Otolith Morphology Research Articles

Otolith morphology and microchemistry fingerprints of European eel, Anguilla anguilla (Linnaeus, 1758) stocks from the Adriatic Basin in Croatia and Montenegro

Morphological and elemental composition of otoliths are a promising tool for fish stock identification. In this regard, European eel has not been sufficiently researched. The aim of this study was to determine otolith shape index values and microchemistry composition of 14 elements in otoliths of European eel between riverine and lacustrine stocks from the Adriatic Basin in Croatia and Montenegro. In terms of morphometry, the shape indices, form factor and circularity of the sagittal otolith were statistically different between lacustrine and riverine stocks. The European eel is considered to have a small otolith relative size. Canonical variate analysis indicated no statistical differences among the concentrations of trace elements in sagittal otoliths between riverine and lacustrine stocks. However, constrained redundancy analysis suggested a stronger relationship of width, total length, females and the silver stage with the Sr/Ca, Cr/Ca, Ba/Ca and K/Ca ratios of specimens from riverine than lacustrine habitats. Gender and stage dependent variations showed that females were better indicators of relationships between microchemistry composition and intrinsic factors. In conclusion, form factor and circularity of the sagittal otolith was able to distinguish between European eel stocks from different habitats. Also, it seems that the European eels' otolith fingerprint is homogenous, species specific and independent of ecological conditions.

Morphological study of otoliths of Antimora microlepis and Antimora rostrata (Actinopterygii: Gadiformes: Moridae)

A comparative morphological investigation of otoliths from two species of Antimora, A. microlepis and A. rostrata was conducted to identify distinguishing species-specific characteristics. Some of the identified characters were shared between the two species studied. Ontogenetic changes in otolith morphology of the two morids studied were evident between small and larger specimens. Otoliths of small-sized individuals have shown the same degree of similarity with the large-sized individuals.

First documentation of the otoliths of the species of Gouania (Teleostei: Gobiesocidae) in the Mediterranean Sea.

Otolith morphology is a widely accepted tool for species identification in teleost fish, but whether this holds true for very small species remains to be explored. Here, the saccular otoliths of the cryptobenthic Mediterranean clingfish Gouania (Gobiesocidae) are described for the first time. The new data, although preliminary, indicate that otolith morphology and morphometry support the recognition of the recently differentiated five species of Gouania in the Mediterranean Sea. Furthermore, otoliths of phylogenetically closely related Gouania species resemble each other more than do those of the more distantly related species.

Discrimination of species and populations of the genus Cichla (Cichliformes: Cichlidae) in rivers of the Amazon basin using otolithic morphometry

ABSTRACT The genus Cichla is a highly diverse group, with 16 species already described. Externally, some species are very similar and discriminating between them may be very difficult. Nevertheless, discrimination of fish stocks is essential for management purposes. Morphometric analyses of otoliths have been successfully used to distinguish species and fish stocks, especially in marine environments. This study evaluated whether sagittal otolith shape can be used to discriminate among the species Cichla temensis, C. monoculus, and C. orinocensis, as well as within populations of C. temensis in rivers of the Amazon. Shape indices and Fourier coefficients were used to describe the shape of the otoliths. Among the groups of species, the morphology of the sagittal otolith of C. temensis was totally distinct from the species C. monoculus and C. orinocensis. While among populations of C. temensis, individuals from the Negro and Jatapú Rivers were different, regardless of the methods used. These results confirm the ability to differentiate species and populations by using the morphology of otoliths. However, more research is needed to verify the role of genetic versus environmental and biotic effects, and thus be able to explain the discrimination observed in otoliths.

Otolith Morphology: A Hidden Tool in the Taxonomic Study of Goatfishes (Teleostei: Perciformes: Mullidae).

