Cod otoliths document accelerating climate impacts in the Baltic Sea.

Anthropogenic deoxygenation of the Baltic Sea caused major declines in demersal and benthic habitat quality with consequent impacts on biodiversity and ecosystem services. Using Baltic cod otolith chemical proxies of hypoxia, salinity, and fish metabolic status and growth, we tracked changes from baseline conditions in the late Neolithic (4500 BP) and early twentieth century to the present, in order to understand how recent, accelerating climate change has affected this key species. Otolith hypoxia proxies (Mn:Mg) increased with expanding anoxic water volumes, but decreased with increasing salinity indexed by otolith Sr:Ca. Metabolic status proxied by otolith Mg:Ca and reconstructed growth were positively related to dissolved oxygen percent saturation, with particularly severe declines since 2010. This long-term record of otolith indicators provides further evidence of a profound state change in oxygen for the worse, in one of the world's largest inland seas. Spreading hypoxia due to climate warming will likely impair fish populations globally and evidence can be tracked with otolith chemical biomarkers.

Water temperature affects somatic growth, body condition and oxygen and carbon otolith isotopes of stout whiting (Sillago robusta).

Ocean warming will continue to affect the growth, body condition and geographic distributions of marine fishes and understanding these effects is an urgent challenge for fisheries research and management. Determining how temperature is recorded in fish otolith carbonate, provides an additional chronological tool to investigate thermal histories, preferences and patterns of movement throughout an individual's life history. The influence of three water temperature treatments (22°C, 25°C, and 28°C) on hatchery-reared juvenile stout whiting, Sillago robusta, was tested using a controlled outdoor mesocosm system. Fish were measured for change in length and weight, and body condition was determined using bioelectrical impedance analysis. Sagittal otoliths were analysed for stable oxygen (δ18Ootolith) and carbon (δ13Cotolith) isotopes via isotope ratio mass spectrometry. Whiting kept at 22°C were significantly smaller and had diminished body condition compared to fish in 25°C and 28°C, which did not significantly differ from each other. The δ18O otolith values of stout whiting demonstrated a negative temperature-dependent fractionation relationship which was similar in slope but had a different intercept to the relationships reported for inorganic aragonite and other marine fish species. The δ13C otolith values also showed a negative relationship with water temperature, and the calculated proportion of metabolic carbon M in otoliths differed between fish reared in the coolest (22°C) and warmest (28°C) temperature treatments. Overall, the results suggest that stout whiting may have reached an upper growth threshold between 25°C and 28°C, and that growth and body condition may be optimised during warmer seasons and toward the northerly regions of their distribution. Otolith oxygen thermometry shows promise as a natural tracer of thermal life history, and species-specific fractionation equations should be utilised when possible to prevent errors in temperature reconstructions of wild-caught fish.

Otolithic functions in patients with residual dizziness after successful repositioning manoeuvres for unilateral posterior canal BPPV.

OBJECTIVE: To evaluate otolithic functions in patients with residual dizziness after successful canalith repositioning procedures (CRPs) for unilateral posterior canal benign paroxysmal positional vertigo (BPPV), and to investigate possible risk factors. METHODS: This case-control observational study included healthy controls and patients with residual dizziness after improvement following CRP for BPPV. All participants were subjected to full history taking, otoscopy, audiological basic evaluation, Dix-Hallpike test to search for posterior canal BPPV, residual dizziness screening, and vestibular evoked myogenic potential (VEMP) testing. Between-group differences were assessed and possible factors associated with residual dizziness were identified by univariate analysis. RESULTS: A total of 50 patients with residual dizziness (mean age, 56.53 ± 7.46 years [29 female: 21 male]) and 50 healthy controls (mean age, 58.13 ± 7.57 years [20 female: 30 male]) were included. A significant difference in VEMP latencies was found between the patient and control group (delayed in the patient group), with no significant between-group difference in amplitude in both ears. Aging, female sex, long duration of BPPV, number of CRPs, cervical VEMP and ocular VEMP abnormalities, and winter onset, were significantly associated with the risk of residual dizziness. CONCLUSIONS: Residual dizziness is a frequent sequel of BPPV that may relate to otolithic dysfunction. VEMP changes were revealed in the form of delayed latencies.

