Otolith Morphometry Research Articles

Age, growth and otolith morphometry of Atlantic bonito (Sarda sarda Block, 1793) from the eastern Mediterranean Sea

The otoliths of the Atlantic bonito, Sarda sarda (Bloch, 1793), were examined with the aim to estimate the age and growth of the species in the eastern Mediterranean Sea and to reveal possible relationships between otolith shape or size and age. All specimens used in this study, ranging from 7.2 to 70.4 cm in fork length and from 20 to 4889 g in total weight, were caught in the Aegean and Ionian Seas during the period 1997-2010. Otolith morphometry was studied using image analysis techniques for all intact sagittae ranging in weight from 0.6 to 11.3 mg and four shape indices were calculated. No statistical significant differences between left and right otolith morphometric variables were found. The age of fish was estimated by counting the pairs of opaque and translucent bands in transversal thin sections of otoliths. The estimated ages ranged from 0+ to 7 years and the von Bertalanffy growth parameters were determined \((L∞=79.9 cm, k=0.261 and to=-1.230 years)\). The examination of the type of growth bands at the outside margin of each otolith per month showed that one translucent band is formed annually during the cold season. The results revealed statistically significant relationships between otolith morphometric variables and fish length or age. Among the variables, otolith weight was the one that showed the highest correlation with age (R=0.77). Therefore, otolith weight could represent a valuable criterion for age estimation in Atlantic bonito that is objective, economic and easy to perform compared to annuli counting method in hard parts.

Using otolith morphometry for the identification of three sympatric and morphologically similar species of Astyanax from the Atlantic Rain Forest (Argentina)

In several genera, the otolith shape is species-specific and the use of this structure provides a useful tool aiding in the species identification. In many studies regarding Neotropical fish fauna, species of the genus Astyanax are commonly identified at the genus level, mainly due to the phenotypic plasticity of the morphological characters traditionally used for species determination. In consequence, additional tools intended to better elucidate the taxonomic boundaries between species of Astyanax are certainly needed. In the last decade, the shape of otoliths has allowed to discriminate among closely related species. In this work, Fourier descriptors and shape indices of lapillus otolith were evaluated for the discrimination among three sympatric species of genus Astyanax inhabiting streams of the Atlantic Rain Forest (Argentina). Aspect ratio, roundness and ellipticity of otoliths were significantly different between the species (p 0.05). PERMANOVA analysis reveal significant differences between species using Fourier descriptors (F = 96.7, 0.0001 < p < 0.02) and the reclassification rates of quadratic discriminant analysis were high, averaging 86.3% (82.7 - 88.6%). Multivariate analyses of shape indices were not effective to discriminate between species. Instead, high classification percentages suggest that the otolith outline is a potential tool for the identification of sympatric morphologically similar species of Astyanax. Our results could contribute to future taxonomic and phylogenetic studies and may be an interesting input for both paleontological and trophic studies in sympatric species.

