南极鱼类耳石微化学研究进展

南大洋生态系统的特异性极为显著,栖息在该海域的鱼类资源也存在着较为明显的本地特征以及对极端环境的适应能力。耳石微化学记录了鱼类完整生活史过程,可以揭示鱼类生活史过程中经历的时空变化。利用耳石中微化学元素,可以解决鱼类生态学中,如产卵场和洄游路径推测、生活史过程重建、种群划分等一系列实际问题。随着耳石微化学技术的不断完善,耳石微化学研究在海洋鱼类中的应用越来越广泛。相对于其他海区,目前南大洋鱼类耳石微量元素研究相对较少,仅涉及3科11种鱼类,约占南极鱼类总数的5%,且主要研究集中于商业性价值较高的鱼类,包括小鳞犬牙南极鱼(Dissostichus eleginoides)、鳞头犬齿南极鱼(D.mawsoni)、次南极电灯鱼(Electrona carlsbergi)、南极电灯鱼(E.antarctica)、裘氏鳄头冰鱼(Champsocephalus gunnari)和侧纹南极鱼(Pleuragramma antarcticum)等11种南极鱼类。耳石微化学研究主要集中在鱼类栖息环境重塑、种群划分以及生活史过程重建等三个方面。今后,更为先进的技术,如微计算断层扫描技术以及人工智能等,将为南极鱼类耳石微化学研究提供重要的支撑。考虑到南大洋鱼类多数具有典型的环南极分布特征,可通过耳石微化学技术进一步探究鱼类产卵场推定以及环极连通性等,并进一步阐释南极鱼类的生物-环境相互作用,相关工作也将为南大洋鱼类资源的开发利用及有效管理提供支撑信息。     

耳石微化学在海洋鱼类洄游类型和种群识别研究中的应用

水环境中化学元素会有规律性地在鱼类耳石上沉积。耳石可作为生境"指纹"标签的独特属性使其更能有效地应用于鱼类资源时空动态的研究。现针对了解较少的海洋鱼类耳石微化学所涉及的主要元素,综述了Sr:Ca值和多元素组合在这些鱼类生活史重建、迁移模式反演和资源种群识别上的研究进展。进展显示,海水中Sr:Ca值的微小变化可以通过在海洋鱼类耳石中的元素积累而放大,有助于把握鱼类的种间差异或种内不同发育阶段个体的差异。耳石中多元素组合的分析,亦可有效解释海洋鱼类生活史不同阶段间的生境转换和洄游特征,甚至"破译"复杂的资源种群结构。耳石微化学在海洋鱼类养护研究上具有极大的潜力,相关研究需要在我国得到更多的重视和更大的支持。     

鱼类耳石微结构特征的研究与应用

鱼类耳石的结构与组成相当稳定,可能反映鱼类的生长情况及一生所经历的环境变化.自20世纪70年代以来,耳石微结构研究领域迅速发展,成为研究鱼类早期生活史的基础.耳石微结构的检测与分析(Otolith microstructure examination and analysis)已成为当今鱼类生态学及渔业生物学研究中的一项重要而公认的技术1,为准确研究鱼类的种群生态学特征提供了新途径,不仅具有一定的理论意义,而且有较广泛的应用前景.       

秘鲁外海茎柔鱼摄食洄游的稳定同位素研究

茎柔鱼是具有高度洄游性的中上层头足类,是生态系统中的关键物种,也是我国远洋渔业重要捕捞对象之一.了解掌握茎柔鱼摄食及洄游信息有助于对其资源进行更合理利用.头足类内壳是一良好的信息载体,其生长发育具有不可逆性且生长贯穿整个生活史过程,包含了头足类生活史过程中的全部信息.本研究通过对秘鲁外海茎柔鱼耳石日龄进行鉴定,建立其内壳叶轴生长方程,根据该生长方程对内壳叶轴进行连续切割,测定其碳、氮稳定同位素比值,并初步分析了其在生长发育过程中的食性转换和洄游习性.结果表明: 茎柔鱼个体在出生180 d后开始洄游活动,且营养层次存在下降趋势.证明了内壳连续取样分析茎柔鱼个体摄食习性和栖息地变化的可行性.     