Urbanization effects on growth and otolith asymmetry in Chrysichthys nigrodigitatus and Oreochromis niloticus within tropical coastal lagoon watersheds.

In this study, we investigated the growth dynamics and otolith shape asymmetry of two fish species, Chrysichthys nigrodigitatus (CN) and Oreochromis niloticus (ON), within urbanized watersheds of the southern lagoon system, Nigeria. Using the von Bertalanffy growth model (VBGM), in addition to sediment metal concentration indices such as the average shale content, index of geoaccumulation (Igeo), contamination factor (CF), pollution load index (PLI), and potential ecological risk (PER) index, contamination levels were classified, and ecological risks were assessed. Notably, a lower growth potential (t0) was observed in CN at Ikorodu than at Epe, with similar trends for ON in the Epe during the dry season. Otolith asymmetry patterns, particularly in the CN at Ikorodu and ON in the Epe during the dry season, exhibited distinct ecological variations, indicating heightened stress levels at Ikorodu. Sediment analyses revealed moderate to strong contamination (Cd, Pb, Ni, and Cr) in both Lagos Lagoon (Ikorodu) and Epe Lagoon, with Ikorodu exhibiting notably high to moderate contamination levels according to the CF index. Elevated PLI values for Cd and Pb in Ikorodu, in addition to greater PER, indicated increased risk, with Cd posing a high risk (61.42%) and Pb posing a moderate risk (49.50%). Additionally, the reduced asymptotic length in the Epe during the dry season suggests that Chrysichthys nigrodigitatus is adaptable to seasonal variations, while divergent growth patterns in both areas indicate the existence of trade-off mechanisms in response to changing conditions. Habitat-specific otolith asymmetry and metal contamination underscore species adaptability, with wider stressor variability in Lagos than in Epe. Furthermore, multidimensional scaling analysis highlights the intricate relationship between otolith shape variables and environmental factors, emphasizing the need for tailored conservation efforts in urbanized watersheds.

The incorporation of strontium and barium into the otoliths of the flounder Paralichthys olivaceus at early life stages demonstrates resilience to ocean acidification.

Ocean acidification could modify the bioavailability and chemical properties of trace elements in seawater, which could affect their incorporation into the calcareous structures of marine organisms. Fish otoliths, biomineralized ear stones made by aragonite, are suspended within the endolymph fluid of teleosts, indicating that the elemental incorporation of otoliths might also be susceptible to ocean acidification. In this study, we evaluated the combined effects of CO2-induced ocean acidification (pH 8.10, 7.70, and 7.30, corresponding to ocean acidification scenarios under the representative concentration pathway 8.5 model as projected by the Intergovernmental Panel on Climate Change) and water elemental concentrations of strontium (Sr) and barium (Ba; low, medium, and high) on elemental incorporation into otoliths of the flounder Paralichthys olivaceus at early life stages. Our results revealed that the elemental incorporation of Sr and Ba into otoliths was principally dependent on the corresponding water elemental concentrations rather than on ocean acidification. Moreover, the partition coefficients (DMe) of Sr and Ba may stabilize after dynamic equilibrium is reached as the water elemental concentration increases, but are not affected by ocean acidification. Therefore, the incorporation of Sr and Ba into otoliths of the flounder at early life stages may not serve as an effective indicator of ocean acidification. In other words, the findings suggest that ocean acidification does not impact the incorporation of Sr and Ba incorporation into otoliths when tracing the temperature or salinity experiences of the flounder. Our findings will provide new knowledge for understanding the potential ecological effects of ocean acidification on the recruitment dynamics of fish species.

Otolith morphogenesis during the early life stages of fish is temperature-dependent: Validation by experimental approach applied to European seabass (Dicentrarchus labrax).