What can goby otolith morphology tell us

The taxonomic information inscribed in otoliths has been widely ignored in ichthyological research, especially in descriptions of new fish species. One reason for this is that otolith descriptions are per se qualitative, and only a few studies have presented quantitative data that can support assignments of otoliths to individual species or permit differentiation between higher taxonomic levels. On the other hand, in palaeontology, otoliths have been employed for the identification and taxonomic placement of fossil fish species for over 100 years. However, palaeontological otolith data is generally regarded with suspicion by ichthyologists. This is unfortunate because, in the Cenozoic, the fossil otolith record is much richer than that based on skeletons. Thus fossil otoliths are a unique source of information to advance our understanding of the origin, biogeographical history and diversification of the Teleostei. This case study deals with otoliths of the Oxudercidae, which, together with the Gobiidae, encompasses the 5-branchiostegal-rayed gobiiforms. The objective was to determine whether the five lineages of the Oxudercidae, and individual species of the European Pomatoschistus lineage, could be distinguished based on the quantification of otolith variations. The data set comprises otoliths from a total of 84 specimens belonging to 20 recent species, which represent all five lineages of the Oxudercidae (Mugilogobius, Acanthogobius, Pomatoschistus, Stenogobius, Periophthalmus), and five fossil otoliths of dagger Pomatoschistus sp. (sensu Brzobohaty, 1994). Ten measurements were taken on each otolith and 23 otolith variables were computed and used for univariate and multivariate analyses. The results indicate that otolith morphometry (i) is capable of identifying the Pomatoschistus and Periophthalmus lineages among the Oxudercidae, but is of limited use in the separation of the other three lineages;(ii) can reliably distinguish the sand gobies (a distinct Glade within the Pomatoschistus lineage) from other members of the Pomatoschistus lineage;and (iii) supports a previous assignment of fossil otoliths to dagger Pomatoschistus sp. as an ancient genus of the sand gobies. With its middle Miocene age (15 m.y. ago), dagger Pomatoschistus sp. represents the oldest record of a sand goby species to date. We discuss possible relationships between distinct otolith morphologies, biogeographic distribution and lifestyles for Pomatoschistus and the Periophthalmus lineage, and also for the sand gobies. We conclude that otolith morphology, combined with morphometry, can be considered as an autapomorphy for an individual species from the studied groups. In addition, it also appears to contain a phylogenetic signal, but more work is needed to evaluate this fully.

Relationship between somatic growth and otolith growth: a case study of the ornate jobfish Pristipomoides argyrogrammicus from the coast of Réunion (SW Indian Ocean)

The ornate jobfish Pristipomoides argyrogrammicus Valenciennes 1832 occurs in the Indo-West Pacific Ocean, where it is harvested by small-scale coastal fisheries. Management of this species is hindered by lack of adequate biological data. We sampled a total of 113 individuals from the landings of local artisanal fishers on the island of Réunion (southwestern Indian Ocean), from March 2014 to March 2015. The relationships between two types of body length (total and standard length, cm) and total weight (g) were shown to be significant (p < 0.05). The length–weight relationship was described by a power function, with the scaling factor estimated to be 0.008 and the exponent 3.146. Age was determined using whole otoliths. The von Bertalanffy growth equation was estimated to be TLt = 30.68(1 – e−0.52(t)). Otolith morphometry variables (length, width and area) were significantly correlated with age estimates (p < 0.05). No significant difference in age estimates was observed between left and right otoliths used as predictors. Readings from observed age and the estimates from modelled age indicated relatively good agreement, suggesting the potential to use whole otoliths for age estimation.

Spatial distribution, total length frequencies and otolith morphometry as tools to analyse the effects of a flash flood on populations of roach (Rutilus rutilus)

AbstractFloods are known to be the major source of natural variability and disturbance in stream ecosystems. However, the management and channelisation of large rivers have impacted the fluvial geomorphology and disconnected the main channel and floodplains used as nurseries by many species of fish. This study examines the influence of a first autumnal flood event of the Ardèche River on the roach population, Rutilus rutilus (Linnaeus, 1758), in the Caderousse reach on the Rhône River. This influence was evaluated through an analysis of the spatial distribution for the abundance and size of juvenile roach and an analysis of otolith shape. Juvenile roach from the three sections of the reach formed well‐defined local populations before and after the flood event. Juvenile roach were always more abundant in the less modified section (BPS) of the river than in the other sections (RES and TAIL). While the original primary river channel was directly impacted by the flash flood, no significant difference in otolith shape was observed before or after the flash flood. Our results suggest that this part of the reach provides refuge habitats used by fish during high flow events.

Morphometric analysis of otoliths of juvenile crucifix sea catfish Sciades proops (Valenciennes, 1840)