Goatfishes (Teleostei, Mullidae) are a group of mainly coastal fishes that form an important part of food chains, and also have commercial value. In the marine waters of Iran, they are found in the Persian Gulf and Oman Sea (Gulf of Oman). This study evaluated whether otolith morphology can be used to distinguish of species and genera, and also to interpret whether otoliths of the same species differ among two studied marine systems. To do this objective, the otolith morphology of ten species belonging to three genera were analyzed by SEM photography and shape analysis. Among the morphometric variables, relative rostrum length was found to be the most important otolith variable for discriminating Mulloidichthys (RRL = 32.29 ± 0.59) and Parupeneus (RRL = 37.39 ± 1.10), while rectangularity (REx) was the most important shape index for discriminating Mulloidichthys (REx = 0.99 ± 1.94) from Parupeneus (REx = 0.77 ± 1.21). By considering otolith morphology, Upeneus showed a better separation than the two other genera. The otoliths of Upeneus are diagnosed by short dorsal length (RDL = 69.35 ± 1.51), higher rostrum height (RRH = 53.63 ± 1.99), short rostrum (RRL = 31.12 ± 1.99), and antirostrum lengths (RanL = 12.38 ± 1.51). The most diverged phenotype within the genus Parupeneus was found for the otoliths of P. rubescens, and the most diverged phenotype within the genus Upeneus was found for the otoliths of U. sundaicus. The otoliths of the same species did not demonstrate large variation between the Persian Gulf and the Gulf of Oman. This study provides additional morphological evidence for the separation of goatfishes at the species and genus levels. We also underline that the slight observed differences between the otoliths of two marine systems are mainly caused by the ecological differences known between these two main systems.

Comparative analysis on otolith shape of <italic>Champsocephalus gunnari</italic> and <italic>Cryodraco antarcticus</italic> based on four morphological techniques

To study the effectiveness of otolith morphological techniques on the population classification of Antarctic ice fish, based on the collected samples of <italic>Champsocephalus gunnari</italic> and <italic>Cryodraco antarcticus</italic>, 5 kinds of basic otolith morphological parameters were measured and converted into 7 morphological indicators, the differences in otolith morphology of two species were compared and analyzed, principal component analysis (PCA), stepwise discriminant analysis (SDA) and random forest (RF) were then used to discriminate the 77 elliptical Fourier harmonics of otolith morphological parameters. The results showed that the otolith parameters and body length of two species were significantly correlated (<italic>P</italic>>0.05). The body length of <italic>C</italic>. <italic>gunnari</italic> showed a power function relationship with some morphological parameters. While otolith length, otolith height, otolith area, otolith perimeter, otolith mass of <italic>C</italic>. <italic>antarcticus</italic> were all in logarithmic relationship with the body length. It could be seen that the otolith ring rate of <italic>C</italic>. <italic>gunnari</italic> was lower than that of <italic>C</italic>. <italic>antarcticus</italic>, compared to the otolith of <italic>C</italic>. <italic>antarcticus</italic>, the otolith of <italic>C</italic>. <italic>gunnari</italic> was rounder and more regular. The conventional morphological analysis could not discriminate the otoliths of two species. The PCA could discriminate the otoliths of two species, and the discriminant success rates of SDA and RF were 98.78% and 91.67%, respectively. SDA has its advantage in small sample size, but RF is suitable for large sample size.

Otolith Morphology and Relationships of Several Fish Species of the Suborder Scorpaenoidei

Otolith (sagitta) morphology is described in six tropical fish species belonged to different genera of the suborder Scorpaenoidei: Synanceia horrida, Inimicus sinensis, Parascorpaena picta, Sebastapistes cyanostigma, Scorpaenopsis papuensis, and Dendrochirus zebra. Based on otolith shape (six shape indices and elliptic Fourier analysis), S. horrida is similar to Sc. papuensis and I. sinensis is similar to D. zebra. A comparison of otolith shape in P. picta, D. zebra, and three species of the family Sebastidae (Helicolenus dactylopterus, Sebastes semicinctus, and S. hopkinsi) using elliptic Fourier and principal component analyses shows that the clusters of H. dactylopterus and S. semicinctus partly overlap with the cluster of D. zebra, and the cluster of S. hopkinsi partly overlaps with the cluster of P. picta. The data on otolith shape do not correspond with current phylogenetic schemes that indicates relative independence of the inner ear evolution.

