Larval yellow perch locations during locomotion assays after exposure to MeHg and PCB126

Fish swimming behavior is a commonly measured response in aquatic
ecotoxicology because behavior is considered a whole organism-level effect
that integrates many sensory systems. Recent advancements in animal
behavior models, such as hidden Markov chain models (HMM), suggest an
improved analytical approach for toxicology. Using both new and
traditional approaches, we examined the sublethal effects of PCB126 and
methylmercury on yellow perch (YP) larvae (Perca flavescens) using three
doses. Both approaches indicate larvae increase activity after exposure to
either chemical. The middle methylmercury-dosed larvae showed multiple
altered behavior patterns. First, larvae had a general increase in
activity, typically performing more behavior states, more time swimming,
and more swimming bouts per second. Second, when larvae were in a slow or
medium swimming state, these larvae tended to switch between these states
more often. Third, larvae swam slower during the swimming bouts. The upper
PCB126-dosed larvae exhibited a higher proportion and a fast swimming
state, but the total time spent swimming fast decreased. The middle
PCB126-dosed larvae transitioned from fast to slow swimming states less
often than the control larvae. These results indicate that developmental
exposure to very low doses of these neurotoxicants alters YP larvae
overall swimming behaviors, suggesting neurodevelopment alteration.

鱼类游泳行为是水生生态毒理学中常见的观测响应指标，这是因为行为可被视为整合了多种感官系统的整体生物体级效应。近年来动物行为模型（如隐马尔可夫链模型（Hidden Markov Chain Model, HMM））的进展，为毒理学研究提供了更优化的分析手段。本研究同时采用新兴与传统方法，设置三个剂量梯度，探究了多氯联苯126（PCB126）与甲基汞对黄鲈（Yellow Perch, YP，Perca flavescens）幼鱼的亚致死效应。两类分析方法均显示，暴露于任一受试化学物后，黄鲈幼鱼的活动量均有所提升。

甲基汞中剂量组的黄鲈幼鱼呈现出多种行为模式改变：其一，幼鱼整体活动量提升，具体表现为行为状态种类更多、游泳时长更长、每秒游泳频次更高；其二，当幼鱼处于慢速或中速游泳状态时，其在两类状态间的切换频率显著升高；其三，幼鱼在单次游泳过程中的游速有所降低。

多氯联苯126高剂量组的黄鲈幼鱼，其快速游泳状态的占比更高，但快速游泳的总时长却有所减少。多氯联苯126中剂量组的幼鱼，其从快速游泳状态切换至慢速游泳状态的频率低于对照组幼鱼。

上述结果表明，发育期暴露于极低剂量的这类神经毒物，会改变黄鲈幼鱼的整体游泳行为，提示其神经发育受到了影响。