大黄鱼早期发育过程对甲基汞胁迫的响应及其机制研究

Mercury is one of the most toxic metals in marine environments. It causes various damages to the central nervous system and endocrine system of fish as well as disrupt vital functions such as reproduction, osmoregulation, orientation, foraging, predator recognition and communication in fish. Mercurials could be biologically transformed into more toxic and bioavailable organic form-methylmercury. However, studies have been more carried out to investigate the toxicity of inorganic mercury than that of organic mercury. Early life stages (ELS) are of primary importance to fish population dynamics due to the intense mortality during the embryonic and larval periods. Fish embryos and larvae are particularly sensitive to natural and anthropogenic origin stressors including mercury exposure. To our knowledge, there is little literature about the responses of ELS of marine fish species to methylmercury, especially about the changes of its metabolic products and antioxidants. In this research program, biochemical and metabolomics techniques are used to investigate the toxicological effects of methylmercury exposure on the development and growth of large yellow croaker embryos and larvae in order to: (1) evaluate the accumulation dynamics of methylmercury in different stages and tissues of embryos and larvae, (2) investigate whether their antioxidative system during embryogenesis and larval development are sensitive bioindicators for methylmercury exposure, and (3) explore the biochemical and metabolic mechanism underlining methylmercury toxicity to the ELS of marine fish.

甲基汞(MeHg)是汞在海洋生物体内的主要赋存形态，对海洋生物神经系统、内分泌系统具有极强毒性，但迄今甲基汞对海水鱼类早期发育过程毒理效应及机制的研究十分薄弱。本项目选取大黄鱼作为研究对象，综合运用代谢组学和生物化学方法系统研究甲基汞对其胚胎和仔稚鱼的毒理效应，阐明甲基汞在大黄鱼各组织中的蓄积动力学特征，解析大黄鱼早期发育过程抗氧化防御系统和内源性代谢物对甲基汞胁迫的响应方式。项目探索性地将代谢组学技术应用于污染物对海水鱼类早期生活阶段毒理效应的研究中，旨在从代谢水平揭示甲基汞对海水鱼类早期生活阶段的致毒机制。本研究可为代谢组学技术在生态毒理学中的应用提供研究实例，同时为科学认识近海污染胁迫下海洋生物资源的衰退机制提供理论依据。

鱼类早期生活阶段 (Early life stages, ELS) 又称为鱼类早期生活史 (分为胚胎期、仔鱼期和稚鱼期)，是其整个生活史中对外界环境最敏感的阶段。研究表明，低浓度污染物在不足以对成鱼造成明显毒害作用时，可能会引起胚胎和仔稚鱼的毒性反应，因此研究污染物对鱼类早期生活阶段的毒理效应和机制是揭示污染物对水生生态系统潜在风险的有效途径。本项目研究了甲基汞对大黄鱼 (Pseudosciaena crocea)早期发育过程的生理、生化和代谢等层面的影响，并揭示了低浓度污染条件下其致毒机制，相关结果可为生态风险评价、生态养殖海水水质标准的制定提供科学依据和理论参考。结果表明，甲基汞对大黄鱼胚胎的48 h LC50值为28.39（21.33-31.98，95%置信区间）μg L-1，对仔鱼的96 h LC50值为9.28（4.41-14.49）μg L-1。胚胎的累积孵化率随着溶液中甲基汞浓度的升高而显著降低，20.0 μg L-1组孵化率显著低于对照组；甲基汞暴露也显著影响仔鱼畸形率；其中10.0和20.0 μg L-1组仔鱼畸形率比对照组显著增加。实验中观察到的仔鱼畸形类型包括脊柱畸形、尾部弯曲、尾部退化、围心腔水肿、出血和鳍膜腐烂等。不过，甲基汞暴露对仔鱼体长并无显著影响。甲基汞暴露对大黄鱼幼鱼抗氧化酶系（SOD、CAT、GSH、GPx、GST）和脂质过氧化物（MDA含量）均有显著影响。实时定量PCR检测发现经甲基汞暴露的大黄鱼组织中TCTP, GST3, Hsp70, Hsp27 以及 HIF-1ɑ 的表达均呈现和浓度相关的增加趋势。此外，本项目利用代谢组学方法筛选出30种可以反映甲基汞污染造成大黄鱼显著改变的代谢物，后续将继续收集样本对代谢物进行MRM定量检测分析并构建用于预测甲基汞污染大黄鱼早期病理状态模型并验证。项目的实施可为深入了解甲基汞对鱼类早期发育的毒理效应及其内在机制提供科学依据和理论参考。