Assimilation of nitrogen and carbon isotopes from fish diets to otoliths as measured by nanoscale secondary ion mass spectrometry
Assimilation of nitrogen and carbon isotopes from fish diets to otoliths as measured by nanoscale secondary ion mass spectrometry
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通过纳米级二次离子质谱法测量鱼类饮食中氮和碳同位素与耳石的同化
DOI：
10.1002/rcm.8171
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发表时间：
2018
影响因子：
2
通讯作者：
Tseng Yung-Che
中科院分区：
文献类型：
--
作者：
Shiao Jen-Chieh;Shirai Kotaro;Tanaka Kentaro;Takahata Naoto;Sano Yuji;Sung-Yun Hsiao Silver;Lee Der-Chuen;Tseng Yung-Che
[中英文摘要]耳石中碳酸盐结合有机物质的氮和碳稳定同位素比值(δ15N和δ13C值)可以为研究鱼类的生物和生态功能提供信息。正确解释耳石δ15N和δ13C剖面需要了解氮和碳同位素的代谢途径。然而，δ15N和δ13C从饲料到耳石的同位素同化研究很少。方法利用纳米级二次离子质谱仪(NanoSIMS)追踪饲料和耳石之间的每日氮和碳同位素同化。对尼罗罗非鱼(Oreochromis Niloticus)进行14~17d的摄食试验。用纳米SIMS和常规同位素比值质谱仪分别测定了耳石和鱼肌肉中δ15N和δ13C的变化。结果在鱼体内加入15N的藻类后，δ15N值从自然丰度水平突然飙升了1000-2300‰，δ15N值约为2200‰。然而，在投喂试验结束时，鱼肌肉的δ15N值仅增加到约500‰。加入15N和13C的罗非鱼耳石中的δ15N值(3700-14000‰)和中等δ13C值(60-200‰)要高得多，δ15N值为36667‰，δ13C值为272‰。图谱分析显示，在罗非鱼将饲料从未添加添加剂的藻类转移到15N标记的藻类后，耳石生长量中嵌入了15N的亚微米级分布，并有从低到高的δ15N信号。结论上述结果表明，耳石中来自食物的氮和碳同位素在同一天被直接同化。食物是耳石氮同位素的主要来源，在某些情况下是唯一的来源，但对耳石碳同位素只有部分贡献。因此，耳石硬化层中记录的δ15N值可用于确定鱼类的营养水平、食物来源和食性变化。
RATIONALENitrogen and carbon stable isotope ratios (δ15N and δ13C values) of carbonate‐bound organic materials in otoliths can provide information to address the biological and ecological functions of fish. Correct interpretation of otolith δ15N and δ13C profiles requires knowledge of the metabolic routes of nitrogen and carbon isotopes. However, the isotopic assimilation of δ15N and δ13C compositions from diets to otoliths has rarely been investigated.METHODSThis study traced the daily nitrogen and carbon isotopic assimilation between diets and otoliths using nanoscale secondary ion mass spectrometry (NanoSIMS). Isotopically labeled algae (Tetraselmis chui) were fed to tilapia (Oreochromis niloticus) for 14–17 days. NanoSIMS and conventional isotope ratio mass spectrometry were used to measure δ15N and δ13C variations in the otoliths and fish muscle, respectively.RESULTSOtolith δ15N values abruptly surged from natural abundance levels by 1000–2300‰ after the fish ate15N‐spiked algae with δ15N values of approximately 2200‰. However, the δ15N values of fish muscle increased to only approximately 500‰ at the end of the feeding experiment. Much higher δ15N values (3700–14 000‰) and moderate δ13C values (60–200‰) were detected in the otoliths after the tilapia ate15N‐ and13C‐spiked algae with a δ15N value of 36667‰ and a δ13C value of 272‰. Mapping analysis showed sub‐micrometer‐scale distribution of15N embedded in the otolith growth increments with a low‐to‐high δ15N signal after the tilapia shifted diets from non‐spiked to15N‐labeled algae.CONCLUSIONSThese results suggest that otolith nitrogen and carbon isotopes from food were directly assimilated on the same day. Food is the major and in some cases only source of otolith nitrogen isotopes but makes only a partial contribution to otolith carbon isotopes. Therefore, the δ15N values recorded in the sclerochronological layers of the otoliths can be used to determine the trophic levels, food sources and diet changes of fish.