Summary The objective of this study was to analyze the morphometry of otoliths for Sciades proops juveniles by testing the hypothesis of equality in morphometric relationships for the right and left otoliths, which could then be interchangeably used to estimate fish size or weight. Samples were obtained monthly directly from anglers after each event that took place off the state of Sergipe from March/2014 to April/2015. Anglers used rod and reel during these events, with no restriction on hook size or line thickness. Each fish specimen sampled had their total weight (W, g) and total length (TL, cm) measured and their lapillus otoliths removed and stored separately. Each otolith had its length (OL), width (OWi), and thickness (OT) measured (all in mm) under a stereomicroscope. Otoliths were weighed using a precision scale (OW, g). A total of 883 specimens were sampled: TL = 12.0–60.5 cm and W = 9.8–1880 g. The weight-length relationship for the juvenile fishes was W = 0.0052TL3.086 and for their otoliths was OW = 0.0002OL3.177. The weight-length and length-length relationships fitted for each otolith (right and left) were not statistically different and thus all relations were estimated for grouped otoliths. The length-length relationships for the otoliths were: OWi = 0.947OL−0.205 and OT = O.484OL−0.698. The relationship estimated for juvenile fish and otolith weight was Wj = 1076.1OW−9.120. For juvenile fish total length and otolith length, width and thickness, the following relationships were estimated: TLj = 4.028OL−3.199, TLj = 4.208OWi−2.091, and TLj = 7.824OT + 3.659, respectively. Relationships between fish and otolith size, and between fish and otolith weight indicated a change in slope close to Lm50, which should be better explored when more adult specimens are available.

Otolith shape analysis as a tool for stock identification of the southern blue whiting, Micromesistius australis

The southern blue whiting, Micromesistius australis (Norman, 1937), is an important demersal resource associated with the slope and continental shelf of southern Chile, Argentina and the Malvinas/Falkland Islands. Recent studies have reported schools of adult fish from Atlantic waters migrating along the southern Chilean coast in mid-winter, moving northwards to spawn in August (47º-51ºS), and then returning to Atlantic waters, presumably to feed. The migratory pattern suggests the presence of one or more stock units associated with the South American coast. In the present study, “otolith morphometry” is used to determine the stock structure of M. australis based on applications of basic size descriptors (SDs) (area, perimeter and otolith size), shape indices (SIs) (circularity, squareness, shape factor, roundness, ellipticity), and normalised elliptical Fourier descriptors (NEFDs). Samples were collected during the winter and spring of 2010, during the reproductive period, in the economic zone of southern Chile (36º-57ºS), in the Pacific Ocean and around the Falkland Islands economic zone (50º-52ºS) in the Atlantic Ocean. Analyses were conducted to include the effects of size, sex and age. A stepwise canonical discriminant analysis showed that fish were successfully discriminated with SDs, SIs and NEFDs. In this analysis, 86.4% and 70.1% of the fish were correctly classified as belonging to the Atlantic and Pacific stocks, respectively. A multivariate analysis of variance showed that the mean values of the NEFDs, SDs, and SIs did not vary significantly between sexes within areas (P &gt; 0.05), but varied significantly between the Pacific and Atlantic oceans (P &lt; 0.05). These results highlighted that otolith shape analysis can be a useful tool to evaluate the potential level of mixing in feeding areas where both stocks, the Pacific and Atlantic units, are expected to co-occur.

Otolith morphometry and microchemistry as habitat markers for juvenileMugil cephalusLinnaeus 1758 in nursery grounds in the Valencian community, Spain

The aim of this study was to identify and characterize juvenile Mugil cephalus (flathead grey mullet) habitats in the Valencian community by means of otolith morphometry and microchemistry. Specimens (total length: 250–350 mm) were obtained from October 2011 to March 2012 with gill nets in two protected wetlands: the Parque Nartural de l'Albufera de Valencia (AV) (n = 45), a Mediterranean lake; and the Parque Natural Salinas de Santa Pola (SP) (n = 37), a coastal salt marsh. Otolith shape indices (circularity, rectangularity, aspect ratio, surface occupied by sulcus, ellipticity and form factor) and microchemistry (Sr/Ca and Ba/Ca ratios) were measured and compared as area markers. The chemical composition of the water in both areas was also obtained. Morphometric results showed, by an ANOVA with Bonferroni contrasts, that saccular otoliths from AV individuals had more edge complexity, hence a higher circularity index (p < .001), but that there was less otolith percentage occupied by the sulcus (p < .001). When analyzing the morphometric variables simultaneously, both sites differed significantly (Hotelling's T2 < 0.001). A paired t-test among sites of the microchemical variables showed that otoliths of AV presented higher values of Ba/Ca ratios and lower Sr/Ca ratios (p < .001). This coincides with water values obtained and could be associated with the low salinity observed in the lake. The opposite pattern was observed in SP, both for otolith and water samples, this being associated with the high-salinity waters of the area. Results obtained in the present research suggest, by the use of otolith morphometry and microchemistry, that the nursery grounds of juvenile M. cephalus in the Valencian community could be differentiated. Even though habitats could be separated using otolith morphometry, only a few of the studied shape indices were important in area differentiation. Nevertheless, the use of both methodologies simultaneously could be robust habitat markers for this species.

