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Les pièces calcifiées ont des origines ontogéniques et des propriétés différentes. C’est pourquoi, dans le but d’évaluer les utilisations potentielles des otolithes, des écailles et des tissus squelettiques pour les études de sclérochronologie, il est important de bien comprendre la nature et la formation des accroissements dans ces différentes structures. Dans ce chapitre, nous décrirons la fonction, la morphologie et la structure des différentes pièces calcifiées. Puis, nous ferons une revu...

Les chapitres précédents ont montré que les écailles, les otolithes et les os du squelette sont utilisés pour estimer l’âge des poissons en année, en saison ou en jour. La préparation des pc nécessite une série d’étapes de traitement qui peuvent être longues et complexes. Préalablement au démarrage d’une étude de sclérochronologie, il est nécessaire d’identifier les contraintes en termes de temps et de coûts et surtout les objectifs finaux et les résultats attendus (chap. III). Le choix d’une...

Il est impossible de connaître l’âge absolu, « âge véritable », d’un poisson prélevé au hasard dans son environnement naturel. De nombreuses analyses de pêcheries dépendent cependant d’estimations exactes et fiables des structures en âge des captures. La constatation de nombreuses erreurs dans les estimations d’âge a relancé l’intérêt des méthodes de validation. « Valider » signifie qu’il faut prouver qu’une technique est exacte. Ceci peut être démontré ou estimé. Une estimation a bien sûr mo...

Contrairement aux idées reçues, la sclérochronologie, en particulier l’estimation de l’âge chez les poissons, n’est pas une science aisée. Elle implique une série de processus et de traitements de données qui sont souvent complexes et consommateurs de temps. Avant même de commencer de telles études, il est nécessaire de connaître à l’avance les contraintes sur le temps disponible et sur les coûts et, particulièrement, les objectifs de l’étude ainsi que les résultats attendus. Ce chapitre va a...

Gurnards are demersal fishes exploited by commercial trawl fisheries that spend a pelagic phase during their early life history stages. There are eight different species in the Mediterranean showing intra- and inter-specific differences related to feeding habits, depth distribution and biological cycle. Although these changes have been widely reported little is known about their first life stages due to a lack of information on age and size at settlement to the bottom, length at first year of age and otolith formation. The present study is the first attempt to determine the first growth stages of six gurnard species: Chelidonichthys cuculus, C. lucerna, Eutrigla gurnardus, Lepidotrigla cavillone, L. dieuzeidei and Trigloporus lastoviza and to determine the first annuli formation. Indirect validation is made by counting presumed daily increments on two defined radii: the first radius is measured along the proximal-distal axis from the primordium to the last increment before the apparition of an accessory growth centre (AGC); the second radius is measured from the more dorsal AGC to the proximal edge of the otolith close to the sulcus acusticus and perpendicular to the increment deposition. The duration of the pelagic life phase was determined and the first annulus was defined by the position of one year-increment count in terms of distance from primordium and annulus density (i.e., translucent vs. opaque). The location of discontinuous and incremental zones linked to developmental changes, the description of the species-specific patterns, as well as the measurement of increment widths are discussed in the light of the species ecology and biology.