基于形态分析探究鳞头犬牙南极鱼各生活史阶段耳石形态变化

鳞头犬牙南极鱼为南极最为重要的底层鱼类,具有重要的生态作用和极高的商业价值,鱼类耳石形态随着生活史过程的推移有所差异,故耳石形态分析可用于推断鳞头犬牙南极鱼的生活史过程。本研究利用采集自南极罗斯海、阿蒙森海、威德尔海及拉扎列夫海120尾分属4个生活史阶段的鳞头犬牙南极鱼耳石,结合传统测量分析与椭圆傅里叶分析两种形态学研究方法,对其各生活史阶段耳石形态的差异进行研究。结果表明: 鳞头犬牙南极鱼各生活史阶段耳石形态存在差异,随着生活史过程的推移,耳石的变化趋势为整体上由轮廓平滑、复杂度较低向轮廓曲折、高度复杂化转变,且纵轴方向增长速度低于横轴方向,翼叶等特征部位变化显著。针对耳石形态的线性判别分析结果显示,椭圆傅里叶分析判别值较高,为85.4%,而传统测量分析判别值较低,为71.9%,表明相较于传统测量分析,椭圆傅里叶分析更具优势。     

长江安庆江段刀鲚耳石微化学及洄游生态学意义

刀鲚(Coilia nasus)属辐鳍鱼纲、鲱形目、鳀科,是我国长江下游一种传统的名贵经济鱼类。长江安徽江段为刀鲚的主要分布区之一,但近年来由于人类活动干扰、栖息地衰退及过捕等原因,资源量急剧下降。近期发布的《国家重点保护野生动物名录》水生野生动物调整方案已拟将刀鲚列入国家二级重点野生动物保护名录。为客观了解长江安庆江段刀鲚的生境"履历"及探讨其洄游史,利用X射线电子探针微区分析技术对2008年7月捕获于长江安庆江段的10尾刀鲚(均为传统意义上的长颌鲚)进行了耳石微化学研究。结果表明:这些个体均具典型的溯河洄游习性。从耳石核心到边缘定量线分析结果表明,耳石的沉积过程中元素Sr/Ca比值波动显著,不仅有对应淡水生境的低值(3)阶段,还具有对应河口半咸水、海水生境的高值(3)阶段。这种现象亦得到了16色Sr元素面分布分析结果的印证。根据耳石淡水系数、Sr/Ca比值高低波动特征及Sr元素面分布图谱的差异性可以将这些刀鲚分为3种淡-海水生境转换生活史类型。这种现象明显地反映出长江安庆江段刀鲚的群体具有个体组成和洄游模式的多样性。     

基于耳石微化学的乌苏里白鲑生境履历分析

为了分析乌苏里白鲑(Coregonus ussuriensis Berg)的洄游生态类型及生境履历, 采用X射线电子探针微区分析技术(EPMA)研究了2013年12月、2014年1月黑龙江干流2尾和松花江干流2尾乌苏里白鲑矢耳石的锶(Sr)、钙(Ca)元素微化学特征。定量线分析结果显示, 乌苏里白鲑耳石锶钙比值(Sr/Ca×103)波动显著, 具有对应淡水生活的低值区(小于5), 而且还有对应咸水生活的高值区(大于10), 显示了乌苏里白鲑的溯河洄游履历; 耳石元素面分析结果也显示乌苏里白鲑的淡水-咸水洄游的特征。结合耳石年轮特征分析, 乌苏里白鲑具有年度(季节)洄游特征, 部分群体有规律在淡水-咸水中季节洄游, 不同个体在淡水、咸水之间停留时间存在较大差异。研究表明, 乌苏里白鲑伴随着季节性洄游特征, 具有江海或者淡水-河口之间洄游的履历。     

四川裂腹鱼耳石碳、氧稳定同位素特征

为探讨耳石碳(δ¹³C)、氧(δ¹⁸O)稳定同位素在淡水鱼类群体识别中的作用,本研究以养殖条件下不同年龄组四川裂腹鱼为对象,采用稳定同位素质谱仪进行碳、氧同位素测定,揭示耳石中碳、氧稳定同位素特征,探讨其与环境间的关系. 结果表明:1⁺龄四川裂腹鱼δ¹³C和δ¹⁸O值均与耳石质量无显著相关关系,但在微耳石和星耳石之间存在显著差异;不同年龄四川裂腹鱼微耳石δ¹³C和δ¹⁸O平均值分别为(-9.58±0.06)‰、(-8.33±0.17)‰,其在雌雄个体之间均无显著性差异,但在不同年龄组间存在显著差异. 耳石δ¹⁸O和δ¹³C的关联分析能有效区分四川裂腹鱼不同养殖年龄群体,可作为一种识别淡水鱼类养殖群体的手段.     

