Incorporation of strontium into otoliths of an estuarine fish

Patterns of Sr/Ca variability in fish otoliths have been widely applied as tracers of movement between freshwater and marine habitats, with the assumption that low salinity habitats correspond to lower otolith levels of Sr/Ca. On the other hand, fluvial estuaries can contain steep gradients in Sr/Ca, and in some estuaries, freshwater values of Sr/Ca can exceed marine values, which are relatively constant across marine habitats. Therefore, to interpret Sr/Ca variability in otoliths of fish that move through estuaries, information is needed about both the incorporation of strontium into otoliths and the nature of the gradient of Sr/Ca in the water. We conducted four experiments to evaluate the incorporation of strontium into fish otoliths under estuarine conditions, using white perch (Morone americana) as a model estuarine fish. One laboratory and the two field experiments tested the relationship between Sr/Ca in the otolith and that in the water. A fourth experiment investigated the effect of salinity, independently of the water chemistry (Sr was manipulated while maintaining a constant salinity and Ca level). All four experiments supported a direct relationship between Sr/Ca in the otolith and the water, across a range of estuarine salinities. Results also indicated that the incorporation of strontium into otoliths of estuarine fishes should be constant across broad gradients of Sr/Ca in estuarine waters. While the experiments supported past applications of tracing estuarine and diadromous movements with otolith Sr/Ca chronologies, we emphasize the need to understand the underlying nature of Sr/Ca gradients in estuaries, which may limit or confound reconstructions of estuarine habitat use.     

Extrinsic factors affecting otolith chemistry – implications for interpreting migration patterns in a diadromous fish

Much has been revealed about fish migration, including diadromous behaviour, through the use of otolith chemistry. Manipulative experiments assist with unravelling information on otolith chemical composition and incorporation thereby answering specific questions on diadromous movements. In this study, a laboratory-based experiment was used to determine the relative and interactive effects of salinity and water temperature on the composition of three key elements (Sr, Ba and Mg) within the otolith of a catadromous fish, Percalates novemaculeata, endemic to south-eastern Australia. Otolith incorporation of Sr and Ba was positively related to ambient water concentration, whereas Mg incorporation was not. Sr and Ba increased and decreased significantly across salinity gradients, respectively, with minor positive effects of temperature also being detected. Salinity and temperature interacted to significantly affect the elemental concentration ratios for Ba: Ca in otoliths. Discrimination between fresh water and marine environments shows promise for interpreting P. novemaculeata residency based on these elements alone. However, deciphering finer scale movements within estuarine environments may be difficult. Our data highlights the importance of multifactorial validation experiments and suggests complementary use of multiple approaches for unravelling species-specific patterns of fish movement and habitat use.     

Microprobe analyses of anadromous Arctic charr, Salvelinus alpinus, otoliths to infer life history migration events

Otoliths of Arctic charr, Salvelinus alpinus, from north Labrador were examined to gather life history information pertinent to anadromous migrations. Wavelength dispersive electron microprobe measurements confirm the presence of strontium in otolith tissue. Trace element analyses of charr otoliths imply that otolith strontium/calcium concentration ratios are related to external environmental factors with salinity having a great influence. Otoliths clearly record habitat shifts consistent with migration across major salinity boundaries. Most charr first migrate to sea following at least 2 years in freshwater. Generally, when anadromy begins, it continues annually. Robust relationships in otolith chemistry, combined with macrostructure patterns in field-captured specimens, provide time-series data describing individual migrational histories. Validation studies are still required in order to couple information contained within daily increments with chemical analyses to infer additional temporal events in diadromous migrations. Received: 6 November 1996 / Accepted: 18 May 1997     

Fish otolith chemistry influenced by exposure to multiple environmental variables

There is an increasing desire for researchers to use the elemental concentrations in fish otoliths to reconstruct environmental histories of fish. These reconstructions may be plausible due to the unique incorporation of elements into discrete layers of otolith material that correspond to daily growth, and because environmental variables of temperature, salinity, and water chemistry can influence otolith chemistry. However, it is essential to establish exactly how temperature, salinity, and the ambient concentration of elements influence otolith chemistry in order to interpret environmental histories of fish. Using a controlled laboratory experiment we tested the relative and interactive effects of temperature, salinity, and ambient concentration of strontium (Sr) and barium (Ba) on the resulting concentration of Sr and Ba in otoliths of black bream Acanthopagrus butcheri (Munro 1949). Salinity and concentration, and temperature and concentration interacted to affect the elemental concentration of Sr:Ca and Ba:Ca in otoliths. Regression analysis revealed that temperature and ambient concentration contributed most to the trend in otolith chemistry for both elements. Importantly, this is the first experiment to combine three environmental variables and assess their effect on otolith chemistry. Based on these results, it should be possible to use changes in the elemental concentration in otoliths to better reconstruct previous environments of temperature, salinity, and ambient water chemistry, which is especially useful when determining occupancy in habitats such as estuaries that display variable environmental characteristics.     

