Hypergravity decreases carbonic anhydrase-reactivity in inner ear maculae of fish

Previous investigations revealed that fish inner ear otolith growth depends on the amplitude and the direction of gravity. Both otolith total size, otolith bilateral size-asymmetry and the total and bilateral calcium-incorporation are also affected by gravity. Hypergravity, e.g., slows down otolith growth and diminishes bilateral otolith asymmetry as compared to 1 g control specimens raised in parallel. Since the enzyme carbonic anhydrase (CA) plays a prominent role in otolithic calcification, the reactivity of inner ear CA during otolith growth under hypergravity was investigated. CA-reactivity was demonstrated histochemically and densitometrically on sections of inner ear maculae of larval cichlid fish (Oreochromis mossambicus), that were kept for 6 hrs in a 3 g hypergravity centrifuge. The total unilateral macular CA-reactivity and the bilateral difference in CA between the left and the right maculae were significantly lower in 3 g animals than in 1g controls. The result is in complete agreement with previous studies indicating that a regulatory mechanism, which adjusts otolith size and asymmetry towards the gravity vector, acts via activation/deactivation of macular CA.     

cost-effective method of preparing larval fish otoliths for reading using enzyme digestion and staining

A fast and cost-effective method for examining otoliths in fish larvae was developed whereby the otolith remains in situ . Whole fish of the clownfish Amphiprion melanopus were enzymecleared using a laundry pre-soak and then stained using the Von Kossa silver staining method for calcium. The otolith nucleus, daily rings and the otolith edge were all clearly visible and were suitable for a variety of age and growth analyses. The total 'hands on' time required to process these otoliths was c . 3 min, and multiple samples could be processed simultaneously. The reduction in labour of this method to produce clear daily rings in the otolith lends itself to broad use in fish biology where large quantities of otoliths need to be examined in a cost- and time-efficient manner.     

Functional asymmetry estimated by measurements of otolith in fish.

It is widely accepted that the incidence of space adaptation syndrome (SAS) is due to a mismatch of sensory information from various receptors to the central nervous system. We investigated the functional asymmetry of vestibular organ, which may caused sensory conflict in space, by measuring the weight difference of otolith between left and right side in goldfish and carp. In the goldfish utricular otolith, the maximum difference was 0.8 mg and the mean difference was 0.091 mg. The percentage of weight difference to the heavier otolith was calculated. The maximum difference was 20.57% and the mean was 3.035%. A difference exceeding 10% was found in only 2 goldfish. In the carp utricular otolith, the maximum percentage difference of weight was 24.8% and the mean was 3.491%. A difference exceeding 10% was found in only 3 carp. The maximum difference of saccular otolith was 11.8% with the mean of 6.92%, and that of lagenar otolith was 32% with the mean of 5.6% in goldfish. The close relationship of utricular otolith weight between both sides suggested that the otolith asymmetry might not be the main factor inducing SAS at least in goldfish and carp.     

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.

     

Temperature effects on otolith pattern formation in Atlantic cod Gadus morhua

The effect of food intake and temperature on otolith macrostructure and microstructure was examined experimentally in Atlantic cod Gadus morhua. Daily increment formation was validated and otolith accretion rate and optical density quantified using image analysis. Two‐week periods of starvation had no discernable effect on otolith increment width or optical density, despite having negative effects on somatic growth. In contrast, temperature had a strong positive effect on otolith accretion rate and clear effects on optical density with the otolith becoming more translucent at higher temperatures. Somatic growth, otolith accretion and otolith optical density each had a significantly different response curve to temperature. No relationship was detected between individual somatic growth rates and the accretion rate or optical properties of the otolith. The experimental manipulation of temperature‐induced otolith patterns similar to the ‘false ring’ secondary structures sometimes observed in the otoliths of wild fish. The results suggest that otolith pattern arises from a combination of temperature and seasonal effects, but not directly from individual variation in somatic growth.     