Otolith elemental fingerprint and scale and otolith morphometry in Prochilodus lineatus provide identification of natal nurseries

The dentification of nursery areas is a basic requirement for fishing management in large rivers. Morphometry (circularity, ellipticity, form factor, rectangularity and roundness indices) and chemistry (Sr:Ca, Ba:Ca and Zn:Ca ratios) of lapilli otolith, and geometric morphometry of scales of juveniles Prochilodus lineatus, were compared in three sites in the Plata Basin, in order to evaluate their applicability to identify possible nursery areas. Otolith microchemistry based on ICP-OES found significant differences in the Ba:Ca and Zn:Ca ratios among sampling sites. When all the combined techniques were considered, the quadratic discriminant analysis (QDFA) showed the highest classification success (89.5–92.9%), in relation to separate techniques classification. Otolith microchemistry, individually considered, appears to be a good and effective tool to identify individual fish from different locations (77.8%–84.2%). Otolith morphometry found significant differences in the ellipticity, circularity and form factor indices between sites. Otolith morphological indices supported results from the elemental study with a success in the allocation of 63.2–78.6%. When considering all variables for scale geometric morphometry, discriminant analysis showed a good percentage of the classification of the individuals (58.3–82.8%). These results indicate that the otolith microchemisty and morphometry and scale morphometry are acceptable markers of habitat and represent a potential tool (in combination or individually) for the identification of streaked prochilod nursery areas.

Identification of nurseries areas of juvenile Prochilodus lineatus (Valenciennes, 1836) (Characiformes: Prochilodontidae) by scale and otolith morphometry and microchemistry

ABSTRACT The streaked prochilod Prochilodus lineatus (Valenciennes) is a commercially freshwater species from South America, distributed in the Plata basin. In the present work the morphometry (circularity, rectangularity, form factor, OL/OW and ellipticity indices) and chemistry (Sr:Ca, Ba:Ca, Zn:Ca) of lapilli otolith, and geometric morphometry of scales of streaked prochilod juveniles, in two sites in the Plata basin (Uruguay River and Estrella Wetland), were compared to determine if they are area-specific and to identify possible breeding areas. Otolith Ba:Ca ratios was 0.017±0.003 mmol/mol for Uruguay River while for Estrella Wetland individuals was bellow the detection limits. Zn:Ca ratios tended to be higher for the latter (0.03±0.002 mmol/mol). Significantly high circularity and low rectangularity values were obtained for Estrella Wetland otoliths (p &lt; 0.05), while no significant differences for form factor, OL/OW and ellipticity were observed between sampling sites. Considering all scale geometric morphometry variables, discriminant analysis showed a good percentage of classification of individuals (90.5% for Estrella Wetland and 85.7 % for Uruguay River). These results indicate that the otolith microchemisty and morphometry (circularity and rectangularity indices) and scale morphometry are good markers of habitat and represent a potential tool for identification of streaked prochilod nursery areas.

