The strontium content of roe collected from spawning brown trout Salmo trutta L. reflects recent otolith microchemistry

The relationship between the strontium content of the outer layers of otoliths (an indication of recent marine, estuarine or riverine habitat use) and the strontium content of roe in ripe female brown trout Salmo trutta was examined in fish collected from the Pomahaka River and the lower reaches of the Clutha River, South Island, New Zealand. A close relationship was found between the strontium content of roe and the outer layers of otoliths. This finding suggests that spawned eggs collected from redds could potentially be used to track the extent of upstream spawning migrations by anadromous brown trout.     

Assessment of spawning site fidelity in interior Fraser River Coho salmon Oncorhynchus kisutch using otolith microchemistry,in British Columbia,Canada

Coho Salmon Oncorhynchus kisutch show fidelity to natal spawning watersheds. Fine-scale homing, however, within rivers is not well understood. Interior Fraser Coho (IFC) salmon eggs were incubated at known spawning locations in the Coldwater River, two main stem sites and one-off channel pond site, providing otolith reference data for comparison to otolith signatures for returning adults using laser ablation inductively coupled plasma mass spectrometry. Elemental ratios for Ba:Ca and Sr:Ca in otoliths of juvenile O. kisutch differed significantly among the spawning locations examined. Juvenile otolith data were used to conduct a linear discriminant analysis to assess fine-scale homing in adults. Juvenile data were all assigned to the location where they had been incubated, producing a robust data set used to compare adult otoliths and define natal locations based on elemental signatures in otoliths of adult spawners. Homing and straying were apparent at the reach level; 57.1% of adults returned to their natal spawning locations, while 42.9% strayed to other spawning sites within the Coldwater River. Straying to novel incubation sites at the reach scale demonstrated plasticity in homing within a watershed.     

Inshore migration and otolith microstructure/microchemistry of anguillid glass eels recruited to Iceland

The timing of catches of anguillid glass eels and their otolith microstructure and microchemistry were studied in southwest Iceland, where the European eel, Anguilla anguilla and American eel, A. rostrata have been thought to live sympatrically, to learn about their early life history and the possible mechanism of the separation between these two species ranges. Catches at the site studied suggest that glass eels may have started upstream migration as the river temperature warmed in late June and early July. The glass eels were mitochondrially identified into two species, A. anguilla and A. rostrata, although the latter were likely hybrids between the two species based on a different study. Otolith analyses showed no sharp increases in otolith increment width or sharp decrease of otolith Sr:Ca ratio in either species, which are the characteristic changes corresponding to the onset of metamorphosis in many anguillid species including A. rostrata collected in North America and A. anguilla in Europe. The mean age at recruitment determined for the glass eels in Iceland were similar between the two species (336.6 ± 41.7 and 319.3 ± 36.0 days for A. anguilla and A. rostrata, respectively), as were their total lengths (range 58.0–78.5 mm and 58.5–73.0 mm). In addition, mean age at metamorphosis (278.0 ± 36.8 and 254.0 ± 47.7 days) and total age (372.3 ± 50.8 and 352.9 ± 42.6 days) were also similar between the two species. However, these ages of A. rostrata in Iceland were older than those in North America, and those of A. anguilla collected in Iceland were roughly intermediate between the rest of Europe and North Africa. These findings support the hypothesis that the timing of metamorphosis is a key factor for determining the place of recruitment of glass eels and maintaining the geographic separation between the two species.     

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.     

The effect of otolith storage methods on the concentrations of elements detected by laser-ablation ICPMS

Otoliths of male (1+ year old) Terubok, tropical shad Tenualosa toli from the Lupar River, Sarawak, were treated in different ways to assess the effect of post-capture storage on element concentrations in the otolith core and edge detected by laser-ablation inductively coupled plasma mass spectrometry (ICPMS). Five treatments were compared: rapid removal and dry storage; fish kept 5 h after capture then otoliths removed; rapid removal and stored in alcohol; fish rozen for 24 h then otoliths removed; and storage of intact head in alcohol for several weeks. Seven elements were detected at the core and edge of otoliths (Li, Na, Mg, Mn, Co, Sr, Ba). Of these, Na, Mg, Co and Ba differed among treatments, being highest in treatments where the otolith remained in the head. Variation in element measurements due to treatment effects was similar to within-otolith variation for the other elements and was least variable in the fresh treatment. The variation in concentration between the core and edge was more significant than other sources of variation (up to 100 times) for some elements. These differences were probably due to physiological factors (ontogenetic) or to yearly changes in water chemistry. The results indicate that the method of otolith storage, especially freezing whole fish, can have a small, but measurable, effect on the concentrations of Na, Mg, Co and Ba.     

