The Effects of Combinations of Limited Ration and Diazinon Exposure on Acetylcholinesterase Activity, Growth, and Reproduction in Oryzias latipes, the Japanese medaka

Environmental contamination can negatively impact fish populations. In addition to acute toxicity leading to death, toxicants can reduce fish growth and lower reproduction. The potential for adverse population level effects of environmental contaminants are estimated from laboratory toxicity tests that most often measure apical endpoints related to growth, survival, and reproduction. The relationships between these endpoints are being evaluated to better predict shifts in fish population demography after exposure to environmental toxicants. Environmental contaminants can also affect fish populations indirectly by reducing prey biomass. However, estimating the combined effects of prey reduction and direct toxicity is difficult and rarely attempted. Here we describe a toxicity test designed to estimate the effect on Japanese medaka of both reduced food and chronic exposure to diazinon, an acetylcholinesterase inhibiting organophosphate pesticide. Fish were reared with limited food ration and/or diazinon exposure through a full life-cycle to assess possible interactions between the two stressors in their effects on growth and reproduction. Diazinon exposure, reduced ration, or combinations of both lowered growth rates and reproductive output of Japanese medaka. Various relationships between the two stressors (diazinon and ration) and growth and reproduction were modeled. These results inform fish models being developed by EPA to predict population consequences of chemical exposures.

环境污染可对鱼类种群产生负面影响。除引发死亡的急性毒性作用外，有毒物质还会抑制鱼类生长、降低其繁殖能力。环境污染物对种群层面的潜在不利影响，通常通过实验室毒性试验进行评估，这类试验多测定与生长、存活及繁殖相关的顶端终点（apical endpoints）。研究人员正评估这些顶端终点间的关联，以更精准地预测鱼类种群在暴露于环境有毒物质后其种群动态的变化。环境污染物还可通过降低猎物生物量，对鱼类种群产生间接影响。然而，同时估算猎物减少与直接毒性的联合效应颇具难度，相关研究也鲜有开展。本研究描述了一项毒性试验，旨在评估食物配额受限与慢性暴露于二嗪农（diazinon，一种抑制乙酰胆碱酯酶的有机磷农药）对日本青鳉的综合影响。研究人员在全生命周期内对鱼类进行限量投喂及/或二嗪农暴露处理，以探究这两种胁迫因子对鱼类生长与繁殖的交互效应。二嗪农暴露、食物配额减少，以及二者的联合处理，均会降低日本青鳉的生长速率与繁殖输出。研究人员对两种胁迫因子（二嗪农与食物配额）与生长、繁殖间的多种关联进行了建模分析。上述研究结果可为美国环境保护署（EPA）正在开发的、用于预测化学暴露对种群影响的鱼类种群模型提供参考依据。