Algunas consideraciones sobre la acuicultura

El crecimiento de la acuicultura en las últimas décadas en España y en el mundo, ha convertido esta actividad en el sector de la producción primaria de más rápido crecimiento. Sin embargo este crecimiento ha ido acompañado de una considerable evolución en los mercados y de importantes cambios que han sido dirigidos fundamentalmente a la mejora del producto y al aumento de la diversidad de especies, para ofrecer al consumidor un alimento de confianza, variado y sano desde el punto de vista económico, nutricional y sanitario. Esto también ha llevado a la regulación de zonas consideradas protegidas en algunos casos, o de dominio público en otros, para su utilización en acuicultura de forma racional. De la misma manera, no podemos olvidar el papel fundamental que esa desarrollando la acuicultura en los países en vías de desarrollo, como un elemento indispensable para erradicar el hambre, ni los efectos drásticos que pueda tener el cambio climático en el futuro de la acuiculturaDuring the last decades, aquaculture has become the activity with the fastest growth in the primary sector in Spain. Nevertheless, this growth has been accompanied by a remarkable evolution of the market and important changes towards mainly to the improvement of quality product and species diversification, in order to deliver a trust worthy, healthy, nutritional and reliable product for the consumer. This has also contributed to new regulations, regarding protected areas in some cases, or of public domain in others, allowing their utilization in aquaculture in a rational and responsible manner. Furthermore, we can not forget the important role that aquaculture has in developing countries, as a vital element to eradicate hunger, nor the drastic effect that climate change could have in the future of aquaculture

Individual spawning control in different turbot (Scophthalmus maximus L.) broodstock under artificial and natural photoperiod

As fry output depends highly on management and control of the spawners, this paper examines the results with spawn obtained under a natural and artificial light cycle over a one-year period. The broodstock consisted of 55 females and 69 males, distributed with the same age and sex ratio in 5 tanks. Two of tanks were subjected to controlled photoperiod (group A) and the other three to natural conditions (group B). The spawning period of group A lasted from March until June, and that of group B from May to October. During this period, the spawning sequences of females were monitored individually. The total production of larvae was 2,233,254 larvae, of which 71.72 % were from the tanks with controlled photoperiod. In the fifth tank, fema1es which had not spawned in the previous years were tested, and no 1arvae were produced. This confirmed that the criterion for se1ection was adequate. A mean of 260,933 eggs per Kg of females were obtained, of which 45.56% were of good qua1ity. The mean ferti1ization and hatching indices were 71.40% for group A and 21.99% for group B (not inc1uding tank T-5).0,000

Effect of light and temperature on the development of turbot eggs

Different experiments were done to determine the effeets of light and temperature on the embryonie development of turbot eggs (Seophthalmus maximus L.) obtained in eaptivity. No signifieant differen~es have from fertilization to hC'tehing in the been found between time elapsed trials earried out wi th 24 hours of light and those done in dark eonditions,therefore light is not a determining faetor in the embryonie development of turbot eggs. The relation between temperature and time needed to reaeh eaeh embryonie stage, shows a elear inverse relationship. The exponential-potential equation whieh relates temperature and the age of the eggs, defined as the time in hours elapsed sinee fertilization, is: Y = 27.64 . e -0.11 T + 0.05 i . 1.21 1 r = 0.9904 paper also provides for eaeh experimental From the applieation of this equation, this th~ development eurves for eaeh embryonie stage temperature (in the range 10 QC to 20 QC)

Crossover in the nature of the metallic phases in the perovskite-type RNiO_3

We have measured the photoemission spectra of Nd$_{1-x}$Sm$_{x}$NiO$_{3}$, where the metal-insulator transition and the N\'{e}el ordering occur at the same temperature for $x \lesssim 0.4$ and the metal-insulator transition temperature ($T_{MI}$) is higher than the N\'{e}el temperature for $x \gtrsim 0.4$. For $x \le 0.4$, the spectral intensity at the Fermi level is high in the metallic phase above $T_{MI}$ and gradually decreases with cooling in the insulating phase below $T_{MI}$ while for $x > 0.4$ it shows a pseudogap-like behavior above $T_{MI}$ and further diminishes below $T_{MI}$. The results clearly establish that there is a sharp change in the nature of the electronic correlations in the middle ($x \sim 0.4$) of the metallic phase of the $R$NiO$_3$ system.Comment: 4 pages, 4 figure, submitted to Phys. Rev.

Inducción y sincronización de la puesta en el rodaballo (Scophthalmus maximus) con LHRHa: influencia del estado de desarrollo gonadal

Female turbot in different stages of gonadal maturation (initial, average or advanced) were injected i.m. with 5¡dkg PV of LHRHa. A limited response was detected in the initial gonadal maturation group, whereas induced spawning was experienced by 100% of average and advanced females, with a high level of synchronization. The number of ovulatory cycles was low, eggs quality variable and egg production high. New works are neccesary to improve the performance of this technique.Hembras de rodaballo en distintos estados de maduración gonadal (inicial, medio o avanzado) recibieron una inyección i.m. de 51L1Kg PV de LHRHa. La respuesta ha sido escasa o nula en hembras en desarrollo gonadal inicial, mientras que se ha inducido la puesta con un alto nivel de sincronización en el 100% de las hembras en estado medio o avanzado. El número de ciclos ovulatorios ha sido bajo, la calidad de las puestas variable y el volumen de huevos elevado. Se consideran necesarios nuevos trabajos al objeto de optimizar el rendimiento de esta técnica de control de reproducción

Effect of band-filling and structural distortions on the Curie temperature of Fe-Mo double perovkites

By means of high resolution neutron powder diffraction at low temperature we have characterized the structural details of $\rm La_{x}Sr_{2-x}FeMoO_6$ ($0\leq {\rm x}\leq 0.5$) and $\rm Ca_{x}Sr_{2-x}FeMoO_6$ ($0\leq {\rm x}\leq 0.6$) series of compounds. This study reveals a similar variation of the mean bond-angle \FeOMo in both series. In contrast, the mean bond-distance \FeMoO\ increases with La but not with Ca substitution. Both series also present a different evolution of the Curie temperature ($T_C$), which raises in the La series and slightly decreases in the Ca one. We thus conclude that the enhancement of $T_C$ in the La series is due to the electron filling of the conduction band and a concomitant rising of the density of states at the Fermi level.Comment: Revtex, 4 Journal pages, 2 figures, 1 tabl