Seeking the true time: Exploring otolith chemistry as an age-determination tool

Fish otoliths' chronometric properties make them useful for age and growth rate estimation in fisheries management. For the Eastern Baltic Sea cod stock (Gadus morhua), unclear seasonal growth zones in otoliths have resulted in unreliable age and growth information. Here, a new age estimation method based on seasonal patterns in trace elemental otolith incorporation was tested for the first time and compared with the traditional method of visually counting growth zones, using otoliths from the Baltic and North seas. Various trace elemental ratios, linked to fish metabolic activity (higher in summer) or external environment (migration to colder, deeper habitats with higher salinity in winter), were tested for age estimation based on assessing their seasonal variations in concentration. Mg:Ca and P:Ca, both proxies for growth and metabolic activity, showed greatest seasonality and therefore have the best potential to be used as chemical clocks. Otolith image readability was significantly lower in the Baltic than in the North Sea. The chemical (novel) method had an overall greater precision and percentage agreement among readers (11.2%, 74.0%) than the visual (traditional) method (23.1%, 51.0%). Visual readers generally selected more highly contrasting zones as annuli whereas the chemical readers identified brighter regions within the first two annuli and darker zones thereafter. Visual estimates produced significantly higher, more variable ages than did the chemical ones. Based on the analyses in our study, we suggest that otolith microchemistry is a promising alternative ageing method for fish populations difficult to age, such as the Eastern Baltic cod.     

金枪鱼类耳石微化学研究进展

近年来,基于鱼类钙化物质中微量元素和同位素等微化学成分分析已成为分析鱼类种群结构、生活史及洄游环境史等的一种新兴手段.随着鱼类耳石微化学研究及应用的日渐成熟与完善,该手段也日益成为金枪鱼类生态学研究的良好工具.目前金枪鱼类耳石微化学的研究内容主要包括微量元素和同位素等,其中微量元素是应用研究的重点和热点,其在金枪鱼类,尤其是蓝鳍金枪鱼种群划分、出生源、洄游环境史和生活史分析等方面发挥了重要的作用.但多数研究集中在耳石锶钙比率(Sr/Ca)的变化上,且关于耳石碳氧同位素分馏与温度之间的关系尚无定论.为了开发耳石微化学的巨大价值,有必要加强对其沉积机理的研究,并采用综合研究方法从时空角度分析耳石中多种微量元素的含量及其变化.     

Reconstructing larval growth and habitat use in an amphidromous goby using otolith increments and microchemistry

High‐resolution analysis of growth increments, trace element chemistry and oxygen isotope ratios (δ¹⁸O) in otoliths were combined to assess larval and post‐larval habitat use and growth of Awaous stamineus, an amphidromous goby native to Hawai‘i. Otolith increment widths indicate that all individuals experience a brief period of rapid growth during early life as larvae and that the duration of this growth anomaly is negatively correlated with larval duration. A protracted high‐growth period early in larval life is associated with a lower ratio of Sr:Ca, which may reflect low salinity conditions in nearshore habitats. A distinct shift in δ¹⁸O (range: 4–5‰) is closely associated with the metamorphic mark in otoliths, indicating that larval metamorphosis occurs promptly upon return to fresh water. Strontium and other trace elements are not as tightly coupled to the metamorphosis mark, but confirm the marine‐to‐freshwater transition. Integration of microstructural and microchemical approaches reveals that larvae vary substantially in growth rate, possibly in association with habitat differences. Although time and financial costs make it difficult to achieve large sample sizes, present results show that examining even a small number of individuals can lead to novel inferences about early life history in diadromous fishes and illustrates the value of integrating analyses.     