Otolith shape is often used as a tool in fish stock identification. The goal of this study was to experimentally assess the influence of changing temperature and ontogenic evolution on the shape component of the European seabass (Dicentrarchus labrax) otolith during early-life stages. A total of 1079 individuals were reared in a water temperature of 16°C up to 232 days post hatch (dph). During this experiment, several specimens were transferred into tanks with a water temperature of 21°C to obtain at the end of this study four different temperature treatments, each with varying ratios between the number of days at 16 and 21°C. To evaluate the otolith morphogenesis, samples were examined at 43, 72, 86 and 100 dph. The evolution of normalized otolith shape from hatching up to 100 dph showed that there were two main successive changes. First, faster growth in the antero-posterior axis than in the dorso-ventral axis changed the circular-shaped otolith from that observed at hatching and, second, increasing the complexity relating to the area between the rostrum and the anti-rostrum. To test the effect of changing temperature, growing degree-day was used in three linear mixed-effect models. Otolith morphogenesis was positively correlated to growing degree-day, but was also dependent on temperature level. Otolith shape is influenced by environmental factors, particularly temperature, making it an efficient tool for fish stock identification.

[Evaluation of semicircular canal and otolith graviceptive pathway function in patients diagnosed with motion sickness disorder based on the diagnostic criteria of the Bárány society].

Objective: To investigate the altered function of the semicircular canal and otolith graviceptive pathway in patients diagnosed with motion sickness disorder (MSD) based on the diagnostic criteria of the Bárány society, and explore its relevance to the pathogenesis of MSD. Methods: This is a case-control study. Twenty patients with MSD and age-and sex-matched healthy controls without a history of MSD from the Department of Neurology of Aerospace Center Hospital between March and August 2022 were recruited. All subjects completed the motion sickness susceptibility questionnaire-short version (MSSQ-short) and the motion sickness assessment questionnaire (MSAQ). Canal function was evaluated using caloric stimulation test and video head impulse test (vHIT), and subjective visual vertical/horizontal (SVV/SVH) and vestibular evoked myogenic potential (VEMP) were employed to assess otolith graviceptive function. Differences in vestibular function and correlations between the two groups were analyzed. Results: Each group consisted of 20 cases (9 males and 11 females). The mean age of the MSD and control groups was (26.9±3.9) years and (27.0±3.4) years, respectively. The scores of MSSQ-short [27.0 (22.5, 38.8) vs 1.2 (0, 3.2), P<0.001] and MSAQ [70.1 (54.5, 78.1) vs 11.8 (11.1, 13.9), P<0.001] were significantly higher in the MSD group compared with those of the control group. Evaluation of canal function revealed a significantly higher incidence of caloric stimulation intolerance in MSD patients (60.0%, 12/20) compared with that of the control group (20.0%, 4/20) (P=0.010). Evaluation of otolith graviceptive pathway indicated no significant difference in SVV, SVH and cervical VEMP (cVEMP) abnormality rates between the two groups (all P>0.05). The ocular VEMP (oVEMP) abnormality rate was significantly higher in the MSD group (55.0%, 11/20) than that of the control group (10.0%, 2/20) (P=0.002), with a delayed P1-wave latency compared with the control group [(18.4±1.2) ms vs (17.6±0.8) ms, P=0.018]. Further correlation analysis revealed that P1-wave latency in oVEMP was positively correlated with MSSQ-short (r=0.486, P=0.002) and MSAQ (r=0.391, P=0.015) scores, and duration of caloric intolerance symptoms (r=0.377, P=0.004). Conclusion: The presence of hypersensitivity to caloric stimulation and delayed latency of otolith function in patients with MSD suggests a "separation" between semicircular canal and otolithic function, which may be related to sensory conflict.

[Comparison of efficacy between personalized vestibular rehabilitation and otolith reposition for the treatment of atypical benign paroxysmal positional vertigo].