Contribution of water chemistry and fish condition to otolith chemistry: comparisons across salinity environments

This study quantified the per cent contribution of water chemistry to otolith chemistry using enriched stable isotopes of strontium (⁸⁶Sr) and barium (¹³⁷Ba). Euryhaline barramundi Lates calcarifer, were reared in marine (salinity 40), estuarine (salinity 20) and freshwater (salinity 0) under different temperature treatments. To calculate the contribution of water to Sr and Ba in otoliths, enriched isotopes in the tank water and otoliths were quantified and fitted to isotope mixing models. Fulton's K and RNA:DNA were also measured to explore the influence of fish condition on sources of element uptake. Water was the predominant source of otolith Sr (between 65 and 99%) and Ba (between 64 and 89%) in all treatments, but contributions varied with temperature (for Ba), or interactively with temperature and salinity (for Sr). Fish condition indices were affected independently by the experimental rearing conditions, as RNA:DNA differed significantly among salinity treatments and Fulton's K was significantly different between temperature treatments. Regression analyses did not detect relations between fish condition and per cent contribution values. General linear models indicated that contributions from water chemistry to otolith chemistry were primarily influenced by temperature and secondly by fish condition, with a relatively minor influence of salinity. These results further the understanding of factors that affect otolith element uptake, highlighting the necessity to consider the influence of environment and fish condition when interpreting otolith element data to reconstruct the environmental histories of fish.     

Preliminary investigation on otolith microchemistry of naked carp (Gymnocypris przewalskii) in Lake Qinghai, China

The paper represents the first otolith study on trace element (Sr, Mg) concentrations of naked carp (Gymnocypris przewalskii), an endemic and endangered migratory species in high-altitude Lake Qinghai and its tributaries of China, using electron probe microanalysis (EPMA). Results from life-history transect analyses and X-ray intensity maps suggested that the general reference criterion for discrimination of the salinity habitats of freshwater, brackish and seawater by the otolith Sr:Ca ratio of diadromous fish cannot be used as a reliable indicator for reconstructing the migration history of naked carp between different habitats. On the contrary, Mg concentrations and Mg:Ca ratios were found inconsistent in all otolith samples of G. przewalskii. The otolith regions with higher Mg concentrations (greenish) might coincide with the period that yolk provides nutrition to G. przewalskii. The lower Mg:Ca ratios in most regions of otolith showed that Mg in G. przewalskii might be regulated to that low level during its lifespan in Lake Qinghai. This suggests that the distinct EPMA approach can provide new visualization insight into the ontogenetic and migration patterns of G. przewalskii.     

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。     

Freshwater habitat use by a moray eel species,Gymnothorax polyuranodon,in Fiji shown by otolith microchemistry

Freshwater eels of the Anguillidae are diadromous because they migrate between ocean and freshwater environments, but other anguilliform fishes are generally considered to be strictly marine species. A few marine eels of the Muraenidae and Ophichthidae have occasionally been found in freshwater or estuaries, indicating that anguillids are not the only anguilliform eels that can use freshwater in some parts of the world. The moray eel Gymnothorax polyuranodon is one species that is known to be present in freshwater in the Indo-Pacific, but its life history is unknown. One way to evaluate what types of habitats are used by fishes is to determine the ratio of strontium (Sr) to calcium (Ca) in their otoliths, because this can show if they have used freshwater or saltwater environments. To evaluate the patterns of freshwater use by this unusual species of marine eel, the otolith Sr/Ca ratios of four G. polyuranodon (275–344 mm) caught in a freshwater stream of Fiji were analyzed. The consistently low Sr/Ca values (0–4) indicated upstream movement after settlement and freshwater or estuarine residence of all four individuals. These eels did not appear to have entered freshwater just for a short time period, which is consistent with other reports that this species is present in estuarine and freshwater habitats. This suggests that G. polyuranodon may be a catadromous species of marine eel. The similarities and differences between the life histories of anguillid eels and the few marine eels that have evolved the ability to invade freshwater habitats is discussed in relation to the evolutionary origin of diadromy in anguilliform fishes that originated in the marine environment.     