Life history and genetic characterisation of sea trout Salmo trutta in the Adriatic Sea

1. The brown trout Salmo trutta is characterised by both anadromous (sea trout) and resident populations, naturally occurring in Atlantic and Ponto-Caspian rivers. Sea trout are currently considered absent from rivers of the Mediterranean area, probably because of the non-optimal chemical–physical characteristics of the Mediterranean Sea. However, the occasional bycatch of smoltified S. trutta in the Adriatic Sea is well known among fishermen and the biological explanation of this phenomenon is still controversial. The aim of this study was to compare the genetic diversity of freshwater and marine brown trout to try to understand the factors underlying the presence of putative anadromous brown trout in the Adriatic Sea.
2. In this study, we analysed the genetic diversity of: (1) wild brown trout collected from the Esino River (central Italy); (2) a domestic strain of brown trout used for stocking the study area; and (3) a sample of Adriatic sea trout collected near the outlet of the Esino River. Together with genetic analysis, we carried out scale analysis in order to track the freshwater/marine stages of the life cycle in the sea trout samples. The genetic characterisation was carried out by polymerase chain reaction–restriction fragment length polymorphism analysis of the mtDNA fragment ND-5/6 and the nuclear locus LDH-C1* and by genotyping 15 microsatellite loci. The genetic polymorphism obtained was used to investigate intra- and inter-population genetic diversity, rates of genetic introgression between wild and domestic samples and the origin of sea trout specimens by using assignment tests.
3. Our genetic analyses demonstrated that the sea trout analysed in this study are from the domestic strain of Atlantic origin used in central Italy for stocking activities. The level of genetic introgression between native and domestic samples is high in the Esino River. The populations more resilient to introgressive hybridisation appeared to be those living in the portion of the river network dominated by carbonate rocks. Assignment tests (GeneClass) suggest the existence of a link between stocking efforts and the freshwater origin of the sea trout. In addition, data obtained from the analysis of scales, size measurement, and sex determination showed a pattern of smolt age, size, and sex ratio very similar to those observed in other anadromous populations.
4. In conclusion, the present study highlighted that sea trout from the central Adriatic Sea originated from brown trout of Atlantic origin inhabiting the Esino River. Their seaward migratory behaviour could represent a consequence of an active migration instead of a passive displacement by water flow. Our results also showed that traditional stocking practices represent a negative activity for the conservation of the last Mediterranean native S. trutta populations.

     

Flexible migration of Japanese freshwater gobies Rhinogobius spp. as revealed by otolith Sr:Ca ratios

The migratory histories of six Rhinogobius spp., the cross‐band type (R. sp. CB), the large‐dark type (R. sp. LD), the dark type (R. sp. DA), the cobalt type (R. sp. CO), the orange type (R. sp. OR) and R. flumineus, were studied by examining strontium (Sr) and calcium (Ca) concentrations in their otoliths using wavelength dispersive X‐ray spectrometry on an electron microprobe. The Sr:Ca ratios in the otoliths changed both with the ontogenetic development and with the salinity level of the habitat. Most fishes had high Sr:Ca ratios around the otolith core in spite of the fact that those fishes live most of their lives in a freshwater environment. The high ratios in the otoliths were thought to be a physiological effect in those fishes. Thereafter, the Sr:Ca ratios changed remarkably along the life‐history transect, showing intraspecies and interspecies variations. The otolith Sr:Ca ratios of Rhinogobius sp. CB, R. sp. LD and R. sp. CO collected from three rivers connected to the sea were low around the core, subsequently increased sharply to the points 180–345 μm from the core and then decreased again towards the edge. They were thought to reflect the typical amphidromous life history. The R. sp. CO, however, remain in a brackish‐water environment after migration from the sea, while the other species showed typical amphidromous lives with complete freshwater residence after migration from the sea. The five species (R. sp. CB, R. sp. LD, R. sp. CO, R. sp. DA and R. sp. OR) collected above dams had never migrated to the sea, spending their whole life in a freshwater environment, although Rhinogobius species, except for the fluvial type, were thought to have an amphidromous life history according to previous studies. These species are thought to have a landlocked life cycle. The otolith Sr:Ca ratios of R. flumineus showed consistently low ratios towards the edge except for only around the core, although they were collected from a river connected to the sea. These species could have a fluvial life history corresponding to a previous study. The present study clearly suggests that the migratory histories of Rhinogobius spp. are highly different both within and between species and that they have flexible migratory patterns allowing them to utilize the full range of salinity during their life history.     