Objective: To compare the clinical efficacy of personalized vestibular rehabilitation and otolith reposition in treating atypical benign paroxysmal positional vertigo (BPPV). Methods: A randomized controlled trial was carried out. Fifty patients diagnosed with atypical BPPV in the Vertigo Clinic of the First Affiliated Hospital of Shandong First Medical University from October 2022 to September 2023 were recruited and randomly divided into manual reduction group (25 cases) and vestibular rehabilitation group (25 cases) according to the random number table. All patients were given flunarizine. Patients in the manual reduction group were treated by Epley maneuver and (or) Barbecue maneuver, while the vestibular rehabilitation group was given personalized vestibular rehabilitation therapy. After two weeks' treatment, the clinical symptoms (positional vertigo/nystagmus) and total dizziness handicap inventory (DHI) score, DHI physical (DHI-P), DHI emotional (DHI-E), and DHI functional (DHI-F) of the two groups were evaluated and compared. Results: A total of 50 patients diagnosed with atypical BPPV were included, including 23 males and 27 females, with an average age of (48.8±14.5) years. There was no statistically significant difference between the two groups in age, gender, disease severity, Romberg, position test abnormality ratio (Dix-hallpike/Roll test), temperature test, and video head impulse test baseline test results (all P>0.05). After 2 weeks of treatment, the effective rates of the treatment in the manual reduction and vestibular rehabilitation groups were 56.0% (14/25) and 88.0% (22/25), respectively, with a statistically significant difference (P=0.025). The total DHI score, DHI-P, DHI-E, and DHI-F scores in both groups were significantly decreased after treatment (all P<0.001). Compared with the manual reduction group, the total DHI score (23.2±2.7 vs 36.4±15.7, P=0.002), DHI-P (10.2±4.6 vs 13.7±5.3, P=0.016) and DHI-F (6.5±6.4 vs 13.0±7.2, P=0.002) in the vestibular group were lower, however, there was no significant difference in DHI-E score between the two groups (6.6±4.8 vs 9.6±7.3, P=0.087). Conclusion: Compared with otolith reposition, personalized vestibular rehabilitation therapy plays a better role in improving the symptoms and decreasing DHI score for patients with atypical BPPV.

Numerical Simulations of the Epley Maneuver With Clinical Implications.

OBJECTIVES: Canalith repositioning procedures to treat benign paroxysmal positional vertigo are often applied following standardized criteria, without considering the possible anatomical singularities of the membranous labyrinth for each individual. As a result, certain patients may become refractory to the treatment due to significant deviations from the ideal membranous labyrinth, that was considered when the maneuvers were designed. This study aims to understand the dynamics of the endolymphatic fluid and otoconia, within the membranous labyrinth geometry, which may contribute to the ineffectiveness of the Epley maneuver. Simultaneously, the study seeks to explore methods to avoid or reduce treatment failure. DESIGN: We conducted a study on the Epley maneuver using numerical simulations based on a three-dimensional medical image reconstruction of the human left membranous labyrinth. A high-quality micro-computed tomography of a human temporal bone specimen was utilized for the image reconstruction, and a mathematical model for the endolymphatic fluid was developed and coupled with a spherical particle model representing otoconia inside the fluid. This allowed us to measure the position and time of each particle throughout all the steps of the maneuver, using equations that describe the physics behind benign paroxysmal positional vertigo. RESULTS: Numerical simulations of the standard Epley maneuver applied to this membranous labyrinth model yielded unsatisfactory results, as otoconia do not reach the frontside of the utricle, which in this study is used as the measure of success. The resting times between subsequent steps indicated that longer intervals are required for smaller otoconia. Using different angles of rotation can prevent otoconia from entering the superior semicircular canal or the posterior ampulla. Steps 3, 4, and 5 exhibited a heightened susceptibility to failure, as otoconia could be accidentally displaced into these regions. CONCLUSIONS: We demonstrate that modifying the Epley maneuver based on the numerical results obtained in the membranous labyrinth of the human specimen under study can have a significant effect on the success or failure of the treatment. The use of numerical simulations appears to be a useful tool for future canalith repositioning procedures that aim to personalize the treatment by modifying the rotation planes currently defined as the standard criteria.

Post-settlement dynamics of Japanese flounder Paralichthys olivaceus in Tango Bay: Seasonal patterns in growth, mortality, and recruitment potential.