Ontogenetic development of the sagittal otolith of the anchovy, &lt;em&gt;Anchoa tricolor&lt;/em&gt;, in a subtropical estuary

In order to characterize the ontogeny of Anchoa tricolor , the morphology and morphometry of sagitta otoliths were described. A total of 397 pairs of sagitta otoliths of A. tricolor (20 to 85 mm) were measured and analysed by means of digital images. Morphological description was done in terms of shape and features. The Huxley model was fitted to otolith length against total length (TL) and weight (TW), and residual analyses were done in order to detect the polyphasic growth. Six shape indices were calculated (otolith height/otolith length and otolith length/total length aspect ratios, rectangularity, roundness, relative sulcus surface and rostrum index) and after size effect removal, they were analysed in terms of TL. The results of these analyses allowed three distinct growth phases to be identified: (1) up to 40 mm TL and related to low swimming ability; (2) between 41 and 60-70 mm TL, when fish displacements increase but the first maturation has not yet occurred; and (3) after 71 mm TL, when fish become adults. Landmarks and semi-landmarks were used to analyse relative warps during the otolith development. The MANOVA analysis between the centroid size and class intervals showed significant differences in the interaction of all classes except between 71-80 and 81-90 mm.

Otolith Sr:Ca ratio and morphometry as indicators of habitat of a euryhaline species: The case of the silverside Odontesthes bonariensis

The silverside Odontesthes bonariensis is a euryhaline species native of South America and represents a very important fishing resource for the Plata Basin (Argentina and Uruguay). This study compares the Sr:Ca ratio of water as well as the Sr:Ca ratio and morphometry of the sagittal otolith of the silverside present in different environments (one salt lake, two freshwater dams, one lagoon, and one estuary) in order to evaluate the use of these variables as markers of habitat. The pattern of the Sr:Ca ratio in the water agrees with the one found in the otoliths, showing a positive relationship with the conductivity of the water. Univariate and multivariate analyses of variance indicated significant differences (P &lt; 0.05) among the localities studied for the morphometric indices. The discriminant function analysis provided a high percentage of correctly classified individuals for the saltwater environment (100%) and the lentic water bodies and estuary (60–80%), circularity and form factor being the most relevant morphometric variables. These results indicate that the Sr:Ca ratio and otolith morphometry are good markers of habitat for this important resource.

Assessment of the morphometry of saccular otoliths as a tool to identify triplefin species (Tripterygiidae)

In the present work we describe nine saccular otolith morphometric indices (circularity, rectangularity, aspect ratio, percentage of the otolith surface occupied by the sulcus, percentage of the sulcus length occupied by the cauda length and ostium length, otolith length relative to the length of the fish, rostrum aspect ratio and percentage of the rostrum length occupied by the otolith length) of 41 species of the Tripterygiidae family collected mainly from New Zealand, Australia, Chile, South Africa, Mediterranean Sea and North America. The principal component of analysis showed that the indices that best explain the variability between species were related to sulcus and rostrum morphometry. According to cluster analysis, otolith morphometry could reflect the diversity of microenvironments for some genera such asNotoclinopsandForsterygion, while this does not happen to genera likeEnneapterygiusandRuanoho. The discriminant analysis showed that the speciesHelcogrammoides cunninghami, Karalepis stewarti, Lepidoblennius haplodactylus, Notoclinus compressus, Ucla xenogrammuscan be discriminated by using the morphometric indices. Two new indices related to the sulcus that were of great value for the discrimination of these species are described for the first time. This information will be a useful tool for palaeontological, taxonomic and trophic ecology studies.

Morphometry and relative growth of the Brazilian sardine, Sardinella brasiliensis (Steindachner, 1879) in the southeastern Brazilian bight

The Brazilian sardine, Sardinella brasiliensis, is small pelagic clupeid fish distributed primarily between 22°S and 29°S, where it forms large schools. The species is an important fishery resource and is targeted by purse seine vessels operating in the area. Although an extensive literature addresses various characteristics of the species, studies of its morphometry and relative growth are scarce. The aim of the present study was to analyze the relative growth based on body and otolith morphometry to identify the patterns characterizing the population. Monthly samples were obtained during 1985 and 1987, and data on total length, total weight and otolith length, height and weight were analyzed. The allometric model of Huxley (y = ax ) was fitted seasonally and by year, and regressions were compared among seasons and between years. The regression coefficient b was tested (t-test) to identify isometry and allometry. A total of 603 sardines, with total lengths ranging from 120 mm to 229 mm, were analyzed. The length-weight relationships tended to show positive allometry, whereas the total length-otolith measurement relationships tended to show negative allometry. The relative growth rates decreased during the year and showed the lowest values during spring in association with the peak of the spawning period. In contrast, the condition factor (coefficient a of the allometric regression) increased gradually during the year until spring as consequence of the increasing weight of the fish due to gonad maturation. Comparisons between the years analyzed also show that the fish grew faster during the collapse of the stock, in 1987. The methodology used in this study allowed the detection of this effect. This study established the historical pattern of relative growth and showed that morphometry and relative growth offer efficient tools for monitoring the sardine in the study area.