Dieta y amplitud del nicho trófico del cormorán neotropical [Nannopterum brasilianus (Gmelin, 1789)] en el Santuario de Flora y Fauna Ciénaga Grande de Santa Marta, Caribe de Colombia

El cormorán neotropical (Nannopterum brasilianus) es un ave piscívora con reproducción colonial. Se distribuye desde el sur de Norteamérica hasta Argentina. La colonia más grande en Colombia se encuentra en la localidad de Punta Blanca, localizada en el Santuario de Flora y Fauna Ciénaga Grande de Santa Marta (SFF CGSM), en el complejo lagunar del mismo nombre (CL CGSM). En el presente estudio se analizó la dieta y la amplitud de nicho de N. brasilianus a partir de egagrópilas recolectadas en el borde occidental de la colonia de anidación de Punta Blanca durante la época reproductiva de 2017. La identificación de presas se basó principalmente en la morfología de los otolitos de peces encontrados en las egagrópilas (n = 64). Se identificaron ocho especies de peces en la dieta de N. brasilianus, de las cuales tres fueron nuevos registros para la dieta de la población del complejo lagunar (Mugil liza, M. curema y M. cephalus). Se destacó la representatividad de Cathorops mapale como principal presa consumida durante el estudio (89,5 % en número y 91,8 % en frecuencia de ocurrencia). Se observó una amplitud de nicho trófico estrecha (Levin’s de 0,002) y una dieta con baja equitatividad (q2 = 2,1), lo que corresponde a una respuesta adaptativa modelada por la disponibilidad de presas.

Differentiating morpho-functional patterns of the five most common deep-sea benthic anglerfishes (Lophiiformes) from Andaman and Nicobar Islands (eastern Indian Ocean)

Anglerfishes are widely distributed from shallow to deep-water habitats occupying different ecological niches. To explain this adaptability, we performed a morpho-functional study on common benthic anglerfishes inhabiting the Indian deep-sea waters. Sensory capabilities of species were examined using the morphology and morphometry of sagitta otoliths (related to detection sound and hearing) and eye size (related to visual communication). We also performed an analysis of the degree of functional niche overlap using fish body traits to understand the coexistence of species. Otoliths showed a morphological pattern similar to that of other anglerfishes: an archaesulcoid sulcus acusticus and variability in the irregularity of the dorsal margin. This last feature affected the allometric relationships between the otolith morphometry and fish length, as well as the otolith relative sizes of each species. The findings suggested that bigger otoliths are associated with the increase of depth distribution of species up to 1000 m, from which it decreases. Our hypothesis is that anglerfishes with irregular otolith shapes could be linked to more nocturnal feeding behaviour because they were characterized by greater eye sizes. The results also indicated interspecific significant differences in functional traits providing a low niche overlap. Therefore, our study supports the hypothesis of an environmental and ecological specialization of benthic anglerfishes.

Effects of suboptimal temperatures on larval and juvenile development and otolith morphology in three freshwater fishes: implications for cold water pollution in rivers

Temperature is a key determinant that governs fish survival, reproduction, growth and metabolism. In freshwater ecosystems, anthropogenic influences have resulted in acute and prolonged temperature changes which lead to lethal and sub-lethal impacts on the biota that occupy these environments. We assessed the effects of temperature on somatic and otolith growth and development of three species of native Australian freshwater fish (silver perch Bidyanus bidyanus, trout cod Maccullochella macquariensis and golden perch Macquaria ambigua) to simulate how thermal pollution from the release of unseasonably cold water from thermally stratified dams in Australian freshwater ecosystems may impact fish at critical life-history stages. Fish (31 days post-hatch) were exposed to four temperature treatments (13, 16, 20, 24 °C) for 30 days. Low temperatures resulted in reduced somatic growth, with no growth observed in silver perch and golden perch held at 13 °C over 30 days. Somatic growth was highest at the upper temperature of 24 °C. Morphological assessment of fish size reiterated that low water temperatures resulted in reduced body size, particularly in terms of body width and head size. Low temperatures were associated with reduced otolith growth in all species, however a somatic-otolith size relationship was maintained for all species in measures of otolith weight, area, length and perimeter. The sub-lethal impacts observed in our study are likely to manifest at the population level through a reduced capacity of larvae and juveniles to avoid size-dependent predation, a narrower range of prey sources due to extended gape-limited feeding and, ultimately, poorer survival and recruitment.