Japanese flounder Paralichthys olivaceus is one of the most valuable coastal flatfish species in East Asia. To investigate post-settlement growth and mortality, juveniles were sampled in Tango Bay (Japan) weekly throughout the settlement period in 2007 and 2008. Otolith (lapillus) microstructure analysis enabled the categorization of juveniles into six biweekly cohorts each year. Later cohorts exhibited higher growth rates possibly because of higher water temperatures. A key observation was the direct relationship between high mortality and high density in mid-season cohorts in both years, pointing to density-dependent mortality. This increased mortality may be attributed to predation, including cannibalism by earlier cohorts. Furthermore, growth-selective mortality was evident soon after settlement, underscoring the vulnerability of slow growers to predation during the early juvenile stage. Although earlier and later cohorts were less abundant but showed promising recruitment potential, the prospective contribution of mid-season cohorts to the adult population remained uncertain. The results clearly highlight the importance of density-dependent mortality in population regulation in post-settlement Japanese flounder.

Intra-population variability of the saccular, utricular and lagenar otoliths of the garfish Belone belone (Linnaeus, 1760) from South-Western Ionian Sea (Central Mediterranean Sea).

The garfish Belone belone represents the only valid endemic Belone species for the Mediterranean Sea and the eastern Atlantic Ocean. It shows a wide global distribution range, with a high commercial value and ecological relevance in the pelagic domain. Despite this, there needs to be more knowledge regarding the otoliths of this species, with the total absence of descriptions regarding asterisci and lapilli from Mediterranean populations and a lack of studies on the reliability of shape analysis on its sagittae. The present paper aims to provide the first main contours description of the three otoliths pairs from a Mediterranean population, providing an accurate investigation of morphology, morphometry, and intra-specific variability of sagittae, lapilli, and asterisci. Results showed (i) the absence of directional bilateral asymmetry and sexual asymmetry for the three otoliths pairs, (ii) a different morphology and morphometry of sagittae, lapilli and asterisci than those described in the literature, and (iii) an enhanced variability between sagittae morphometry and shape between the three investigated size classes. All these data confirmed the reliability of the studied species of shape analysis, showing a geographical and size-related variability of otoliths features probably related to genetics, environmental conditions, and life habits variations.

Quantifying larval dispersal portfolio in seabass nurseries using otolith chemical signatures.

The temporal asynchronies in larvae production from different spawning areas are fundamental components for ensuring stability and resilience of marine metapopulations. Such a concept, named portfolio effect, supposes that diversifying larval dispersal histories should minimize the risk of recruitment failure by increasing the probability that at least some larvae successfully settle in nursery. Here, we used a reconstructive approach based on otolith chemistry to quantify the larval dispersal portfolio of the European seabass, Dicentrarchus labrax, across six estuarine nursery areas of the northeast Atlantic Ocean. The analysis of natal and trajectory signatures indicated that larvae hatch in distinct environments and then dispersed in water masses featured by contrasting chemical signatures. While some trace elements appeared affected by temporal changes (Mn and Sr), others varied spatially during the larval stage but remained poorly affected by temporal fluctuation and fish physiology (Ba, Cu, Rb and Zn). We then proposed two diversity metrics based on richness and variations of chemical signatures among populations to reflect spatio-temporal diversity in natal origins and larval trajectories (i.e., estimates of dispersal portfolio). Along the French coast, the diversity estimates were maximum in nurseries located at proximity of offshore spawning sites and featured by complex offshore hydrodynamic contexts, such as the Mont St-Michel bay. Finally, our findings indicate that the dispersal portfolio was positively related with the local abundance of seabass juveniles, supporting the assumption that heterogeneity in dispersal history contributes to promote recruitment success in nurseries.

I spy: Factors influencing the observation of oxytetracycline in calcified structures of fishes viewed using standard light and fluorescence microscopy.

