Biological characteristics of sperm in European flat oyster (Ostrea edulis)

In brooding mollusc species that incubate larvae before their release in seawater, the biology of gametes remains poorly explored. The present study describes some biological characteristics of sperm of the European flat oyster, a native species that has been over-exploited in the past and is nowadays classified as an endangered species in Europe. Flat oysters were collected by divers in the Rade de Brest (Finistère, France), during its natural reproduction period. Gonadal pH is acidic (6.31 ± 0.10). Spermatozoa are clustered in spermatozeugmata, an acellular structure in which the sperm heads are embedded. After their transfer in seawater, spermatozeugmata have a mean diameter of 64 ± 3 μm and they release free spermatozoa for a mean duration of 21 ± 3 min. Immediately after their release, the mean percentage of motile spermatozoa was 48.5 ± 12.6%. At 10 min after dilution in seawater, movement of spermatozoa was no more observed. Biological characteristics of European flat oyster sperm are compared to those observed in the Pacific oyster, regarding the unique reproductive behaviour of the former species and the role of spermatozoa transfer played by spermatozeugmata. The present results aim to improve the knowledge of reproduction and natural recruitment processes, support conservation and restoration measures and favour the establishment of management protocols of gametes and larvae in this endangered species

Effective elastic properties of 3D stochastic bicontinuous composites

We study effective elastic properties of 3D bicontinuous random composites (such as, e.g., nanoporous gold filled with polymer) considering linear and infinitesimal elasticity and using asymptotic homogenization along with the finite element method. For the generation of the microstructures, a leveled-wave model based on the works of J. W. Cahn [J.W. Cahn. Phase separation by spinodal decomposition in isotropic systems. The Journal of Chemical Physics, 42(1):93-99, 1965.] and Soyarslan et al. [C. Soyarslan, S. Bargmann, M. Pradas, and J. Weissmüller. 3D stochastic bicontinuous microstructures: generation, topology and elasticity. Acta Materialia, 149: 326-340, 2018.] is used. The influences of volume element size, phase contrast, relative volume fraction of phases and applied boundary conditions on computed apparent elastic moduli are investigated. The nanocomposite behaves distinctly different than its nanoporous counterpart without any filling as determined by scrutinized macroscopic responses of gold-epoxy nanocomposites of various phase volume fractions. This is due to the fact that, in the space-filling nanocomposite the force transmission is possible in all directions whereas in the nanoporous gold the load is transmitted along ligaments, which hinges upon the phase topology through network connectivity. As a consequence, we observe a distinct elastic scaling law for bicontinuous metal-polymer composites. A comparison of our findings with the Hashin-Shtrikman, the three-point Beran-Molyneux and the Milton-Phan-Tien analytical bounds for the same composites show that computational homogenization using periodic boundary conditions is justified to be the only tool in accurate and efficient determination of the effective properties of 3D bicontinuous random composites with high contrast and volume fraction bias towards the weaker phase

Le lieu jaune (Pollachius pollachius) : biologie, pêche, marché et potentiel aquacole