Differences in otolith shape and fluctuating-asymmetry between reared and wild gilthead seabream (Sparus aurata Linnaeus, 1758).

Otolith structure is a useful tool in discrimination among fish populations as it is a permanent record of the influence of endogenous and exogenous factors. In the present study we examined otolith morphology and fluctuating asymmetry (FA) for differences between wild-caught (by bottom trawl) and reared specimens of Gilthead seabream (Sparus aurata). Based on the frequency of regenerated scales (degree of scale regeneration, SRD) on each specimen, a threshold of 30% SRD was used to assign wild-caught fish individuals as wild (≤30% SRD, LR group) or as possible aquaculture escapees (>30% SRD, HR group). Based on the analysis of elliptic Fourier descriptors, significant differences were found in otolith shape between reared (Rr) and the wild-caught groups (LR, HR). Reared fish had otoliths with significantly larger perimeter (OP ) than wild-caught fish. Furthermore, FA was significantly higher in the Rr than the LR group for OP and all except one shape descriptors (harmonics 2-7). The HR group exhibited intermediate levels of FA between the low and high FA levels observed in the LR and Rr groups. Results are discussed in terms of the value of combining otolith and scale morphology for the identification of escapees in wild Gilthead seabream stocks.

Delineation of seven species of genus Channa from upper Assam region, India using sagittal otolith morphology

Morphology of sagittal otoliths of seven species of genus Channa from upper Assam, India was studied to obtain baseline information for their prospective role in taxonomic studies. In the present study, variations were recorded in morphological characteristics of sagittal otolith among the studied species. Of all the studied parameters, otolith shape, sulcus acusticus, ostium, and cauda, in particular, were found to be taxonomically important features for the identification of the species. The pentagonal shape of sagitta in Channa punctata, pseudo-ostiocaudal sulcus acusticus in C. marulius, bent concave ostium in C. stewartii, straight cauda in C. bleheri were found to be species-specific features. Sagitta size was smallest in C. gachua while the largest was recorded in C. striata. The proposed taxonomic keys enumerated through the combination of different otolith characters from the present investigation will be useful in the identification of these species when standard methodologies fail to deliver satisfactory results.

The use of otolith shape to identify stocks of Konosirus punctatus

Konosirus punctatus is an important economic fish in the Northwest Pacific Ocean, especially along the coast of China, and an important substitute in the marine ecosystem. The aim of this study is to quantify the variation of sagittal shapes to discriminate the K. punctatus stocks between China coasts (Wei Hai, Yan Tai, Zhou Shan, Wen Zhou, Dong Ying, Hai Kou and Qing Dao) and Aomori (Am) in Japan by comparing the sagittal morphometric features. The sagitta variation of eight K. punctatus stocks was examined using nine shape indices (Roundness, Circularity, Form-factor, Rectangularity, Ellipticity, Radius ratio, Feret ratio, Aspect ratio and Surface density). Multiple comparisons on shape indices showed that three shape indices (Roundness, Feret ratio and Surface density) have significant differences between nine stocks. The comprehensive judgment accuracy rate is 54.5%. Based on the Fourier coefficient eight Fourier parameters can fit the shape of sagittal. The comprehensive judgment accuracy rate is 56.1%. The results showed that the otolith morphology was not significantly different between seven China stocks, while the China stocks showed a large sagittal morphological difference from the Japanese stock. It could be related to environmental factors and geographical conditions in various sea areas.

Age determination in the icefish Pseudochaenichthys georgianus (Channichthyidae) based on multiple methods using otoliths

Aging Antarctic icefish is difficult because of their lack of scales and poorly calcified bones. Icefish ages must therefore be estimated from otoliths. We describe a method of reading daily micro-increments in connection with shape, size and mass analyses of the otoliths of the South Georgia icefish Pseudochaenichthys georgianus. Changes in otolith morphology and mass correlate with fish size and age group. The otolith micro-increment analysis is capable of establishing the age of an icefish by relating the daily micro-increment count to the life history of the fish. Micro-increment measurements and analyses are relatively simple to do by light and scanning electron microscopy and by using micro-densitometer and digitizing equipment. Drastic changes in the life history of an individual are reflected by measurable changes in its otolith micro-increment data as seen in our analyses of age groups 0-VI. The initial drastic change in daily micro-increment shapes and periodicities occur in connection with the hatching period of the icefish. The next drastic change in otolith shape and daily micro-increments occurs when ~7 cm long fish shift from pelagic to benthic habitats. As the fish age beyond group III, individual otolith variability lessens until they begin spawning. Our results indicate a single population of P. georgianus between the Antarctic Peninsula and South Georgia.