Variation in migratory history of Dolly Varden in a stream with an artificial dam in the Shiretoko Peninsula,Hokkaido, Japan

The variation of migration patterns in Dolly Varden Salvelinus malma in a stream with an artificial dam (erosion-control-dam) in the Shiretoko Peninsula, Hokkaido Island, Japan, at the southernmost part of its distribution, was examined by otolith Sr:Ca ratio analysis. All specimens from the above-dam area showed consistently low Sr:Ca ratios (<5.0 × 10⁻³) throughout the otolith. In contrast, many specimens from the below-dam area had higher ratios (>5.0 × 10⁻³) throughout the otolith or only at the outer part than do those from the above-dam area. This higher ratio is probably due to salinity effects. Specimen from the below-dam area could be divided into three types: (1) Consistently low Sr:Ca ratios throughout the otolith, being freshwater residents. (2) Low Sr:Ca ratios around the inner part of the otolith, and thereafter higher ratios toward the outer part, being typically anadromous. (3) Relatively higher Sr:Ca ratios throughout many or in some parts of the otolith, indicating that these have migrated from the freshwater to brackish water or seawater from the early life stage. These findings suggest that Dolly Varden has a high degree of plasticity in its migratory behavior.     

Otolith responses to dynamical stimuli: results of a numerical investigation

To investigate the dynamic effects of external forces on the displacement of the otolith membrane and subsequent neuronal responses of otoliths, we performed numerical analyses of otolith membrane displacements. In these studies we included the full geometry of the human otolith maculae, including their 3D curvature. The first part focuses on mechanical aspects of the otolith membrane. While it was found that the mechanical coupling of distant parts of the otolith membrane is only weak, these simulations indicate that curvature may have considerable local effects on displacements. They further suggest that the movements of the otoconia, embedded in the interotoconial matrix, show a resonance in a range between 100 and 2000 Hz. In the second part of the article we also investigate the tonic-phasic responses in the vestibular nerve emanating from hair cells in the striola region. Small head tilts away from head upright position are used. The simulations indicate that the direction of head tilt is coded in characteristic response patterns along the striola.     

鲫耳石重量与年龄的关系及其在年龄鉴定中的作用

耳石重量在年龄组间重叠较少,大小相近的个体,年龄大的,即生长慢的耳石重量比年龄小的,即生长快的大,不同龄组之间耳石重量有显著差异（P＜0．05）,按年龄组在耳石重量与相应的体长作图,可初步判断观测年龄的可靠性,分析耳石重量频率分布能分离出体长相近,年龄不同的个体,其结构与耳石年轮观测的基本一致,耳石重量与年龄呈显著线性正相关（P＜0．05）,用耳石重量与年龄关系估算的年龄从耳石上直接读取的年龄无显著差异（P＞0．05）,文中对耳石重量直接用于确定鱼类年龄的可能性作了分析和探讨。     

Effects of starvation on the formation of daily growth increments in the otoliths of milkfish, Chanos chanos (Forsskål), larvae

The effects of starvation on daily growth and increment formation in the otolith were examined using a double oxytetracycline-labelling method on larval milkfish, Chanos chanos (Forsskål), reared under different feeding regimes. The results indicated that the differences in body and otolith growth between the larvae fed once and three times a day were not significant, and that the otolith growth increment was deposited daily in both groups of fed larvae. In contrast, the starved larvae grew at a slower rate than fed larvae in body length and otolith dimensions, and the otolith growth increment in the starved larvae was not deposited on a daily basis. After undergoing starvation, the larvae were unable to recover their normal growth either in otolith increment deposition or in body and otolith growth even though they were fed. Therefore, the application of ageing techniques based on counting otolith growth increments seems to be inaccurate for starved larvae.     