鲬鱼耳石形态多样性研究

硬骨鱼类的矢耳石在物种间存在明显的形态差异, 常常被用来进行鱼类的分类研究13。例如, 张国华等通过形态的观察与描述对鲤科鱼类的耳石进行了区分4; 潘晓哲等采用耳石形状指数方法对 属鱼类进行了鉴别5; 王英俊用傅里叶方法研究了多种鱼类耳石, 并记录了它们之间的形态差异6。因为耳石坚硬不易被消化, 所以在水生动物的食性研究中, 利用耳石进行胃含物内种类鉴定可大大提高工作效率与准确性。此类研究也并不鲜见, 如张波等对黄海重要饵料鱼类的耳石形态做了较为详细的描述7, Fitch, et al.依据鲸类胃含物中的鱼类耳石形态鉴定了捕食鱼类的种类进而对其食性进行了研究8。另外, 不同生活环境能够导致耳石生长和形态的差异, 这也使其成为了群体差异研究的有效手段912。       

洞庭湖中是否存在溯河洄游型刀鲚

利用电子探针微区分析(EPMA)技术, 分析了2018年8月采自湖南省岳阳市洞庭湖畔水产市场2尾刀鲚(Coilia nasus)干制个体的矢耳石中锶和钙微化学特征。定量线分析结果显示, 2尾样本的耳石锶钙比值(Sr/Ca×1000)波动显著, 从耳石核心到边缘可分别出现对应淡水生境的锶钙比值<3的低值区, 对应于半咸水生境的3—7高值区和再次为对应于淡水生境<3的低值区。面分布分析结果更直观显示两尾刀鲚个体的耳石从核心到边缘对应于不同盐度生境的锶含量变化图谱, 即从耳石核心到边缘可分别出现对应于淡水生境的蓝色区域, 对应长江口外半咸水生境的黄绿色区域和再次对应于淡水生境的蓝色区域。这种淡水-半咸水-淡水的生境转换显示出了上述个体的典型溯河洄游生活史“履历”。研究显示目前距长江河口约1400 km的洞庭湖中仍可能存在溯河洄游型刀鲚个体。     

Significance of otolith calcium carbonate crystal structure diversity to microchemistry studies

Otoliths, calcium carbonate (CaCO₃) ear stones of fish, contain a wealth of information about fish life and environmental history yet the CaCO₃ polymorph form the otolith is made of is a critical, but seldom considered, piece of information during otolith analysis. Otolith trace element chemistry data increasingly informs management decisions, but recent work has shown that CaCO₃ polymorphs—aragonite, vaterite, and calcite—can bear on incorporation of trace elements in a non-trivial way. Most fishes are thought to have otoliths of the aragonite CaCO₃ form, but this construct is potentially outdated with many recent literature reports showing otherwise. Our study used previously unpublished neutron diffraction data and reports from published literature to address three objectives: (1) summarize the relative effects of otolith CaCO₃ polymorphism on otolith microchemistry, (2) summarize reports of otolith polymorphs to gain a better understanding of the extent of non-aragonite otoliths among fishes, (3) outline future research needed to align interpretations of microchemistry with our current understanding of otolith polymorph diversity. We found that while aragonite otoliths are the most common, so are exceptions. For example, the ostensibly rare (among species) CaCO₃ form vaterite was reported in at least some otoliths of 40% of the species surveyed. Our work suggests that examination of the CaCO₃ polymorph composition of otoliths should become more common particularly in studies where results will or may be used to inform management decisions. Future research should work to attribute controls on otolith CaCO₃ polymorph expression using a combination of -omics and material characterization approaches to enrich the life history and environmental information output from otoliths and increase our understanding of the assumptions made in otolith trace element chemistry studies.