Movements of diadromous fish in large unregulated tropical rivers inferred from geochemical tracers

Patterns of migration and habitat use in diadromous fishes can be highly variable among individuals. Most investigations into diadromous movement patterns have been restricted to populations in regulated rivers, and little information exists for those in unregulated catchments. We quantified movements of migratory barramundi Lates calcarifer (Bloch) in two large unregulated rivers in northern Australia using both elemental (Sr/Ba) and isotope ((87)Sr/(86)Sr) ratios in aragonitic ear stones, or otoliths. Chemical life history profiles indicated significant individual variation in habitat use, particularly among chemically distinct freshwater habitats within a catchment. A global zoning algorithm was used to quantify distinct changes in chemical signatures across profiles. This algorithm identified between 2 and 6 distinct chemical habitats in individual profiles, indicating variable movement among habitats. Profiles of (87)Sr/(86)Sr ratios were notably distinct among individuals, with highly radiogenic values recorded in some otoliths. This variation suggested that fish made full use of habitats across the entire catchment basin. Our results show that unrestricted movement among freshwater habitats is an important component of diadromous life histories for populations in unregulated systems.     

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.     

Flexible Life History Strategies of Ninespine Sticklebacks,Genus <Emphasis Type="BoldItalic">Pungitius</Emphasis>

Synopsis We studied the life histories of the ninespine sticklebacks, Pungitius pungitius and Pungitius tymensis, collected from Japanese freshwater and brackish (sea) water habitats by examining the strontium (Sr) and calcium (Ca) concentrations in their otoliths. The Sr:Ca ratios in the otoliths changed with the salinity of the habitat regardless of identification as freshwater or brackish water type based on morphological characteristics. The ninespine sticklebacks living in a freshwater environment showed consistently low Sr:Ca ratios throughout the otolith. These samples were identified as a standard freshwater type. In contrast, all freshwater-type fishes collected from the intertidal zone showed higher otolith Sr:Ca ratios than those in the standard freshwater type, and the ratios fluctuated with the growth phase. All brackish water-type fishes collected in the intertidal zone showed the highest otolith Sr:Ca ratio throughout the otolith. In the present study, besides the two representative life history types of P. pungitius, i.e., freshwater and brackish water life history types, other sticklebacks had an anadromous life history type. These findings clearly indicate that the ninespine stickleback has a flexible migration strategy with a high degree of behavioral plasticity and an ability to utilize the full range of salinity in its life history.     

Migration flexibility between freshwater and marine habitats of the pond smelt Hypomesus nipponensis

The life histories of the pond smelt Hypomesus nipponensis collected from Japanese fresh waters and brackish (sea) waters were studied by examining the strontium (Sr) and calcium (Ca) concentrations in their otoliths. The Sr:Ca ratios in the otoliths changed with the salinity of the habitat. The pond smelt living in a freshwater environment showed consistently low Sr:Ca ratios throughout the otolith, averaging 1·2–1·3 × 10⁻³. These samples were identified as a standard freshwater type. In contrast, fish collected from the intertidal zone showed higher otolith Sr:Ca ratios than those in the standard freshwater type, and the ratios fluctuated along the growth phase. In addition to the two representative life‐history types of H. nipponensis , i. e . freshwater and anadromous life‐history types, other pond smelts were found to have an estuarine resident life history‐type with no freshwater phase, indicating that the pond smelt has a flexible migration strategy with a high degree of behavioural plasticity and an ability to utilize the full range of salinity in its life history.     

Low interbasin connectivity in a facultatively diadromous fish: evidence from genetics and otolith chemistry

Southern smelts (Retropinna spp.) in coastal rivers of Australia are facultatively diadromous, with populations potentially containing individuals with diadromous or wholly freshwater life histories. The presence of diadromous individuals is expected to reduce genetic structuring between river basins due to larval dispersal via the sea. We use otolith chemistry to distinguish between diadromous and nondiadromous life histories and population genetics to examine interbasin connectivity resulting from diadromy. Otolith strontium isotope (⁸⁷Sr:⁸⁶Sr) transects identified three main life history patterns: amphidromy, freshwater residency and estuarine/marine residency. Despite the potential for interbasin connectivity via larval mixing in the marine environment, we found unprecedented levels of genetic structure for an amphidromous species. Strong hierarchical structure along putative taxonomic boundaries was detected, along with highly structured populations within groups using microsatellites (F_ST = 0.046–0.181), and mtDNA (Φ_ST = 0.498–0.816). The presence of strong genetic subdivision, despite the fact that many individuals reside in saline water during their early life history, appears incongruous. However, analysis of multielemental signatures in the otolith cores of diadromous fish revealed strong discrimination between river basins, suggesting that diadromous fish spend their early lives within chemically distinct estuaries rather than the more homogenous marine environment, thus avoiding dispersal and maintaining genetic structure.     