Fish size effect on sagittal otolith outer shape variability in round goby Neogobius melanostomus (Pallas 1814).

Round goby Neogobius melanostomus (Pallas 1814) has become a significant component in the diet of piscivorous fish from the Pomeranian Bay (Bornholm Basin, Baltic Sea). Proper identification of fish species in the diet of predators is significant in biological studies of fish and other aquatic animal species, and, with regard to N. melanostomus, it is important to the knowledge of trophic web structures in areas this species has invaded. A total of 142 individuals of N. melanostomus, measuring 16-174 mm standard length, were examined. Seventy-two fishes were caught during monitoring surveys in fishing grounds, whereas 70 were found in the stomachs of European perch Perca fluviatilis, pike-perch Sander lucioperca and Baltic cod Gadus morhua. The objective of the present study was to analyse the sagittal otoliths to identify variations in outer shape with increases in fish length; expand and correct descriptions of the sagitta, lapillus and asteriscus otoliths; and evaluate the relationships among otolith dimensions and fish standard length. The otoliths were described morphologically. The analysis of the outer shape of sagittal otoliths using Fourier analysis and multivariate statistics exhibited great phenotypic variability that was associated with fish length, including within pairs in individuals and/or among individuals in length classes. In addition, the asterisci and lapilli of N. melanostomus from selected specimens, which were described for the first time with regard to fish length, were found to be less variable compared to sagittal otoliths. This study presents the first analysis of intrapopulation phenotypic plasticity of N. melanostomus sagittal otolith morphology as it is linked to fish size.

Comparative otolith morphology of clupeids from the Iranian brackish and marine resources (Teleostei: Clupeiformes)

AbstractThe diagnostic features of otolith morphology were provided for the clupeid fishes of the Iranian brackish and marine resources to be used as diagnostic features for the identification of clupeids diversity in these regions. Fish individuals belong to 20 species belong to 13 genera, and four families were collected from the Caspian Sea, the Persian Gulf and the Makran zone of the Oman Sea. Overall, seven otolith morphotypes were distinguished, that is lanceolated (45%), fusiform (20%), boot‐like (15%) and clamp‐like, pentagonal, elliptic and rectangular (each 5%, respectively). The univariate analysis showed that all variables except shape index [sulcus area (SS)/otolith area (OS)] and ROx (roundness) were significantly different among the clupeid species. The interspecific relationships of the otoliths were analysed based on the data of otolith morphology and otolith shape indices. Both dendrograms showed somehow an obvious separation among the studied species. However, the interspecific relationships in the dendrogram based on the otolith morphology have a better resolution. These phenotypic relationships based on otolith morphology among the studied clupeids are largely consistent with the previous hypothesis on the systematics of these fishes and emphasized that the morphological and morphometric features of the otolith, which are highlighted in this study, could be adequately used as diagnostic features for the identification of clupeids diversity.

Comparative analysis of otolith morphology in icefishes (Channichthyidae) applying different statistical classification methods

The genus Chionodraco includes three morphologically similar species, two of them (C. hamatus and C. myersi) living sympatrically in the Eastern Antarctica, and the third one (C. rastrospinosus) being distributed in the Western Antarctica along the southern Scotia Arc. The few overlapping diagnostic characters are often useless for the right taxonomic identification of three species, complicated by the presence of hybrids between them. In the present study, we tested the discrimination power of sagittal otolith shape as a tool to distinguish among these closely related species. An array of shape indices and elliptic Fourier descriptors were individually obtained from sagittal otoliths and analysed using three different models for species classification: Linear Discriminant Analysis (LDA), Random Forest (RF) and K-nearest neighbour (KNN). According to the characteristics of the adopted metric (precision), none of the methods resulted to be the absolute best approach as the performance largely varied with the species. The overall precision was 63 %, 66 % and 70 % for LDA, RF and KNN respectively, so that KNN can be considered the best classifier model. As expected, C. myersi was the best recognized species by all classifier models, consistently with its morphological and phylogenetic difference from the other two species. Taking into account the observed pattern of otolith morphology of the three species and their own geographical distribution, we were able to evaluate the role of genetic, endogenous or environmental components in influencing otolith size and shape.

