Sulcus Acusticus Research Articles

Different sagitta otolith morphotypes for the whitemouth croaker Micropogonias furnieri in the Southwestern Atlantic coast

Otoliths are part of the auditory system of teleostean fishes, and are species-specific structures that may have intraspecific variation depending on the environmental conditions at a regional scale. The main aim of this study was to assess changes in otolith shape of Micropogonias furnieri along its geographical distribution range between the tropical and warm temperate coastal of Southwestern Atlantic. Ten otoliths from each of six areas along the South American coast were examined:1) Rio de Janeiro State (23°S); 2) São Paulo State (24°S); 3) Santa Catarina State (27°S), 4) Rio Grande do Sul State (32°S); 5) Uruguayan coast (35°S); 6) Northern coast of Argentine (39°S). The sagitta otolith contour and shape were characterized using the Elliptical Fourier Analysis (EFA) and the morphometric measurements of both otoliths and respective sulcus acusticus were performed using the software ImageJ. Variations of otolith shape were assessed by five explanatory variables (area, perimeter, width, circularity and the maximum Feret diameter) and a Principal Components Analysis (PCA) was applied to Elliptical Fourier Descriptors. We found significant differences in area, perimeter and circularity of otoliths. Clustering the range of the 30 first harmonics using Ward’s hierarchical algorithm yielded three otolith morphotypes. Plots of the two first Principal Component (PCs) axes for the 60 examined otoliths did not discriminate the population distribution along the six areas. The three different otolith morphotypes do not seem to be subjected to a clinal variation for this transition area in the Southwestern Atlantic, and suggest an overlap of individuals of different stocks/populations mixing along their geographical distribution range favored by their eurythermic and euryhaline characteristics.

Morphology study of the otoliths of the parrotfish,Chlorurus sordidus(Forsskål, 1775) andHipposcarus harid(Forsskål, 1775) from the Red Sea coast of Egypt (Family: Scaridae)

In the present study a comparison of the otolith morphology of two species of parrotfish, family Scaridae, collected from the Red Sea coast of Egypt, is conducted to identify the most appropriate taxonomic characters that separate these species. Ontogenetic changes in the otoliths of the two scarid fishes become evident. In the otoliths ofChlorurus sordidus, the following characters are comparable in small-sized adult fishes: otolith width, otolith depth, mesial surface shape, lateral surface shape, shape of sulcus acusticus, column, rostrum and size of rostrum. The otoliths of young adults (GI)C. sordidusdiffer from the adult ones in 14 out of the 22 characteristics studied. In the otoliths ofHipposcarus harid, the following characters are comparable in small and large fish: otolith width, otolith depth, mesial and lateral surface shapes, shape of sulcus acusticus, rostrum and size of rostrum.

Testing otolith morphology for measuring marine fish biodiversity

To check the suitability of otoliths for measuring biodiversity, the contour and shape of the sulcus acusticus of sagittal otoliths were described using geometric morphological analysis. Thirteen and fourteen points were used to define these structures respectively. Three current coastal fish assemblages of the north-western Mediterranean were selected for the present study. The results demonstrate that the relative warps generated in the geometric analysis explained both characteristics related to contour and the otolith sulcus. A comparative study with body fish shape using morphospaces and clusters revealed that otolith shape is a better variable for explaining the ecological structure of a fish assemblage. Moreover, three morphological indices (morphological richness (MR), morphological disparity and the morphogeometric index) were estimated from relative warps of otoliths and were compared with ecological, taxonomic, functional and morphological (from body shape) indices. MR increased with functional diversity and average taxonomic distinctness, reflecting the ecological and taxonomic character of otolith morphology. These findings suggest that otoliths could be a useful tool for studying the diversity of present and past fish assemblages.

Spatial Expression of Otolith Matrix Protein-1 and Otolin-1 in Normally and Kinetotically Swimming Fish.