The antibiotic oxytetracycline (OTC) is a fluorochrome marker, and fluorescence microscopy is used to view OTC marks in fishes' calcified structures. However, OTC marks have been observed in calcified structures using standard light microscopy for multiple species. Therefore, we conducted an experiment to investigate potential factors (i.e., season, total length of fish, growth rate, and sex) influencing the observation of OTC in calcified structures (otoliths and fin rays or spines) from channel catfish Ictalurus punctatus, gray redhorse Moxostoma congestum, Guadalupe bass Mircopterus treculii, and redbreast sunfish Lepomis auritus viewed using standard light and fluorescence microscopy. OTC stains were not observed in any otoliths under standard light; however, OTC marks were commonly observed in I. punctatus spines using standard light microscopy (56.2%). Ninety-nine percent of otoliths and 88.9% of spines and fin rays had a visible fluorescent OTC mark when viewed using fluorescence microscopy. There was a negative relationship between the observed OTC mark and total length of fish for each season, but fish injected in the summer had the most structures with an observed OTC mark under either light condition. Understanding how OTC marking is affected by biological processes and environmental conditions will assist in future studies that rely on chemical marking of calcified structures by increasing efficacy of OTC marking and interpretation of marks.

Daily age, growth rate, and pelagic larval duration of commercially important snapper species in Abrolhos National Marine Park.

The age and daily growth of fish are registered through the deposition of increments in their otoliths, which are concretions formed by the precipitation of substances present in the endolymphatic fluid, mainly calcium carbonate (CaCO3). Faced with the need to fill some of the gaps in the knowledge on the occurrence and duration of the initial stages of snapper species' life cycles in the Abrolhos Bank, this study aimed to describe the growth rates, age, and period of pelagic larval duration (PLD) of three snapper species during the larval pre-settlement phase, in the Abrolhos Bank region. The post-larvae were captured using light traps. Otoliths were removed from 117 samples of snapper species; however, only 69 were viable for age estimation, of which 15 were Lutjanus analis, 25 were Lutjanus jocu, and 29 were Lutjanus synagris. Together, the samples presented individuals with total lengths ranging from 16.14 to 24.76 mm and ages from 21 to 39 days. Settlement marks were found for all three species, and the average PLD was ~25 days. The somatic growth of the snapper species was positively correlated with otolith growth. L. jocu presented the greatest daily growth compared to the other species. The three species use the Abrolhos Bank as a larval settlement site, demonstrating plasticity by using different habitats throughout their lives.

Morphometry and morphology of fish otoliths on the coast of the state of Maranhão, Brazil.

The main objective of this study was to evaluate the biometric relationships between the species Bagre bagre, Lutjanus synagris and Nebris microps and their otoliths. The relationship between the size of the otolith (length and weight) and the size of the fish (standard length and total weight) was determined using the linear regression model (y = a + bx). For the morphological description, the otoliths of three specimens were selected by standard length class (10mm). The morphological characters analyzed were chosen according to traditional literature. Three hundred eight specimens of B. bagre, 200 of L. synagris and 237 of N. microps were analyzed. Throughout the collection period, the source of the capture of individuals was the municipality of Raposa. The linear correlations for fish and otolith length for B. bagre were 0.9129 and 0.9652, respectively. For L. synagris, the coefficients were 0.8634 and 0.8672, while for N. microps, 0.9597 and 0.8636, respectively. The morphological classification of L. synagris and N. microps is of the Saggita type, and the B. bagre species is of the Lapillus type. From the data presented here, it is possible to observe that otolith morphometric and morphological data can serve as a parameter to estimate the relationship between the fish and the otolith in terms of its biomass and the length of an individual and a population.

Diagnostic value of vestibular evoked myogenic potentials in benign paroxysmal positional vertigo.

OBJECTIVES: Vestibular evoked myogenic potentials (VEMPs) are useful for studying the disturbances along nerve pathways implicated in the transmission of neurological information from otolithic organs related to vestibular function. This study aims to determine the differences in VEMPs in patients affected with benign paroxysmal positional vertigo (BPPV). METHODS: We recruited 36 patients, 9 diagnosed with recurrent BPPV (rBPPV), 9 with only one episode of vertigo (iBPPV), and 18 as a control group. We performed cervical and ocular VEMPs (cVEMPs and oVEMPs). RESULTS: We observed differences in asymmetry ratio, which was 41.82% in cVEMPs in iBPPV and 68.27% in oVEMPs in rBPPV, while no asymmetry was found in control cases. Also, there was a lack of both VEMP responses in 22.2% of cases and an absence of cVEMP in 11.1% in iBPPV; in rBPPV, 11.1 % presented no responses in cVEMPs or oVEMPs, 22.2% showed no oVEMP, and 11.1% showed no cVEMP. These values were normal in the control group. CONCLUSION: The value of VEMPs in BPPV demonstrates the implication of vestibular damage, mainly utricle damage. For better sensitivity in detecting otolith abnormalities, we should perform oVEMPs and cVEMPs in recurrent BPPV and early stages of BPPV.

