae in the genus Microcystis have been increasing in frequency and severity in recent decades. Microcystis blooms threaten aquatic organisms through effects associated with the rapid increase of biomass and the production of the hepatotoxin microcystin (MC) by toxic strains. Among fish, effects of blooms are likely to be more severe for early life stages, and physiological impacts on this life stage could significantly impact recruitment and fish populations. This study explores the effects of Microcystis blooms on the development of fish using the model organism, the Japanese medaka (Oryzias latipes), under realistic exposure conditions. Medaka embryos were exposed to natural blooms collected from New York City (USA) lakes, lab cultures of Microcystis, and MC-LR solutions. Field collected samples were more toxic than lab cultures (even when compared at the same algal density or MC concentration), causing decreased survival, premature time to hatch, reduced body length, yolk sac edema, and decreased heart rate, while lab culture exposures only resulted in bradycardia. Heart rate was the most sensitive endpoint measured, being depressed in embryos exposed to both lab cultures and field collected blooms. Generalized linear model analysis indicated bradycardia was statistically associated with both cell densities of blooms and MC concentrations, while single factor analysis indicated that MC concentrations had a stronger correlation compared to cell densities. However, MC exposure could not fully explain the effects observed, as exposures to MC-LR solutions alone were not able to reduce heart rate as severely as algal exposures. Collectively, these experiments indicate that factors beyond exposure to MC or even isolated Microcystis strains influence heart rate of fish exposed to Microcystis blooms. Enhanced mortality, depressed heart rate, and abnormal development observed in response to environmentally realistic exposures of Microcystis blooms could affect success of fish at both individual or population levels.

近几十年来，由微囊藻属中的藻类引起的淡水蓝藻有害藻华（CyanoHABs）的频率和严重性一直在增加。微囊藻的开花通过与生物量的快速增加和有毒菌株产生的肝毒素微囊藻毒素（MC）相关的效应威胁着水生生物。在鱼类中，绽放的影响在生命的早期阶段可能更为严重，而对这一生命阶段的生理影响可能会极大地影响捕捞和鱼类种群。这项研究使用模式生物日本organism（Oryzias latipes）探索微囊藻开花对鱼类发育的影响），在现实的曝光条件下。将Medaka胚胎暴露于从纽约市（美国）湖泊收集的自然开花中，这些细菌是微囊藻的实验室培养物和MC-LR解决方案。田间采集的样品比实验室培养物更具毒性（即使在相同的藻类密度或MC浓度下进行比较），也会导致存活率降低，孵化提前，体长减少，卵黄囊浮肿和心率降低，而仅暴露于实验室培养物导致心动过缓。心率是所测量的最敏感的终点，在暴露于实验室培养物和田间开花的胚胎中均降低了心率。广义线性模型分析表明，心动过缓与绽放的细胞密度和MC浓度在统计学上相关，而单因素分析表明MC浓度与细胞密度相比具有更强的相关性。但是，MC暴露无法完全解释所观察到的影响，因为仅暴露于MC-LR溶液无法像藻类暴露一样严重地降低心率。总的来说，这些实验表明，超出暴露于MC甚至是孤立的因素微囊藻菌株影响暴露于微囊藻水华的鱼的心率。在环境上现实暴露微囊藻水华后，观察到死亡率提高，心律降低和发育异常，可能会影响个体或种群水平的鱼类成功。