Otoliths of five extant species of the annual killifish Nothobranchius from the East African savannah.

This study presents, for the first time, a comprehensive dataset that documents the range of inter- and intraspecific otolith variation in aplocheiloid killifish, based on a total of 86 individuals representing five extant species of Nothobranchius PETERS, 1868, from East Africa: the sympatric pairs N. rubripinnis SEEGERS, 1986 and N. ruudwildekampi COSTA, 2009 (Eastern Tanzania), and N. orthonotus (PETERS, 1844) and N. furzeri JUBB, 1971 (Southern Mozambique), and two isolated populations of N. korthausae MEINKEN, 1973 (Eastern Tanzania). Otolith characters were analysed based on SEM images, and otolith morphometry was conducted using uni- and multivariate statistics. Two ancient clades of probably Early to Middle Miocene age in eastern Tanzania and southern Mozambique can be recognized based on otolith morphologies, which is consistent with previous work based on molecular data. The distinctive sulcus morphologies in the otoliths of sympatric species may be linked to species-specific hearing capabilities, perhaps constituting a case of character displacement in an area of secondary sympatry. The otoliths of the studied species of Nothobranchius are diagnostic at the species level, even in the case of closely related species diagnosable otherwise only by minor differences in coloration. The two populations of N. korthausae also displayed some differences in their otolith characters. The new data may facilitate future recognition of fossil species of Nothobranchius. As no fossil remains of extant aplocheiloid killifishes have yet been described, the discovery of fossil otoliths of Nothobranchius would significantly advance understanding of the evolutionary history of this interesting group of fishes.

&lt;b&gt;Lapillus otoliths of the &lt;i&gt;Cathorops spixii&lt;/i&gt; (Spix &amp; Agassiz, 1829) and &lt;i&gt;Genidens genidens&lt;/i&gt; (Cuvier, 1829) (Actinopterygii - Ariidae)

The aim of this study was to analyze the morphology and morphometry of lapillus otoliths of the catfishes Cathorops spixii and Genidens genidens from the coast of Parana State, Brazil. We used 147 lapillus from C. spixii and 96 from G. genidens, of different size classes. Otoliths were characterized with smooth margins for both species but with different shapes: oblong for C. spixii and oval for G. genidens. The morphological differentiation between the two species is in the anterior region: rounded for C. spixii and pointed for G. genidens. The t-test results for otolith measurements were: length (t value = -2.88; p = 0.0042), height (t value = -6.87; p < 0.000001), anterior angle (t value= 9.84; p = 0.000001) and posterior angle (t value =0.41; p = 0.68). The results show that lapillus otoliths of C. spixii and G. genidens differ in the shape of the anterior region and in the anterior angle, which facilitate the differentiation between the two species in trophic ecology studies on ichthyophagous.

Rapid and reliable multivariate discrimination for two cryptic Eteline snappers using otolith morphometry

Previously unaccounted cryptic speciation requires revaluating species identification, particularly for fisheries assessment purposes. We describe a rapid and reliable method for distinguishing between phenotypically similar species that utilizes simple otolith morphometry (length, width, thickness and weight) with or without fish length, within a traditional canonical discriminant analysis (CDA). Data were subject to CDA in order to differentiate between the cryptic Etelis carbunculus (ruby snapper) and E. marshi (pygmy ruby snapper). A very high allocation success rate was achieved using otolith morphometry and fork length (99.6% for E. carbunculus and 100% for E. marshi) or otolith morphometry only (98.8% for E. carbunculus and 100% for E. marshi), which indicated the high discriminatory power of this method. The CDA successfully grouped samples of the same species collected from different locations in the eastern central Indian and South Pacific Oceans, indicating the robustness of this technique to discriminate between species, irrespective of their geographic range. This technique can be applied to archived otolith collections to confirm teleost species identification, and likely has broader applications for species identification involving extractive, diet or video-based studies.