Effects of ethanol preservation on otolith microchemistry

Solution‐based inductively coupled plasma‐mass spectrometry was used to examine the effects of exposure time to ethanol (0, 1, 3, 9, 27 and 81 days) and ethanol quality (ACS‐ v . HPLC‐grade) on strontium (Sr) and barium (Ba) concentrations in sagittal otoliths of hatchery‐raised and wild‐caught young‐of‐the‐year walleye Stizostedion vitreum . No effect of either attribute on Sr and Ba concentrations were detected, indicating that metabolically inert elements that replace calcium in the calcium carbonate matrix ( e.g . Sr and Ba) are not influenced by storage in 95% ethanol.     

Assessing the role of ontogenetic movement in maintaining population structure in fish using otolith microchemistry

Identifying the mechanisms maintaining population structure in marine fish species with more than a single dispersing life stage is challenging because of the difficulty in tracking all life stages. Here, a two‐stage otolith microchemistry approach to examining life‐stage movement was adopted, tracking a year‐class from the juvenile to adult stage and inferring larval sources from clustering, in order to consider the mechanisms maintaining population structuring in North Sea cod. Clustering of near‐core chemistry identified four clusters, two of which had either a southern or northern affinity and were similar to juvenile edge chemistry. The other two clusters, common to the central North Sea, had intermediate chemical composition and may have reflected either larval mixing in this region or a lack of geographic heterogeneity in the elemental signature. From the comparison of whole juvenile and the corresponding component of adult otoliths, adults from the southern North Sea mostly recruited from adjacent nursery grounds. In contrast, many adults in the northern North Sea had a juvenile chemistry consistent with the Skagerrak and juveniles from the northern Skagerrak site had a near‐core chemistry consistent with the northern North Sea. Similarities in otolith chemistry were consistent with retention of early life stages at a regional level and also juvenile and adult fidelity. The links between the northern North Sea and Skagerrak indicate natal homing, which when considered in the context of genetic evidence is suggestive of philopatry. The approach used here should be useful in exploring the mechanisms underlying population structuring in other species with multiple dispersive life stages and calcified hard parts.     

Interspecific variations of otolith chemistry in estuarine fish nurseries

Otolith chemical composition differed between juveniles of five fish species ( Solea solea , Solea senegalensis , Platichthys flesus , Diplodus vulgaris and Dicentrarchus labrax ) in nursery areas of six estuaries along the Portuguese coast (Douro, Ria de Aveiro, Mondego, Tejo, Sado and Mira). Spatially consistent patterns in the concentration of some elements were responsible for differences between species. Discrimination of estuaries using data from all species simultaneously averaged 44·7% of correctly classified cases, whilst discrimination of species averaged 76·2%. Moreover, species-related patterns in otolith fingerprints were highlighted when comparing species for each estuarine nursery area, with intra estuarine species discrimination averages ranging from 86·2 to 100·0%. Similarities in the otolith elemental fingerprints were larger between species with close phylogeny and ecology, particularly between flatfish and perciform species. In addition to the differences in physiological regulation of species, specific microhabitat use in a common environment was suggested as a relevant factor for the differentiation of otolith chemistry among species occurring in the same locations. Despite positive results in specific estuaries, variation in otolith composition limited the use of species as proxies to classify others to their system of origin.     

Use of otolith chemistry to examine patterns of diadromy in the threatened Australian grayling Prototroctes maraena

Otolith chemical analyses (proton-induced X-ray emission and laser ablation inductively coupled plasma mass spectrometry) were used to examine patterns of diadromy in Australian grayling Prototroctes maraena collected from three rivers in south-eastern Australia. Concentrations of Sr:Ca and Ba:Ca were measured in the sagittal otoliths of 25 fish and in water samples collected on two occasions from multiple sites within freshwater, estuarine and marine reaches of the rivers. The results provide evidence of marine residency during the juvenile phase, with high Sr:Ca and low Ba:Ca in the inner region of the otoliths that were consistent across all three rivers. This general pattern was apparent for all individuals examined, suggesting that diadromous migration may be an obligate aspect of the life history. The chemical signatures of the outer regions of the otoliths were distinct between the three rivers, whilst there was no difference in the inner regions of the otoliths. This suggests that juveniles from different rivers may reside in a relatively homogenous chemical environment, such as the sea, and populations in coastal Victorian rivers may share a common marine recruitment source.     