Kinetosis (motion sickness) has been repeatedly shown to affect some fish of a given clutch following the transition from 1g to microgravity or from hypergravity to 1g. This susceptibility to kinetosis may be correlated with irregular inner ear otolith growth. Otoliths are mainly composed of calcium carbonate and matrix proteins, which play an important role in the process of otolith mineralization. Here, we examine the morphology of otoliths and the expression pattern of the major otolith proteins OMP-1 and otolin-1 in a series of hypergravity experiments. In the utricle, OMP-1 is present in centripetal (medial) and centrifugal (lateral) regions of the meshwork area. In the saccule, OMP-1 was expressed within a dorsal and a ventral narrow band of the meshwork area opposite to the periphery of the sulcus acusticus. In normal animals, the spatial expression pattern of OMP-1 reaches more posteriorly in the centrifugal aspect and is considerably broader in the centripetal portion of the utricle compared to kinetotic animals. However, otolin-1 was not expressed in the utricule. In the saccule, no differences were observed for either gene when comparing normal and kinetotically behaving fish. The difference in the utricular OMP-1 expression pattern between normally and kinetotically swimming fish indicates a different otolith morphology and thus a different geometry of the otoliths resting on the corresponding sensory maculae. As the utricle is the endorgan responsible for sensing gravity, the aberrant morphology of the utricular otoliths, based on OMP-1 expression, likely leads to the observed kinetotic behavior.

Intra-specific and inter-specific variability of the sulcus acusticus of sagittal otoliths in two gurnard species (Scorpaeniformes, Triglidae)

Morphology, morphometries and compounds of sulcus acusticus of sagittal otoliths of two gurnard species (Aspitrigla cuculus and Eutrigla gurnardus) from north-central Adriatic Sea (north-eastern Mediterranean) were investigated. The study objectives were to find morphometric variables and shape variability of sulcus acusticus of these two closely related sound producers species linked to developmental changes from juvenile to adult stage and species-specific pattern which influenced ecomorphological adaptations of the auditory system. The method used was a combination of multivariate techniques, X-ray diffractions pattern and ultrastructural investigation by SEM. Multivariate analysis (PCA, LDA and PERMANOVA) performed on standardized morphometrics of a total of 202 individuals, significantly separated four groups: A. cuculus juveniles, A. cuculus adults, E. gurnardus juveniles and E. gurnardus adults due to different life history characteristics. At intra-specific levels higher mean values of sulcus area/otoltih area (S:O) ratio of adults than the juveniles were observed within A. cuculus and not for E. gurnardus. At inter-specific levels significant differences were seen between adults and not between juvenile groups. Considering all the groups, the main variability on sulcus area were observed for caudal part of the sensorial macula. Although no differences in compounds were shown by X-ray diffraction at intra-specific level, the crystals on sulcus acusticus were different in shape, size and arrangement between juveniles and adults of each gurnard. The crystals of juveniles were quite enmeshed into otolith matrix and showed a rod/smooth-shape. The crystalline arrangement of adults became more complex with larger, rod/rectangular-shape and well-formed faces. Ontogenetic and specie-specific differences might be related to specie-specific physiological factor (i.e sexual maturity), depth distribution and feeding patterns that change during gurnards growth. These changes, relating to both endogenous and exogenous factors, were marked by the sulcus acusticus which provided a useful tool for fish ontogenetic, physiological and ecological studies.

An approach to unraveling the coexistence of snappers (Lutjanidae) using otolith morphology

Summary: The sagittae otolith morphology of marine fishes has been used in many ecomorphological studies to explain certain ecological adaptations of species to habitat. Our study compares the sagittal otolith shapes of ten species of snappers (Family Lutjanidae) inhabiting the Persian Gulf. We used a morphometric analysis of the otolith measurements (length, height, perimeter, area and weight) and of the ratio between the area of the sulcus acusticus and the area of the otolith (S:O). The otolith contour was also analysed using wavelets as a mathematical descriptor. Morphological variations in the otoliths were associated with the morphology and external colouration of snappers as well as ecological traits. An analysis of the interspecific S:O ratio suggested that the highest ratios occurred in snappers inhabiting shallower waters. A categorical multivariate analysis, including morphological, ecological and otolith size factors, showed that the species adapted to dim light conditions had a greater otolith perimeter. An analysis of variance of the otolith contour revealed zones with a higher interspecific variability, although only the antero-dorsal zone showed differing patterns. Although the otolith patterns appear to have a phylogenetic component, they might also be related to diel activity rhythms or to the light conditions in the habitat. The results of the study showed that variation in otolith morphology can be used to explain the coexistence of sympatric species.