Combined use of otolith microchemistry and morphometry as indicators of the habitat of the silverside (Odontesthes bonariensis) in a freshwater–estuarine environment

The silverside Odontesthes bonariensis is a highly salt-tolerant freshwater–estuarine species found in the Southern Hemisphere. The objective of the present study was to perform a simultaneous evaluation of the morphometry and microchemistry (Sr/Ca and Ba/Ca ratios) of the otoliths of this species to provide information on its displacements and to identify fish stocks. The morphometry and microchemistry of fish otoliths from three regions of the lower section of the Plata Basin (Uruguay River, Paraná River Delta and De la Plata River estuary) were compared. The results showed that otoliths of fish from the southern lower section of the Plata Basin tended to be circular in shape and had a lower ratio of sulcus perimeter to total otolith perimeter than those fish collected in the north of the studied region. There is a trend to increase the otolith Sr/Ca ratio with increasing water conductivity along a latitudinal (north–south) gradient, while the Ba/Ca ratio decreased significantly along such gradient. Present results suggest that the silverside population may be geographically divided along the north–south axis of the lower section of the Plata Basin.

On the intraspecific variation in morphometry and shape of sagittal otoliths of common sardine, &lt;i&gt;Strangomera bentincki&lt;/i&gt;, off central-southern Chile

Size and shape of fish otoliths are species-specific, but some species also display intraspecific variations. The common sardine, Strangomera bentincki , is a small pelagic fish inhabiting a seasonal upwelling ecosystem off central-southern Chile, having two discrete spawning sites along its latitudinal distribution. Otoliths of specimens were collected from commercial catches in Talcahuano and Corral, representing the central and south spawning zones. On the basis of otolith images, size-based shape descriptors were used to detect ontogenetic variation, and morphometric variables (length, breadth, area, perimeter and weight) were used to detect geographical differences in size and shape of otoliths. Outline analysis was studied on the basis of elliptic Fourier descriptors through multivariate statistical procedures. Size-based shape descriptors showed that otolith shape starts to be stable for fish larger than 12 cm total length, which keep an elliptical form. Morphometric variables for fish larger than 12 cm revealed intraspecific variation between central and south zones, which were associated with otolith weight and breadth. Outline analysis did not reveal significant spatial differences, but extreme intraspecific variation was due to the antirostrum, excisure , and posterior part of otoliths. Intraspecific variation in otolith size could be linked to differences in each spawning habitat and related to geographical origin, whose differences are not clearly identified. It is concluded that intraspecific variability in morphometric variables of sardine otoliths revealed geographic differences in size that are not attributable to allometric effects, and that otolith shape was similar between specimens from different geographic origin.

Growth pattern of the young of the year Argentine hake Merluccius hubbsi Marini, 1933 (Gadiformes Merluccidae) along the Brazilian and Uruguayan coasts

Morphology and morphometry of the sagittae otolith were studied in young of the year Argentine hake, Merluccius hubbsi in the Southeastern Atlantic. Geographical variation in the growth pattern of the young of the year Merluccius hubbsi was correlated with the differences found in otolith morphometry, relative growth, ring positions, as well as the formation of a new ring. The otolith development of M. hubbsi throughout its area of distribution accompanies an increasing northward temperature gradient, resulting in bigger otoliths and greater variability of ring position from northern to southern area. The canonical discriminate analysis showed that the otolith length and height explained most of the variation of the first discriminant function. We found significant differences in the discriminant scores between those samples from northern and southern area. As regards the Uruguayan coast and Southern Brazil, age groups zero shared some similarity as well as differences in growth; environmental features explain these differences but their effect on the adult fishes growth is still unknown.