Morphometric analysis of anchovy (Engraulis encrasicolus Linnaeus, 1758) otoliths in Georgia and Marmara Seas

The objective of the study was to examine whether there is a geographical differentiation between the anchovy stocks as well as to carry out otolith morphology and shape analyses work on the otoliths of anchovies caught in Georgia and Marmara. Otoliths obtained from anchovies (Engraulis encrasicolus) caught at two different regions (Georgia and Marmara Sea) were used for otolith morphology and shape analysis in the fishing season of 2011-2012. LAS Image Analysis 3.8 software in MZ75 Leica imaging system was used for biometric measurements and shape analyses of the otoliths. The average lengths of the otoliths were measured to be 2.94±0.263 mm for Georgia anchovy and 2.74±0.123 mm for Marmara anchovy. Additionally, the average widths of the otoliths were measured to be 1.44±0.142 mm and 1.31±0.579 mm for anchovy from Georgia and Marmara, respectively. The shape factor in the otolith shape analyses was measured to be 0.49≤FF≤0.74 for the Georgia anchovy and 0.55≤FF≤0.70 for the Marmara anchovy. The roundness factor for Georgia anchovy was determined to be 1.26≤RD≤1.97 and for the Marmara anchovy it was 1.33≤RD≤1.69. The length/width ratio was determined to be 1.81≤AR≤2.28 for Georgia anchovy and between 1.90≤AR≤2.37 for Marmara anchovy. According to the statistical analyses carried out in the two regions. AR and FF values were calculated to be statistically significant (p<0.05).

Intrapopulation variation of otolith associated with ontogeny and morphological dimorphism in Hormuz tooth‐carp Aphanius hormuzensis (Teleostei: Aphaniidae)

AbstractThe intrapopulation variation in otolith morphology was investigated for the first time in a recently discovered tooth‐carp Aphanius hormuzensis by considering ontogenetic variation and morphological dimorphism. The otolith materials were examined by scanning electron microscopy and quantitative analyses. The results underlined clear ontogenetic variation in the otolith morphology, which could be valuable to delineate the certain developmental stages of A. hormuzensis. Besides, some otolith features were found to be consistent during fish development and, therefore, appreciated to identify the species. The otoliths of A. hormuzensis demonstrated considerable sexual dimorphism in the adult fishes. Also, morphological side dimorphism was observed more in the otoliths of the females. As a result, the present study designated a clear intrapopulation variation in the otolith of A. hormuzensis, which were mainly influenced by fish development, sexual factors and morphological side dimorphism. The outcomes of the present study provide new basic data on the natural intrapopulation variation of this tooth‐carp during its life history and offered new data to interpret those factors that regulate otolith shape during the development, which has less been considered in previous studies.

Comparative otolith morphology and species identification of clupeids from Japan

The amount of interspecific and ontogenetic variation in otolith shape among clupeid fishes from Japan was investigated to create a key to identify otoliths of these species found in the stomach contents of piscivorous predators, fossiliferous beds, and archaeological sites. The interspecific comparison with 12 species (Clupea pallasii, Etrumeus micropus, Herklotsichthys quadrimaculatus, Ilisha elongata, Konosirus punctatus, Nematalosa come, Nematalosa japonica, Sardinella aurita, Sardinella melanura, Sardinella zunasi, Sardinops melanostictus, and Spratelloides gracilis) revealed morphological variation in otolith shape, OL:OH and AL:RL ratios, rostrum, marginal structures, and features of the crista superior. Intraspecific changes were analyzed in two species (E. micropus and S. melanostictus), revealing ontogenetic changes in OL:OH ratio and consequently otolith shape as well as changes in marginal features. Overall, this study shows that the key morphological features can be used as diagnostic features for identification of clupeid otoliths.