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。     

Discrimination of French grunts (Haemulon flavolineatum, Desmarest, 1823) from mangrove and coral reef habitats using otolith microchemistry

Using French Grunts (Haemulon flavolineatum) held captive within mangrove and reef sites, we determined (a) whether otolith microchemical differences existed between mangroves and reefs separated at a biologically relevant spatial scale (0.25-7.1 km), (b) whether patterns in elemental concentrations were consistent across years, and (c) whether it was possible to identify whether a given fish occupied a mangrove as a juvenile.Three sites were established at Great Exuma, Bahamas (two reefs and one mangrove, May 2001) and at Turneffe Atoll, Belize (one reef and two mangroves, August 2001 and 2002). Using concentrations of Sr and Ba, discriminant function analysis (DFA) indicated unique spatial microchemical signatures of fish from each of the three Bahamas sites allowing an average correct classification of 77%. Using concentrations of Sr, Ba, Sn and Pb (2001), and in addition Li, Mg, Cu and Rb (2002), DFA of the three Belize sites indicated an average correct classification of 68% and 85% in 2001 and 2002, respectively. To assess temporal variability in otolith microchemistry, we compared microchemical signatures of Belize fish from 2001 to those from 2002. On average, 42% of fish from 2002 were correctly classified to their captive sites using chemical information from 2001, thus suggesting considerable temporal variability in otolith microchemistry. Finally, to identify whether a given fish occupied a mangrove during its juvenile stage, we ablated the juvenile portion of the otolith taken from reefs in Belize 2002. Results of this analysis indicated that 36% of 39 individuals taken from the reef had a signature more representative of one of the mangrove sites. Although otolith microchemistry varied temporally and our analysis was restricted to the grouping of individuals to only one of three sites, mangroves appeared to contribute to reef populations.     

Onset of maturity and cohort composition at spawning of Baltic sprat Sprattus sprattus on the basis of otolith macrostructure analysis

Data on catch per unit effort (CPUE) from the Danish commercial fishery showed dense aggregations of sprat Sprattus sprattus born in 1997 in the main spawning area of the Baltic Sea during May 1999. After the analysis of their otolith macrostructure, these fish were found to have a shorter distance to the beginning of the first winter zone compared to fish from the same cohort caught in other months. At the same time, the number of fish with large otoliths at the period of winter zone formation tended to decrease or even disappear. The otolith size at winter zone formation ( O _W) was found to be a good predictor of sprat total length ( L _T) and mass ( M ) in age group 0 years. Changes in the otolith size distribution over time were related to variations in cohort composition depending on the L _T and M attained during the juvenile stage. Examination of the gonads suggested two life history patterns: 1) individuals achieving a larger L _T and M during the first growing season may contribute at age 1 years to the spawning stock and the fishery, whereas 2) individuals attaining smaller L _T and M contribute in larger amounts to both the spawning stock and the fishery later, when they are at age 2 years. Moreover, changes in the relationship between O _W and L _T and M were related to differences in growth trajectories for sprat born during the same spawning season. Smaller sprat as group 0 years continued growing during the second growing season delaying maturity compared to larger individuals from the same cohort.     

Migratory patterns and contribution of stocking to the population of European eel in Lithuanian waters as indicated by otolith Sr:Ca ratios

Otolith Sr:Ca ratios were examined to evaluate the contribution of the stocked eel Anguilla anguilla elvers, which have been stocked in Lithuanian waters and mixed with naturally recruited eels for several decades, to the native eel population. Stocked eels were identified by the freshwater signature (Sr:Ca ratios <2·24 × 10⁻³) on the otolith after the glass eel stage. Naturally recruited eels, that had migrated through the North and Baltic Seas, were characterized by an extended seawater and brackish-water signature (Sr:Ca ratios >3·23 × 10⁻³) after the glass eel stage. Of 108 eels analysed, 21 eels had otolith Sr:Ca ratio profiles consistent with stocking while 87 showed patterns of natural recruitment. The ages of naturally recruited eels arriving in Lithuanian fresh waters varied from 1 to 10 years, with a mean ±  s.d . age of 5·2 ± 2·1 years. Eels from the inland Lake Baluošai were all freshwater residents of stocked origin. Stocked eels, however, accounted for only 20% of the eels from the Curonian Lagoon and 2% of eels sampled in Baltic coastal waters. This finding does not support the hypothesis that the eel fishery in the Curonian Lagoon depends mostly on stocking.