Morphometry of the sagittal otolith from Atherinella brasiliensis (Quoy & Gaimard, 1824) (Actinopterygii - Atherinopsidae), at the coast of Paraná.

In this work was done the description of the morphological and morphometric of the otolith sagitta of the Atherinella brasiliensis together with the linear regressions between biometrics fish and otoliths. Were 145 specimens analyzed with total length of 7.01 cm and with a standard deviation of ± 4.28 cm. All sagitta otoliths of A. brasiliensis showed sulcus acusticus heterosulcoid shape and type ostial. With the growth of the specimens occurred changes in the shape and margins of the otoliths, in specimens having above 8 cm total length of the fish observed a dorsal depression. The appearance of this depression in the dorsal otolith this species is an indication of the stress caused by the first maturation of the species. Key words: Brazilian silverside, teleósteos and regression.

The morphology of saccular otoliths as a tool to identify different mugilid species from the Northeastern Atlantic and Mediterranean Sea

In the Northeastern Atlantic and Mediterranean Sea there are 8 species of the Mugilidae family: Mugil cephalus, Liza aurata, Liza ramada, Oedalechilus labeo, Chelon labrosus, Liza saliens, Liza carinata and Liza haematocheila. The identification of mugilids is very important for local fisheries management and regulations, but it is difficult using gross morphological characters. This work aims to contribute to the identification of mullets present in the Northeastern Atlantic Ocean and Mediterranean Sea using saccular otolith features of each species. Specimens of C. labrosus, L. aurata, L. ramada, L. saliens and M. cephalus were obtained from Delta del Ebro (40°38’N–0°44’E) in artisanal catches. For L. carinata and O. labeo photographs extracted from AFORO online database were used. L. haematocheila was not studied for lack of otolith samples. A general pattern of the saccular otoliths for this family was identified: the shape of the otoliths are rectangular to oblong with irregular margins; they present a heterosulcoid, ostial sulcus acusticus, with an open funnel-like ostium to the anterior margin and a closed, tubular cauda, ending towards the posterior ventral corner, always larger than the ostium. In the present study, the mugilid species could be recognized using their saccular otolith morphology. Here we give the first key to identify Northeastern Atlantic and Mediterranean mullets. The distinctive features between the species were the position and centrality of the sulcus, the curvature of the cauda, the presence of areal depositions and plateaus, and the type of anterior and posterior regions. These features could be used not only to reinforce the identification keys through morphological and meristic characters of the species, but also to identify the species consumed by piscivores, being the otoliths the only identifiable remains of the individuals.

Using sagittal otoliths and eye diameter for ecological characterization of deep-sea fish: <i>Aphanopus carbo</i> and <i>A. intermedius</i> from NE Atlantic waters

SUMMARY: The sagittal otolith and eye diameter of two sympatric species of the genus Aphanopus, A. carbo and A. intermedius, from North Atlantic waters were investigated. The study objectives were to find morphometric variables of otoliths to identify the two species and relate ecomorphological characters of otolith and eye diameter to the depth distribution of each species. The otoliths of the two species are very similar, although significant differences in shape, otolith height and weight and the sulcus acusticus area were detected. The ratio between eye diameter and cephalic length (ED:CL ratio) was also significantly different. In both analyses A. carbo obtained higher values, which suggests that A. carbo and A. intermedius live in different spatial niches, and that A. carbo inhabits deeper waters. The ratio between the sulcus and otolith areas (S:O) was low compared to other fish species, which suggests that the hearing capacity of Aphanopus spp. is adapted to low frequency sound. This adaptation may be related to the oceanographic conditions in which these species live, and in particular to the characteristics of sound transmission in the “SOFAR channel”.