Otolith sectioning reveals higher maximum age in greater weever (Trachinus draco).

Growth and maximum age are two key parameters that inform resilience of fish populations to exploitation. Existing information on those for greater weever inhabiting the eastern North Sea is based on the analysis of whole otoliths. Here, we present a reanalysis using sectioned otoliths. The results reveal a different growth pattern and a higher maximum age than that previously reported. The higher maximum age makes greater weever populations more vulnerable to exploitation. Such information can serve as a basis for the estimation of the growth curve that can be used for future assessment of the species.

Isotopes and otolith chemistry provide insight into the biogeochemical history of mercury in southern flounder across a salinity gradient.

Methylmercury (MeHg) continues to pose a significant global health risk to wildlife and humans through fish consumption. Despite numerous advancements in understanding the mercury (Hg) cycle, questions remain about MeHg sources that accumulate in fish, particularly across transitional coastal areas, where harvest is prominent and Hg sources are numerous. Here we used a unique combination of Hg and nutrient isotopes, and otolith chemistry to trace the biogeochemical history of Hg and identify Hg sources that accumulated in an economically important fish species across Mobile Bay, Alabama (USA). Fish tissue Hg in our samples primarily originated from wet deposition within the watershed, and partly reflected legacy industrial Hg. Results also suggest that little Hg was lost through photochemical processes (<10% of fish tissue Hg underwent photochemical processes). Of the small amount that did occur, photodegradation of the organic form, MeHg, was not the dominant process. Biotic transformation processes were estimated to have been a primary driver of Hg fractionation (∼93%), with isotope results indicating methylation as the primary biotic fractionation process prior to Hg entering the foodweb. On a finer scale, individual lifetime estuarine habitat use influenced Hg sources that accumulated in fish and fish Hg concentrations, with runoff from terrestrial Hg sources having a larger influence on fish in freshwater regions of the estuary compared to estuarine regions. Overall, results suggest increases in Hg inputs to the Mobile Bay watershed from wet deposition, turnover of legacy sources, and runoff are likely to translate into increased uptake into the foodweb.

Immunohistochemical and ultrastructural characterization of the inner ear epithelial cells of splitnose rockfish (Sebastes diploproa).

The inner ear of teleost fish regulates the ionic and acid-base chemistry and secretes protein matrix into the endolymph to facilitate otolith biomineralization, which is used to maintain vestibular and auditory functions. The otolith is biomineralized in a concentric ring pattern corresponding to seasonal growth, and this calcium carbonate (CaCO3) polycrystal has become a vital aging and life-history tool for fishery managers, ecologists, and conservation biologists. Moreover, biomineralization patterns are sensitive to environmental variability including climate change, thereby threatening the accuracy and relevance of otolith-reliant toolkits. However, the cellular biology of the inner ear is poorly characterized, which is a hurdle for a mechanistic understanding of the underlying processes. This study provides a systematic characterization of the cell types in the inner ear of splitnose rockfish (Sebastes diploproa). Scanning electron microscopy revealed the apical morphologies of six inner ear cell types. In addition, immunostaining and confocal microscopy characterized the expression and subcellular localization of the proteins Na+-K+-ATPase, carbonic anhydrase, V-type H+-ATPase, Na+-K+-2Cl--cotransporter, otolith matrix protein 1, and otolin-1 in six inner ear cell types bordering the endolymph. This fundamental cytological characterization of the rockfish inner ear epithelium illustrates the intricate physiological processes involved in otolith biomineralization and highlights how greater mechanistic understanding is necessary to predict their multistressor responses to future climate change.