     

Can otolith elemental chemistry retrospectively track migrations in fully marine fishes?

Otolith microchemistry can provide valuable information about stock structure and mixing patterns when the magnitude of environmental differences among areas is greater than the cumulative influence of any vital effects. Here, the current understanding of the underlying mechanisms governing element incorporation into the otolith is reviewed. Hard and soft acid and base (HSAB) theory is employed to explore the differences in chemical behaviours, distributions and affinities between elements. Hard acid cations (e.g. Mg(2+) , Li(+) and Ba(2+) ) tend to be less physiologically influenced and accepted more readily into the otolith crystal lattice but are relatively homogeneous in seawater. Soft acid cations (e.g. Zn(2+) and Cu(2+) ) on the other hand, exhibit more varied distributions in seawater, but are more likely to be bound to blood proteins and less available for uptake into the otolith. The factors influencing the geographical distribution of elements in the sea, and their incorporation into the otoliths of marine fishes are reviewed. Particular emphasis is placed on examining physiological processes, including gonad development, on the uptake of elements commonly used in population studies, notably Sr. Finally, case studies are presented that either directly or indirectly compare population structuring or movements inferred by otolith elemental fingerprints with the patterns indicated by additional, alternative proxies. The main obstacle currently limiting the application of otolith elemental microchemistry to infer movements of marine fishes appears to lie in the largely homogeneous distribution of those elements most reliably measured in the otolith. Evolving technologies will improve the discriminatory power of otolith chemistry by allowing measurement of spatially explicit, low level elements; however, for the time being, the combination of otolith minor and trace element fingerprints with alternative proxies and stable isotopic ratios can greatly extend the scope of migration studies. Among the otolith elements that routinely occur above instrument detection limits, Ba, Mn and Li were deemed the most likely to prove reliable geographic markers in marine species.     

Otolith trace element and stable isotopic compositions differentiate fishes from the Middle Mississippi River, its tributaries, and floodplain lakes

Naturally occurring stable isotope and trace elemental markers in otoliths have emerged as powerful tools for determining natal origins and environmental history of fishes in a variety of marine and freshwater environments. However, few studies have examined the applicability of this technique in large river-floodplain ecosystems. This study evaluated otolith microchemistry and stable isotopic composition as tools for determining environmental history of fishes in the Middle Mississippi River, its tributaries, and floodplain lakes in Illinois and Missouri, USA. Fishes were collected from 14 sites and water samples obtained from 16 sites during summer and fall 2006 and spring 2007. Otolith and water samples were analyzed for stable oxygen isotopic composition (δ¹⁸O) and concentrations of a suite of trace elements; otoliths were also analyzed for carbon isotopic composition (δ¹³C). Tributaries, floodplain lakes, and the Mississippi and Lower Missouri Rivers possessed distinct isotopic and elemental signatures that were reflected in fish otoliths. Fish from tributaries on the Missouri and Illinois sides of the middle Mississippi River could also be distinguished from one another by their elemental and isotopic fingerprints. Linear discriminant function analysis of otolith chemical signatures indicated that fish could be classified back to their environment of capture (Mississippi River, floodplain lake, tributary on the Illinois or Missouri side of the Mississippi River, or lower Missouri River) with 71–100% accuracy. This study demonstrates the potential applicability of otolith microchemistry and stable isotope analyses to determine natal origins and describe environmental history of fishes in the Middle Mississippi River, its tributaries, and floodplain lakes. The ability to reconstruct environmental history of individual fish using naturally occurring isotopic markers in otoliths may also facilitate efforts to quantify nutrient and energy subsidies to the Mississippi River provided by fishes that emigrate from floodplain lakes or tributaries.     