Is otolith science transformative? New views on fish migration

Publications focused on fish otolith applications grew exponentially from 1981–2000 but have subsequently stabilized, suggesting maturation of otolith applications. Over the past 30 years >3,500 primary journal publications were identified prompting the question, how have otoliths fundamentally changed our understanding of fishes and their environment? Has otolith science in this way been transformative? I use Harden Jones’ 1968 Fish Migration as a benchmark of fish migration concepts prior to Pannella’s 1971 breakthrough paper on otolith microstructure. For case study species I highlight how otolith science has informed migration concepts including, (1) parent stream theory (Atlantic bluefin tuna), (2) adoptive homing (Atlantic herring), and (3) partial migration (European eel). Harden Jones’ overall conclusion that life cycle closure leads to population structure (also known as the migration triangle) is a first principle in fisheries science, but in recent years has been challenged by otolith science. In particular, a transformative discovery attributable to otoliths is that life cycles vary substantially within populations. New avenues of otolith science are now exploring the causes and consequences of this life cycle diversity, and large advances are expected through integration of otolith approaches with electronic tagging, genetics, field manipulations, and modeling that will permit migration concepts to be tested at multiple ecological scales.     

Unravelling the stock structure of the Persian brown trout by otolith and scale shape

The simultaneous use of the scale and otolith morphometry was assessed as a potential tool for the identification of Persian brown trout Salmo trutta stocks of the Lar Lake and five rivers from Lar Basin, Iran. Fourier coefficients (FC) and circularity, rectangularity, roundness, ellipticity and form factor shape indices (SI) were calculated for otolith and scale. Several SIs were significantly different among sites for both structures. Permutational multivariate analysis of variance revealed significant differences between several pairwise comparisons for otolith and scale (FCs and indices separately). Discriminant analysis showed otolith FCs (cross-classification rates: 25–86%) and SI (20–45%) appear to be a relatively acceptable tool to discriminate between several locations. Comparatively, the scale morphometry showed lower discriminatory power (FC = 3–65%; SI = 15–34%), with the exception of SI for Elarm River (60%), Kamardasht River (56%) and Lar Lake (75%). Cross-classification rates improved up to 100% when discriminate analysis incorporating all variables for otolith and scale was performed. The results showed a potential segregation between some water bodies, suggesting that the otolith and scale morphometry could be a useful tool to delimit S. trutta populations in relatively close freshwater environments.     

Characterization and variations of organic parameters in teleost fish endolymph during day-night cycle, starvation and stress conditions

The aim of the present work was to examine the modifications of the organic composition of fish endolymph under environmental conditions (day-night cycle, starvation and Cl2-stress) known to modify otolith growth. Endolymph electrophoretic patterns were compared. An antibody raised against the trout otolith organic matrix allowed examining the variations of organic matrix precursors in the endolymph under the above conditions. Western blot analysis showed bands around 60-80 kDa. A 50% decrease of immunolabelling was observed during the night whereas increases were seen after starvation (factor 3) or stress (factor 2) suggesting that these variations could be related to the organic matrix deposit. A factor retarding in vitro CaCO3 crystallization (FRC) was shown to co-precipitate with endolymph proteins and its apparent molecular mass (determined by measuring the activity after electro elution of gel electrophoresis) was estimated around 20 kDa. The FRC activity was stable during day-night cycle whereas it decreased by 70% and nearly 100% under starvation and stress respectively. These results suggest that the FRC, although retarding in vitro crystallization, plays a major role in the process of otolith calcification and that the decreases measured after starvation and stress are responsible for the decreases of the otolith growth. The variations of these two parameters (precursors and FRC) could contribute for the changes in the microstructure of the otolith.     

Comparison of otolith growth and morphology with somatic growth and age in young-of-the-year bluefin tuna

Otolith morphological characteristics were studied using image analysis techniques and the relationships between otolith growth and somatic growth and age, as estimated from counting daily otolith increments, were examined in young-of-the-year (YOY) bluefin tuna Thunnus thynnus ranging in fork length ( L _F) from 8·5 to 55·5 cm. Whole otolith length, width, area and perimeter, and three shape indexes, circularity, E value and rectangularity, were extracted for each pair of sagittae. Since no statistical significant differences between left and right otolith morphometrics were found, only one otolith from each fish was used for correlations. Statistically significant relationships were observed between otoliths measurements and fish somatic growth when a linear regression was applied after logarithmic transformation of all variables tested. Among the variables, otolith length was the one that showed the highest correlation with L _F, followed by otolith area and perimeter, whereas otolith rectangularity exhibited the lowest correlation. Statistically significant relationships were also observed between the otolith variables tested and the age of the fish, which ranged from 20 to 129 days. The ages estimated using otolith mass were very close to those assessed using daily increment counts (bias ranged from 1 to 24 days). Therefore, otolith mass could represent a valuable criterion for age estimation in YOY bluefin tuna that is objective, economic and easy to perform compared to daily increment counting method.     