Consistency of elemental and isotope‐ratio patterns across multiple scales from individual fish

Assays of elemental and stable‐isotope ratios across growth increments of scales have the potential to provide a non‐lethal alternative to otolith chemistry for identifying migration and ontogenetic trophic shifts. A central assumption when employing scales as otolith analogues is that any scale from an individual will provide equivalent information about the chemical history of that fish. This assumption was investigated with multiple scales from wild and captive euryhaline Atlantic tarpon Megalops atlanticus from the north‐west Gulf of Mexico. Elemental (Sr:Ca) and isotope‐ratio (δ¹³C and δ¹⁵N) life‐history profiles were compared among multiple scales from each fish. All three chemical proxies showed highly consistent patterns among non‐regenerated scales, while patterns in regenerated scales diverged, indicating rapid regrowth of interior scale material at the onset of regeneration. Patterns of Sr:Ca and δ¹³C covaried, supporting their use as salinity proxies, while δ¹⁵N patterns were consistent with ontogenetic diet shifts. Water samples taken from aquaria holding captive fish were used to calculate partition coefficients for a suite of elements in M. atlanticus scales for future quantification of migratory movements in the region. Together, these results support the assumption that non‐regenerated scales from individual M. atlanticus provide equivalent chemical histories, further validating their use as a viable non‐lethal alternative to otoliths.     

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.     

Environmental signature in the otolith elemental fingerprint of the tapertail anchovy, Coilia mystus, from the Changjiang estuary, China

The ontogenetic patterns of habitat use and the migratory history of the tapertail anchovy, Coilia mystus, collected in the Changjiang estuary around Chongming Island, China, were studied by examining the environmental signature in the otolith strontium (Sr) and calcium (Ca) fingerprints using electron probe microanalysis (EPMA). Our results suggest that the migration strategy of C. mystus is much more flexible than supposed in the literature to date. The spring spawning population of C. mystus from the studied area was found to consist of individuals with different migration histories. Although the tapertail anchovy seems to be an anadromous fish that spawns and hatches in a freshwater habitat, it can also use a freshwater environment in non‐spawning seasons. The otolith EPMA of the elemental fingerprint (Sr x‐ray maps and Sr : Ca ratios) is an environmental indicator that can be applied to the migratory ecology of other important diadromous species in China.     

Otolith Sr:Ca and Ba:Ca may give inconsistent indications of estuarine habitat use for American eels (<Emphasis Type="Italic">Anguilla rostrata</Emphasis>)

Temporal patterns in otolith Sr:Ca and Ba:Ca ratio values of American eels Anguilla rostrata from two sites in western Newfoundland gave insight into the use of freshwater and saline habitats. Mean Sr:Ca and Ba:Ca values at the core zone did not differ between sites, indicative of a common oceanic origin. At the otolith edge, representing continental life, both Sr:Ca and Ba:Ca values varied between sites consistent with ambient element:Ca ratio values and salinity, with typically higher Sr:Ca and lower Ba:Ca values in saline than in fresh waters. Most eels (73%) from Muddy Hole, an estuarine site, were evaluated as estuarine residents while most (70%) eels from Castors River, a freshwater site, were evaluated as freshwater residents, with the remaining eels from each site evaluated as inter-habitat migrants. An otolith element:Ca critical value appropriate for distinguishing between fresh and saline water residence is fundamental for estimating the proportion of eel residence in freshwater and their subsequent classification into habitat residence groups. Such classification is moderately robust to the critical value selected. For inter-habitat migrants, moderate otolith Sr:Ca values between the elver check and otolith edge suggestive of estuarine residence may coincide with Ba:Ca values suggestive of freshwater residence. No general critical value for separating fresh and estuarine habitats was found for otolith Ba:Ca. Otolith Ba:Ca temporal patterns may assist the use of Sr:Ca in the evaluation of historical habitat residence and inter-habitat movement but the use of otolith Ba:Ca values should be applied cautiously for American eels and perhaps of other estuarine/freshwater migratory fishes.     