Same habitat,different species: otolith microchemistry relationships between migratory and resident species support interspecific natal source classification

We tested the hypothesis that otolith trace elemental signatures (microchemistries) of mottled sculpin Cottus bairdi, slimy sculpin C. cognatus, and juvenile coho salmon Oncorhynchus kisutch were predictive of those of juvenile steelhead O. mykiss across many sites within the Lake Michigan basin. Laser ablation inductively coupled plasma mass spectrometry was used to generate otolith microchemistry signatures for each individual fish. For each species pair, statistical correlations of mean otolith concentrations of Mg, Mn, Cu, Zn, Sr, Ba, and Pb for each site were estimated. Linear equations describing these relationships were used to transform juvenile steelhead otolith microchemistry data to those of each of the other species. Transformed otolith microchemistry data were subjected to random forest classifications developed for mottled sculpin, slimy sculpin, and juvenile coho salmon to assess interspecific natal source assignment accuracies. Steelhead otolith concentrations of Sr were significantly correlated with those of each of the other species, whereas otolith concentrations of Ba and Mn were significantly correlated among some species pairs, but not others. Natal source assignment accuracies of juvenile steelhead to site and watershed generally decreased when otolith microchemistry data were transformed to those of mottled sculpin, slimy sculpin, and coho salmon. Miss-assigned fish often classified into nearby watersheds within larger hydrologic units, leading to higher assignment accuracies at coarser geographical resolutions (75–97% correct assignment to hydrologic unit for each species). These findings suggest that applications of otolith microchemistry data may extend beyond the species from which they are collected.     

What otolith microchemistry and stable isotope analysis reveal and conceal about anguillid eel movements across salinity boundaries

Otolith microchemistry studies indicate that growth-phase (yellow stage) anguillid eels commonly shift at irregular intervals between fresh and saline waters, but this technique has not detected regular seasonal migrations across salinity zones. We tested the ability of otolith microchemistry and stable isotope analysis to detect migrations of American eels (Anguilla rostrata) between salinity boundaries in two small stream–estuary systems in Canada’s Bay of Fundy. Although the two methods showed concordant classifications of recent residence history, most eels caught in fresh water in spring (68.8–89.7 %) and fall (78.8–83.3 %) showed microchemical and isotopic signatures that reflected occupancy of saline waters. These eels were classified as migrants which had summered in saline waters and then migrated to freshwater wintering grounds where they retained their saline signatures. In summer, most eels (85.0–100.0 %) captured in fresh and saline water had recent microchemical and isotopic signatures matching the habitat of capture. Our results suggest that lifetime otolith microchemistry profiles are unable to detect eel wintering migrations, a failure that is likely due to winter depression of otolith accretion. Elucidation of seasonal eel movements requires cross-seasonal and cross-site sampling for the microchemistry and stable isotope methods, or tagging studies. Seasonal saline–fresh eel migrations may be more common than previously appreciated, underlining the need for conservation of both habitats, and connectivity between the two.     

Mediterranean juvenile bluefin tuna: life history patterns

As there is a lack of information on the growth and migrations of bluefin tuna, information about them was gathered using the structural and chemical characteristics of their otoliths and mercury levels in body tissues as indicators of physiological and habitat characteristics. The otoliths of juvenile tuna caught in the Spanish Mediterranean littoral were studied. Otolith increments, assumed to be formed daily, were enumerated. Measurements by wavelength dispersive electron microprobe confirmed the presence of strontium in otolith tissue, and an inverse relationship between strontium/calcium (Sr/Ca) concentration ratio and temperature is suggested. Electron microprobe analyses combined with daily increment analyses of otoliths provided life history profiles for individual fish. Additional Sr/Ca concentration ratio data on fish supported the idea that Sr/Ca ratios can provide information on the environmental history of individual fish. Body concentrations of mercury were related to otolith analyses to suggest age structure, critical life history periods, growth environment, stock structure, food web position, and migration history. The techniques applied present an innovative approach to management-related problems, and the combination of chemical analyses with structural analyses promises to expand our knowledge of the life history of migratory fishes.     