This work reviews data available in the literature on pollack. This species is only observed in N-E Atlantic and in the Channel. Pollack spawns in spring. From a size of 5 cm, juveniles move into deeper water. The growth is rapid. From 1979, fishing has been stabilized around 10 to 15.000 tonnes. In 1996, France was the first producer of pollack. However, this production decreased from 1989, as in many other European countries. Between 1995 and 1998, the wholesale selling price ranges from 16.6 F/kg to 20.0 F/kg. The main sources of variation are the period, the location and the selling year. The retail price is comprised between 40 F/kg and 110 F/kg, depending on the presentation and the distribution channel. Rearing attempts are rare and limited to France. Large quantities of eggs were collected in captivity. Hatching rate remained low. First larval rearing attempts were encouraging. However, weaning remained difficult. When temperature was comprised between 13 and 18°C, a mean weight of 400 g was reached 18 months after hatching. The best growth was recorded at 16°C. However, good results were observed between 12 and 18°C. The assets of pollack for aquaculture are numerous: a rapid growth at water temperature close to those recorded on the Atlantic coast of France, a first sexual maturity recorded only in fish weighing more than 1 kg, a good quality flesh, the availably of juveniles and breeders in the wild, the encouraging results recorded in rearing attempts and a fillet yield similar to those of farmed fish species. However, the wholesale selling price is low. For aquaculture purpose, the production cost of pollack has to be lowered. For comparison with pollack, some data concerning saithe are included in this work. Because of its very low selling price, this species is not a good candidate for aquaculture.Ce travail fait le point des données disponibles dans la littérature sur le lieu jaune. L’espèce n est observée que dans l'Atlantique nord-est et dans la Manche. Le lieu jaune pond au printemps. A partir d’une taille de 5 cm, les juvéniles gagnent des eaux profondes. La croissance est rapide. La pêche mondiale s’est stabilisée depuis 1979 à des valeurs comprises entre 10 et 15.000 tonnes par an. En 1996, la France était le premier producteur de lieu. Mais cette production décroît depuis 1989, comme dans de nombreux pays européens. Entre 1995 et 1998, le prix de vente du lieu jaune en criée est compris entre 16,6F/kg et 20,0 F/kg. Les sources essentielles de variation du prix sont la période, le lieu et enfin l’année de vente. Au détail, les prix sont plus élevés et compris entre 40 F/kg et 110 F/kg selon la présentation et le circuit de commercialisation. Les essais d’aquaculture sont rares et restent cantonnés à la France. Des quantités importantes d’œufs ont été récoltées en captivité. Le taux d’éclosion reste faible. Les premiers essais d’élevage larvaire sont encourageants, bien que le sevrage semble délicat. A une température comprise entre 13 et 18°C, un poids moyen de 400g est atteint 18 mois après l’éclosion. Bien que la meilleure croissance soit observée à 16°C, de bons résultats sont enregistrés entre 12 et 18°C. Les atouts du lieu jaune pour l’aquaculture sont nombreux: croissance rapide à des températures proches de celles relevées sur les côtes atlantiques françaises, première maturité sexuelle n’apparaissant que vers 1 kg, chair de bonne qualité, disponibilité en juvéniles et reproducteurs, premiers résultats enregistrés en élevage encourageants, rendement à la découpe comparable à celui relevé chez d’autres espèces d’aquaculture. Le prix de vente en crié est cependant faible. Le prix de revient en élevage devra donc être bas pour que le lieu jaune s’avère être un bon candidat à l’élevage. Quelques données concernant le lieu noir sont rajoutées à ce travail, permettant une comparaison avec le lieu jaune. En raison de son très faible prix de vente, le lieu noir n’est pas actuellement un bon candidat à l’élevage

Sexual dimorphism of drumming muscles in European hake (Merluccius merluccius)

Dissections of mature and non-mature European hake males and females (N = 142) collected in waters off the western coast of Norway and in the Bay of Biscay (France) in 2004–2006 demonstrate for the first time that this gadoid species contains drumming muscles. There were differences in drumming muscles weight with body length, sex and maturity stage. This study shows that the difference between females and males is primarily manifested during the spawning season, seen both in the French and Norwegian samples. For the mature females the drumming muscles dry weight increases only slightly, if at all, with increase in total length. For mature males there is a corresponding rapid increase. There does not seem to be any consistent difference between the average dry weight of the drumming muscles in immature male and immature and mature female hake of the same length, tested on the Norwegian samples. Our results suggest that male hake, like the males of other gadoids studied, may produce sounds in the context of spawning

La domestication des poissons : le cas du thon rouge

Bluefin tuna shows adaptative physiology features allowing life in a wide range of physical and climatic parameters like temperature, salinity and hydrostatic pressure, hence the species fulfil the main basic requirements for progressive domestication and rearing in captivity. The high mortalities recorded after handling and the losses observed after abrupt variations of environment in the cages, emphasised the extreme sensitivity to stress of tuna. As consequences, the progresses about the control of tuna biological cycle are very slow due to limited handling possibilities and tuna aquaculture is restricted to fattening of wild fish. At this time, bluefin tuna production progresses without domestication of the species.Le thon rouge présente des caractères adaptatifs lui permettant de vivre dans une gamme large de paramètres physiques et climatiques tels que la température, la salinité et la pression hydrostatique. L’élevage de l’espèce et une domestication progressive pouvaient donc être envisagés. Les mortalités importantes observées après manipulation et les pertes liées aux variations brutales de l’environnement en cage ont révélé l’extrême sensibilité du thon au stress. Cette nouvelle caractéristique de ce poisson pélagique diminue les possibilités d’intervention humaine durant l’élevage. Celui-ci se limite à l’engraissement d’individus sauvages et les progrès sur le contrôle du cycle biologique de l’espèce sont extrêmement lents. On peut dire que la production de thon progresse sans domestication de l’espèce

Evaluation of fish sperm quality

P>The development of cheaper technical tools and the availability of well established assay kits provide today the spermatologists with several devices for objective and quantifying assessment of sperm quality. The present paper reviews modern methods on sperm concentration assessment, morphometry, motility processes through flagellum studies, motility objective assessment by computer assisted sperm analysis (CASA), sperm integrity and energetic state measurements