Otolith atlas for the western Mediterranean, north and central eastern Atlantic

The sagittal otolith of 348 species, belonging to 99 families and 22 orders of marine Teleostean fishes from the north and central eastern Atlantic and western Mediterranean were described using morphological and morphometric characters. The morphological descriptions were based on the otolith shape, outline and sulcus acusticus features. The morphometric parameters determined were otolith length (OL, mm), height (OH, mm), perimeter (P; mm) and area (A; mm 2 ) and were expressed in terms of shape indices as circularity (P 2 /A), rectangularity (A/(OL×OH)), aspect ratio (OH/OL; %) and OL/fish size. The present Atlas provides information that complements the characterization of some ichthyologic taxa. In addition, it constitutes an important instrument for species identification using sagittal otoliths collected in fossiliferous layers, in archaeological sites or in feeding remains of bony fish predators.

Comparative morphology of the sagittal otolith in Serranus spp.

Variations in the morphology of saccular otoliths (sagittae) among three sympatric species of the genus Serranus(S. atricauda, S. cabrilla and S. scriba) from the Canary Islands were investigated. Although the otolith gross morphology was similar among species, S. scriba was distinct in having a rostrum which had a slight turning at the tip and a more funnel‐like ostium. The shallower water species (S. scriba) had otolith and sulcus areas which were smaller than the deeper water species (S. cabrilla and S. atricauda). The sulcus acusticus and ostium size were correlated with the habit depth of the species, with the highest values in the deepest species, S. cabrilla. The otolith outline shape indices changed with size (total length) of the species, and allowed the separation of the species by means of a discriminate function.

Variability of the sulcus acusticus in the sagittal otolith of the genus Merluccius (Merlucciidae)

The morphology of the sulcus acusticus of the sacular otolith (sagitta) was studied by means of image analysis on 12 extant species of the genus Merluccius. The digitization of the sulcus acusticus and the subsequent biometric analysis, by means of multivariate methods and the Fourier descriptors of the perimeters obtained, allowed the interspecific variability to be quantified. These results were in agreement with ecomorphologic (functional and environmental) and phylogenetic aspects. Analysis of the perimeters of the sulcus acusticus demonstrated a specific character and indicated the existence of two large groups: the American species and the Euro-African species, matching the phylogenetic lines. The principal difference between the two groups was found in the development of the caudal colliculum, which was relatively shorter in the American species. Within the Euro-African group, the deep-water species M. polli and M. paradoxus showed different characteristics with respect to the species from surface waters. Given the sensorial nature of the associated acoustic macula of the inner ear the sulcus is more likely to accurately reflect the species specific changes in otolith morphology.

Sagittal otolith size and shape variability to identify geographical intraspecific differences in three species of the genus Merluccius

A study was carried out on the morphology (size and shape) of the saccular otolith (sagitta) by means of image analysis on three species of the genus Merluccius (M. gayi, M. hubbsi and M. merluccius). By digitization of the sagittae, morphometry and outline (Fourier harmonic) as form descriptor measurements were obtained, that were subsequently analysed by means of multivariant methods, allowing the intraspecific variability to be quantified. The differences in the intraspecific sagittal otolith variability confirmed spatial differences of predicted groups. The results were associated with environmental and population aspects. The use of combined morphometric measurements for the whole otolith and its corresponding sulcus acusticus were very appropriate for determining the origin of the analysed otoliths. Using both principal components analysis and discriminant analyses, a clear geographical differentiation was obtained for Merluccius gayi (from Chile and Peru) and M. merluccius (from the Atlantic and Mediterranean). In both species, the discriminant analysis predicted that all the sagittae could be correctly assigned within each of the groups studied. However, it was a little less effective at differentiating between the two groups of M. hubbsi (from the San Matias Gulf on the Patagonian Shelf and Argentinian–Uruguayan Common Fishing Zone). As a result, the morphometric analysis of the sagittae otoliths acted as a clear diagnostic tool to differentiate individuals from different geographical distribution areas.