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[EN] The larval growth and development of the European hake, Merluccius merluccius, was studied from field larvae. Larvae were collected in the northwestern Mediterranean on three cruises carried out during the peak spawning months (November 1998, September 1999 and November 1999). Like other species of the genus, these larvae are characterised by a well-developed anterior part of the body, head and trunk region. Nevertheless, yolk sac larvae are much more slender than larvae at notochordal flexion stages. In the present study we analysed the allometric relationships between several body measurements and body length. This is the first attempt to infer larval growth of Merluccius merluccius by means of sagittal otolith analysis. Our results show the change in the otolith shape from a lenticular otolith in early larvae to an almond-shaped otolith in larger larvae. Otolith diameter showed a power relation with larval size, with no significant differences between seasons. In spite of the sea surface temperature differences between the three periods of larval collection, the early growth estimates showed no significant differences. This was explained by the similarity in the temperature at the depths at which the larvae are located. Absolute growth rates in length were estimated by relating daily growth increments in otoliths and larval size (standard length). When using the whole larval size range the values obtained were similar to those found for other Merluccius species. Nevertheless, the present data evidenced that growth for larvae younger than 12 days is very low, showing a significant increase thereafter. This indicates that length is probably not the best parameter for describing the growth of hake larvae in the first days of life, as allometric analysis suggested [ES] Se estudió el crecimiento y desarrollo larvario de la merluza europea, Merluccius merluccius, a partir de larvas capturadas en el mar. Las larvas se pescaron en el Mediterráneo noroccidental en tres campañas que se realizaron durante los meses de máxima puesta (Noviembre 1998, Septiembre 1999 y Noviembre 1999). Como otras especies del mismo género, estas larvas se caracterizan por tener la parte anterior del cuerpo, la cabeza y el tronco, bien desarrollada. Sin embargo, las larvas lecitotróficas son mucho más alargadas que las larvas en estado de flexión del notocordio. En este estudio, analizamos las relaciones alométricas entre algunas medidas del cuerpo y la longitud del mismo. Es la primera vez que se realiza un estudio del crecimiento larvario de Merluccius merluccius por medio del análisis de los otolitos sagitta. Nuestros resultados muestran que hay un cambio en la forma del otolito, pasando de forma lenticular en larvas pequeñas a forma almendrada en larvas de mayor tamaño. El diámetro del otolito se relaciona con la talla de la larva mediante un ajuste potencial, sin encontrarse diferencias significativas en las distintas épocas analizadas. A pesar de las diferencias en la temperatura superficial encontradas en los distintos periodos muestreados, no hubo diferencias significativas en las estimas de crecimiento larvario de las tres campañas. Esto se explicaba por la similitud de las temperaturas en las profuncidades en que las larvas de merluza se distribuyen. Se estimaron tasas absolutas de crecimiento en talla relacionado el número de incrementos de crecimiento diario de los otolitos y la longitud estándar. Cuando se usó todo el rango de talla de las larvas se obtuvieron valores muy similares a los de otras especias de Merluccius. Sin embargo, nuestros datos evidenciaron que el crecimiento de las larvas de menos de 12 días de edad es muy bajo y aumenta significativamente en los días posteriores. Esto indica que probablemente la longitud no es el mejor parámetro para describir el crecimiento de la merluza en los primeros días de vida, tal como se sugería con el estudio de alometrías This study was funded by grants under the following research programmes: 'Fil' Spanish CYTMAR MAR 97 09-02, and 'Llucet' EU Contract FAIR CT-97-3522 (1998-2000)

Young-of-the-year European hake (Merluccius merluccius) were sampled during four seasonal cruises between November 1998 and September 1999. The greatest numbers and biomass were found in spring 1999. Some 73% of juvenile fish in terms of number, and 81% in terms of biomass, were caught at depths between 60 and 160 m on the outer western Mediterranean shelf, where the water temperature ranged between 13.5 and 14°C. The length composition of samples showed there to be small hake all year around, with modes between 7 and 11 cm total length depending on the season. Otolith analysis was used to establish age at settlement (62.7 days) and to determine seasonal growth. The monthly growth rates ranged from 1.2 cm month-1 for juvenile hake captured on February 1999 to 2.5 cm month-1 for ones captured in June. The growth rates are related to survival, as was shown by the calculated hatch dates and relative abundances of recruits. This work provides information on the first year of life, recruitment and growth processes in an important species of the Mediterranean demersal ecosystem which is heavily exploited by a recruitment fishery., Juveniles de la merluza europea fueron muestreados durante cuatro cruceros estacionales realizados entre 1998 y 1999, la mayor biomasa se encontró en la primera de 1999 y entre 60 y 160 m. de profundidad. Las tasas de crecimiento están relacionadas con la supervivencia. Este trabajo provee por primera vez información sobre el primer año de vida.

The sagittal otoliths of Lates niloticus, Haplochromis obesus, and Oreochromis niloticus from Lake Victoria were examined for daily growth rings using scanning electron microscopy. In the three species the increments were clear and thick enough to allow future studies with light microscopy. The daily nature of the increments seems supported by the rhythmic growth that were found.

La sclérochronologie, discipline qui étudie les pièces calcifiées pour reconstruire l'histoire individuelle des organismes vivants, est essentielle pour la connaissance de la biologie des poissons et la gestion des pêches. Ce manuel présente une synthèse actualisée sur les aspects théoriques et pratiques des études de sclérochronologie. En donnant des informations sur la nature des pièces calcifiées (otolithe, écaille, squelette), leur utilisation dans les recherches en ichtyologie et les méthodes de préparation et d'observation, ce manuel constitue un guide détaille pour les chercheurs, techniciens et étudiants novices ou désirant étendre leurs domaines d'expertise. Sclerochronology, the study of calcified structures tore-construct the past history of living organisms, is central to fish biology and fisheries management. This manual aims to provide an overview of the current theoretical and practical aspects of sclerochronological studies. By providing information on the nature of calcified structures (otoliths, scales, skeleton), their uses in fish research and methods for preparation and examination, the manual constitutes a comprehensive guide for researchers, technicians and students either new to the field or interested in expanding their range of expertise.