Patterns of connectivity among populations of a coral reef fish

Knowledge of the patterns and scale of connectivity among populations is essential for the effective management of species, but our understanding is still poor for marine species. We used otolith microchemistry of newly settled bicolor damselfish (Stegastes partitus) in the Mesoamerican Reef System (MRS), Western Caribbean, to investigate patterns of connectivity among populations over 2 years. First, we assessed spatial and temporal variability in trace elemental concentrations from the otolith edge to make a ‘chemical map’ of potential source reef(s) in the region. Significant otolith chemical differences were detected at three spatial scales (within-atoll, between-atolls, and region-wide), such that individuals were classified to locations with moderate (52 % jackknife classification) to high (99 %) accuracy. Most sites at Turneffe Atoll, Belize showed significant temporal variability in otolith concentrations on the scale of 1–2 months. Using a maximum likelihood approach, we estimated the natal source of larvae recruiting to reefs across the MRS by comparing ‘natal’ chemical signatures from the otolith of recruits to the ‘chemical map’ of potential source reef(s). Our results indicated that populations at both Turneffe Atoll and Banco Chinchorro supply a substantial amount of individuals to their own reefs (i.e., self-recruitment) and thus emphasize that marine conservation and management in the MRS region would benefit from localized management efforts as well as international cooperation.     

基于耳石元素微化学的江苏吕泗近岸小黄鱼生境履历重建

利用电子显微探针元素分析技术,对江苏吕泗近岸海域小黄鱼矢耳石的Sr和Ca微化学特征进行了研究.结果表明: Sr含量在小黄鱼耳石的矢状面上呈非均匀分布,总体为核心部位高,其余部分明显降低.核心高Sr区域的Sr/Ca比值为(7.10±1.00),其余部分为(4.79±1.01),两者差异极显著.后者部分个体存在Sr含量更低的区域,Sr/Ca比值为(3.51±0.76).基于这些结果重建了吕泗近岸小黄鱼的生境履历： 它们在孵化及初期发育阶段生活在高盐度生境,随后的生长和发育过程则会洄游至盐度稍低的生境;部分个体的早期发育阶段还会选择利用更低盐度的生境.     

Spatio-temporal variation in the elemental compositions of otoliths of southern bluefin tuna Thunnus maccoyii in the Indian Ocean and its ecological implication

The elements Na, Mg, Mn, Ca, Sr and Ba in otoliths of southern bluefin tuna Thunnus maccoyii , collected from their feeding ground in the central Indian Ocean and spawning ground between southern Java and north-western Australia were measured by laser-ablation inductively coupled plasma mass spectrometry (LA-ICPMS) and compared among sampling locations and developmental stages. The Na, Mg and Mn to Ca concentration ratios were significantly higher at the larval stage than at the adult stage, and the ratio reached a peak at the first inflection point of the otolith, mean ± s.d. 43·3 ± 4·9 days after hatching and decreased sharply to a low level thereafter. The temporal change of the elements:Ca ratios in the first inflection point corresponded to the life stage transition from larva to juvenile, indicating that the uptake rate of elements from ambient waters was significantly influenced by the ontogenetic change in the fish. The elemental composition at the otolith edge differed significantly in sub-adults on the feeding grounds and adults on the spawning grounds. Thus, the otolith elemental composition can be used as a biological tracer to study the time of the ontogenetic shift and to reconstruct the past migratory environmental history of T. maccoyii . In addition, the elemental composition of the otolith core of the adult was similar between feeding and spawning grounds, indicating that the fish in the Indian Ocean had the same larval origin, which is consistent with the single spawning population hypothesis.     

Changes in otolith microchemistry of the Japanese eel, Anguitta japonica, during its migration from the ocean to the rivers of Taiwan

The newly recruited Japanese eel, Anguilla japonica , elvers and 1-year-old eels collected in estuaries and in rivers, respectively, were studied. The microstructure and chemical composition of the sagittal otolith of these eels were examined by SEM and wavelength-dispersive spectrometer (WDS), A transition zone or'elver mark'was observed in the otolith of the young eels. A comparison of the otoliths of elvers with those from the 1-year-old eels suggests that this transition zone was deposited during upstream migration, a change from a marine to freshwater environment. Strontium (Sr) content in the primordium of the otolith of both elvers and young eels was low, probably due to the maternal or freshwater origin of the oocyte. The concentration of Sr in the otolith increased gradually during marine life and reached a peak approximately 1 month before upstream migration. As the elvers entered the estuary, the Src concentration dramatically decreased and remained at a low level thereafter. These findings indicate that the history of the migratory environment of the eel can be reconstructed from a combined study of otolith microstructure and microchemistry analysis.