A morphological description of the sagittal otoliths of two mormyrids, Marcusenius macrolepidotus and Petrocephalus catostoma (Family: Mormyridae)

The morphology of the sagittal otoliths of two South African mormyrid fish, Marcusenius macrolepidotus and Petrocephalus catostoma, were studied to determine possible morphological significance. The sagittae of M. macrolepidotus and P. catostoma are kidney-shaped and oblong, respectively. The ventral margin is slightly indented in the former and slightly flattened in the latter. The sulcus acusticus of both species is archaesulcoid but mesial in M. macrolepidotus and ostio-caudal in P. catostoma. The crista inferior in M. macrolepidotus is ridge-like and well defined posteriorly and anteriorly, whereas in P. catostoma it is clearly defined posteriorly and disappears anteriorly. The otoliths of both species do not have a rostrum, antirostrum or an excisura. The differences in sagittal morphology between the two mormyrid species are distinct.

Ecomorphological comparisons of sagittae in Mullus barbatus and M. surmuletus

For both Mullus barbatus and M. surmuletus, the relationship between sagitta area (O), sulcus acusticus area (S) throughout postlarval growth was characterized by their negative allometric growth. The adjusted mean S: O ratio differed between the two species. This may be associated with the difference in size and shape of the sagittae, a difference in somatic growth, and differences in food and spatial niches. The inner ear of Mullus cannot be considered as specialized and the interaction of stimuli detected by the sensory barbels and the inner ear together could be a compensatory mechanism that helps in the food search.

Morphology and ultrastructure of saccular otoliths from five species of the genus Coelorinchus (Gadiformes: Macrouridae) from the Southeast Atlantic.

The morphology of the saccular otolith (sagitta) of five species of the genus Coelorinchus (grenadiers) from the southeastern Atlantic (C. coelorinchus, C. fasciatus, C. occa, C. braueri, and C. acanthiger) was analyzed macro- and ultrastructurally by digital image processing and scanning electron microscopy (SEM). Interspecies variations have been noted in the morphology and ultrastructure of the sulcus acusticus and are linked to differences in form of the entire otolith. This relationship may indicate a genetic regulation in the growth of the sulcus. Standard canonical analysis of biometric measurements of the otolith and acoustic sulcus has proved to be a good way to distinguish otoliths of the five species of Coelorinchus. © 1995 Wiley-Liss, Inc.

Changes in the ratio of the sulcus acusticus area to the sagitta area of Pomatoschistus minutus and P. lozanoi (Pisces, Gobiidae)

The Pomatoschistus minutus (Pallas) and P. lozanoi (de Buen) stock of the ebb-tidal delta of the former Grevelingen estuary was sampled monthly from September 1992 to October 1993. Sagittae were extracted and the areas of the sagitta and sulcus acusticus were measured with a digitizer. The frequency response and auditory threshold of these two sympatric goby species were determined from the ratio of the sulcus acusticus area to the sagitta area (S:O ratio). The S:O ratio of P. minutus increased while in P. lozanoi the S:O ratio was constant with increasing standard length. The average S:O ratio of P. lozanoi was significantly higher than that of P. minutus of the same mean length, which makes the former more sensitive to sound frequency. The S:O ratios of these two sympatric fishes were lower than the S:O ratios of demersal and pelagic fishes available from the literature. An interspecific growth difference of sagitta and sulcus acusticus was observed. The sagitta and sulcus acusticus of P. minutus are larger than those of P. lozanoi of the same length.

Changes in otolith area: sensory area ratio with body size and depth

The ratio between the sensory areas of the sulcus acusticus and the sagittal otolith (S : O ratio) in the species Merluccius capensis and M. paradoxus was analyzed using a digital image processing system. Sagittal growth in both species is negatively allometric with respect to total fish length but is more negative in the deeper-dwelling species, Merluccius paradoxus. In contrast, the sulcus acusticus undergoes a relative increase in size, that is, the S : O ratio increases with fish length. There was a clear relationship between the increase in the S : 0 ratio and depth.