Bromine patterns in Norwegian coastal Cod otoliths—a possible marker for distinguishing stocks?

Bromine was found to accumulate in otoliths of Norwegian coastal Cod Gadus morhua that were reared under known conditions. Despite the fact that the Cod were moved from one rearing environment to another, causing marked changes in some otolith elemental concentrations, bromine appeared to accumulate continuously along certain growth axes as revealed by 2-D elemental mapping. In contrast, North Sea and Baltic Sea Cod showed little to no patterning in Br. We suggest that Br uptake in otoliths may be under physiological and genetic control, and as such, may prove useful as a stock identification tool.     

Otolith mass marking techniques for aquaculture and restocking: benefits and limitations

The use of farmed and restocked fish to supplement the worldwide human consumption of fish, recreational fishing stocks, and conservation efforts, is growing at a rapid rate. Yet, monitoring the benefits of using hatchery-raised fish for supplementation is lacking, often due to hatcheries not marking or tagging all fish prior to release, despite a range of easy to apply, cost effective and accurate mass-marking methods being available to mark farmed and restocked fish en masse. Here we review otolith marking techniques that have the capability of mass marking millions of hatchery-reared fish that are, or could be, used for monitoring and compliance purposes. The otolith mass marking methods consist of otolith thermal marking and a range of otolith chemical marking methods (tetracyclines, alizarin compounds, calcein, strontium chloride, stable isotopes of Ba and Sr, and rare earth elements). We assessed and compared marking technique in terms of (1) ease of application, (2) cost of application, (3) mark retention and detectability, and (4) fish welfare. In addition, we determine the suitability of different otolith marking techniques for mass marking entire hatchery populations whether it be for restocking purposes, or for identifying and tracing escapees from aquaculture facilities. We conclude that although some techniques have restricted use due to regulations, the majority of otolith mass marking techniques are simple, easy to apply, cost effective and highly suitable for long term monitoring of hatchery produced fish.     

Alterations in rat horizontal vestibulo-ocular reflex phase as a function of orientation in gravity

The effect of changes in static and dynamic gravity signals on the phase accuracy of the horizontal vestibulo-ocular reflex (HVOR) was studied in rats using chronically implanted scleral search coils to monitor eye movements. Rats were sinusoidally rotated using a range of different frequencies (0.035-2 Hz) in a plane which always activated the horizontal semicircular canals but in one of three different orientations with regard to gravity which differentially activated the otolith organs: 1) upright-normal static gravity signal, no dynamic otolith activation; 2) inverted-inverted static gravity signal, no dynamic otolith activation; 3) on-side-dynamic activation of the otolith organs. In the upright orientation, the HVOR shows a phase advance at 0.2 Hz and below but not at 0.5 Hz and above. Phase accuracy of the HVOR was further degraded in the inverted orientation with rats showing large phase leads at 0.2 Hz and below. In contrast, accuracy of the HVOR was significantly improved at 0.2 Hz and below in the on-side orientation with phase accurate eye movements down to the lowest frequency tested. The results further support the idea that otolith organs play an important role in VOR generation by supplementing the semicircular canals' response to angular head movements.     

Otolith crystals (in Carapidae): growth and habit

The biomineralization of otoliths results mainly from the release of soluble Ca(2+), which is in turn precipitated as CaCO(3) crystals. In some Carapidae, sagittae sections have been shown to reveal a three-dimensional asymmetry with a nucleus close to the sulcal side, an unusual position. This study seeks to understand otolith formation in Carapus boraborensis. The unusual shape of the otolith is partly explained by the distribution of the epithelium cells, and particularly the sensory epithelium. Experimental evidence shows for the first time that aragonite growth takes place along the c-axis. These aragonite needles present two different habits. On the sulcal side is found the acicular form resulting from rapid growth during a short period of time. On the anti-sulcal side, the prismatic form seen there is due to a slower growth speed over longer periods. The otolith surface was observed each hour during a period of 24h in fishes reared in similar conditions. This allowed for the first time the direct observation on the otolith surface of the deposition of the two layers (L-zone and D-zone). In C. boraborensis, the organic-rich layer (D-zone) develops during the day, whereas the CaCO(3) layer (L-zone) seems to be deposited during the night.     