Differences in the Trace Element Deposition in Otoliths Between Marine- and Freshwater-resident Japanese Eels, Anguilla japonica, as Determined by Laser Ablation ICPMS

Synopsis In order to determine whether the trace element composition in otolith of the Japanese eel Anguilla japonica could be used to determine its habitat use, we used laser ablation inductivity coupled plasma mass spectrometry (LA-ICPMS) to assay sectioned otoliths of both marine-resident (sea eels) and freshwater-resident (river eels) eels. A close linear relationship in the Sr:Ca ratios between EPMA (X-ray analysis with an electron microprobe) and LA-ICPMS analyses was found, suggesting that the latter technique could be used to separate the marine and freshwater life phases. Elemental signatures in the otolith outside the elver mark showed significant differences in Cr:Ca, Mn:Ca, and Ba:Ca ratios as well as Sr:Ca ratios between sea and river eels. These results indicate that the elemental compositions may reflect environmental variability between marine and fresh water masses. Thus, those elemental ratios determined by LA-ICPMS analysis seem to have the potential to help distinguish the habitat of the eel.     

Salinities, not diets, affect strontium/calcium ratios in otoliths of Anguilla japonica

Although otolith Strontium (Sr)/calcium (Ca) ratios have been widely used to reconstruct the past salinity environmental history of anguillid eels, factors affecting the Sr/Ca ratios in otoliths are incompletely understood. Japanese Eel (Anguilla japonica) elvers (mean length 54.7 ± 2.1 mm) were collected in the estuary during their upstream migration and reared at 5 different salinities (0, 5, 15, 25, and 35 psu) and 3 types of feeding conditions (formulated feed, tubifex, and starvation) for 30 days to evaluate the effects of salinity and diets on otolith Sr/Ca ratios. Ca and Sr concentrations in the ambient water significantly increased with salinity (SAL) as [Ca] _water = 15.50SAL − 5.56, and [Sr] _water = 0.21SAL + 0.03, respectively. Sr/Ca ratios in otoliths increased with salinity (SAL) of the rearing water as [(Sr/Ca) × 1000] _otolith = 0.091SAL + 3.790. In diets, Sr/Ca ratios were 4 times higher in tubifex than in formulated feed. However, in otoliths, ANOVA indicated that Sr/Ca ratios did not differ significantly between groups fed on tubifex or formulated feed (p = 0.118). Otolith Sr/Ca ratios were negatively correlated with fish growth rates while the growth rates differed significantly among rearing conditions with different salinities and diets. Partition coefficients of the Sr/Ca ratios from ambient water to fish tissues and otoliths significantly increased with salinity. The Sr/Ca ratios of Japanese Eel otoliths thus were positively correlated with the ambient salinity and decreased with increasing fish growth rate, but was not affected by fish diet.     

Diverse migratory histories of Japanese Trachidermus and Cottus species (Cottidae) as inferred from otolith microchemistry

The migratory histories of Japanese freshwater sculpins, one Trachidermus and four Cottus species, 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 with salinity of the habitat. The otoliths of Cottus nozawae showed consistently low Sr : Ca ratios, with an average of 3·37 × 10^?3 from the core to the edge, suggesting a freshwater resident life cycle. In contrast, the otolith Sr : Ca ratios for Trachidermus fasciatus and Cottus kazika changed along the life history transects possibly in accordance with their migration patterns from sea to fresh water. The ratios of T. fasciatus and C. kazika averaged 5·4 × 10^?3 and 5·3 × 10^?3 respectively, in the otolith region from the core to the points 450–890 μm, and changed to the lower levels, averaging 2·0 × 10^?3 and 2·7 × 10^?3, in the outer otolith region. These data suggest that both the species have a catadromous life cycle. The otoliths of Cottus hangiongensis had low Sr : Ca ratios in the two regions from the core to the points 15–30 μm and the points 415–582 μm to the edge, averaging 2·0 × 10^?3 and 1·9 × 10^?3, with significantly higher ratios in the narrow area between these regions, averaging 4·6 × 10^?3. Similar ontogenetic changes in otolith Sr : Ca ratios were found in the otoliths of Cottus amblystomopsis, suggesting their amphidromous life cycle. These findings suggest that otolith Sr : Ca ratios reflect individual life histories and that Japanese Trachidermus and Cottus species have diverse migratory histories.