Otolith oxygen and carbon stable isotopes in wild and laboratory-reared plaice (Pleuronectes platessa)

The relationship between water temperature, growth rate, and otolith isotopic ratios was measured for juvenile plaice (Pleuronectes platessa) reared at two temperatures (11 and 17°C) and two feeding regimes (1 and 3 prey items·ml^?1). The otolith isotope ratios in individual fish ranged from ?2 to ?4 for carbon isotope ratios (δ¹³C) and from 0.2 to 1.9 for oxygen isotope ratios (δ¹⁸O). The otolith oxygen isotope ratios were significantly affected by water temperature, but not by feeding level, and there were no significant synergistic effects. The fractionation of oxygen isotopes during otolith growth was independent of individual growth rate. Carbon isotope ratios were not significantly affected by food ration or water temperature, but were related to fish growth rate. The carbon isotope ratios were negatively correlated with fish length in the colder water treatments, and tended to increase with fish length in the warm water treatments. The laboratory-determined relationship between otolith oxygen isotope ratio and water temperature was applied to individuals of five species (plaice, cod, whiting, haddock, gurnard) collected in a single trawl sample. The otolith derived temperatures often overestimated measured water temperatures. The difference between real and estimated water temperatures varied between species, and the closest fit was for field-caught plaice.     

An eco-morphological explanation of individual variability in the shape of the fish otolith: comparison of the otolith of Hoplostethus atlanticus with other species by depth

Variation in otolith shape (otolith polymorphism) in Hoplostethus atlanticus, Hoplostethus mediterraneus, Paratrichichthys trailli, Pagrus major and Trachurus murphyi , quantified using principal components analysis based on Fourier transform decompositions of outlines of otolith shape, was particularly high among the samples of H. atlanticus from the North Atlantic, New Zealand, Australia and Namibia. The scatter was uniform, however, and did not show any significant differences among regions. The implication drawn from the high variability in otolith shape of H. atlanticus was that otolith shape polymorphism was maintained by some form of balancing selection across many small local environments which may result in k-selection with consequent poor response by H. atlanticus to maximum sustainable yield harvesting strategies. The variation in otolith shape defined by the otolith morphospace of the five species that were measured, showed a decreasing trend in scatter (i.e. decreasing complexity of shape) proceeding from the species with the deepest habitat ( H. atlanticus ) to the most shallow ( T. murphyi ).     

Otolith elemental signatures reflect residency in coastal water masses

We examined variability in otolith chemistry of wild caught fish in relation to in situ temperature and salinity within the California Current System. Barium, magnesium, and iron from the most recent growth zone in otoliths differentiated pelagic juvenile shortbelly rockfish (Sebastes jordani) residing in water masses with distinct temperature and salinity properties from central and southern California spanning nearly 500 km of coastline. The 3-element signature also discriminated fish that resided in different water masses that were associated with mesoscale cyclonic eddy circulation in the Santa Barbara Channel. Variability in otolith chemistry reflected the spatial patterns of both horizontal gradients and vertical gradients in water mass properties related to circulation. Although we found that the concentrations of particular elements in otoliths were correlated to ambient temperature or salinity, we suggest that these parameters are more useful as an identifying signature of distinct water masses associated with unique otolith signatures rather than as factors directly affecting otolith chemistry. Other factors varying among the water masses or among the fish populations residing in the water masses may also affect otolith chemistry. We discuss how oceanographic phenomena associated with the 1997–1998 El Niño and the persistent, recirculating eddy in the Channel may have affected coastal ocean conditions and variation in otolith chemistry of fish in the study area.