Climbing for dummies: recommendation for multi‐specific fishways for the conservation of tropical eels and gobies

Dams and other man-made barriers impair upstream fish migration and thus threaten fish populations that need access to upper river reaches to complete their life cycle. For many years, fishways have been used to mitigate this impact. Fishways around the globe are typically built based on recommendations made for northern hemisphere species, particularly salmonids. These recommendations do not consider the locomotor characteristics and skills of other species, especially those living in the tropics. Among tropical species, freshwater eels and gobies of the Sicydiinae subfamily are important cultural and economic species that are particularly sensitive to the impact of man-made barriers. Our experimental study aimed to test different substrates and slopes for ramp-like fishways adapted to tropical eels and sicydiines. Among the five substrates tested for 368 eels Anguilla marmorata, elastomer pins appeared to be the most efficient. Elastomer pins also appeared to be more efficient than the fine concrete which is currently used in fishways for sicydiines (Sicyopterus lagocephalus, N = 1797, and Cotylopus acutipinnis, N = 1303). The slope had a lesser effect on the climbing success of sicydiines compared to substrate type, except for gradients greater than 50° that induced a slight decrease in success. Our results indicated that ramp-like fishways fitted with 1.0 cm diameter elastomer pins, positioned in staggered rows with a diagonal spacing of 1.3 cm, wetted with low-flow and angled less than 50°, are well adapted to accommodate the different locomotor characteristics and skills of tropical eels and sicydiines

The GRAVITY+ Project: Towards All-sky, Faint-Science, High-Contrast Near-Infrared Interferometry at the VLTI

The GRAVITY instrument has been revolutionary for near-infrared interferometry by pushing sensitivity and precision to previously unknown limits. With the upgrade of GRAVITY and the Very Large Telescope Interferometer (VLTI) in GRAVITY+, these limits will be pushed even further, with vastly improved sky coverage, as well as faint-science and high-contrast capabilities. This upgrade includes the implementation of wide-field off-axis fringe-tracking, new adaptive optics systems on all Unit Telescopes, and laser guide stars in an upgraded facility. GRAVITY+ will open up the sky to the measurement of black hole masses across cosmic time in hundreds of active galactic nuclei, use the faint stars in the Galactic centre to probe General Relativity, and enable the characterisation of dozens of young exoplanets to study their formation, bearing the promise of another scientific revolution to come at the VLTI.Comment: Published in the ESO Messenge

Mieux comprendre les composantes des résistances à l'hyperthermie et à l'hypoxie aiguës chez la truite arc-en-ciel, à des fins de sélection

Climate change is leading to an increase in the frequency and intensity of hyperthermic and hypoxic events in aquaculture farms. This leads to stunted growth, increased susceptibility to diseases and higher mortality. Rainbow trout, the main fish species farmed in France, is a coldwater fish that is particularly sensitive to water quality, including temperature and oxygen availability. Genetic selection for resistance to acute hyperthermia and hypoxia is a promising solution for reducing the vulnerability of trout farms to climate change. However, knowledge of the genetic determinism of these resistances is still too fragmented to envisage optimized selection. Moreover, resistance phenotyping protocols are still very global, and procedures are classified as severe by French ethics committees. A more detailed understanding of the phenotypes of resistance to acute hyperthermia and hypoxia would enable a better understanding of the underlying mechanisms, and the development of indirect criteria whose measurement procedures would be less stressful. Genetic architectures of resistance to acute hyperthermia and hypoxia were studied separately in French commercial populations of rainbow trout. Estimates of genetic parameters of resistance traits and genetic correlations with key production traits demonstrate the feasibility of genetic improvement of resistance traits. Genetic determinism of resistance traits is clearly polygenic, but several functional candidate genes were identified. Further studies, using six isogenic lines characterized for their resistance to acute hyperthermia or hypoxia, showed that these resistances seem to be globally stable traits with fish age, and that genetic links between resistance to acute hyperthermia and resistance to acute hypoxia are tenuous. The same six isogenic lines were phenotyped for behavioral and physiological parameters before or after moderate hyperthermic stress. Their activity levels were positively correlated with resistance to acute hyperthermia, and negatively correlated with resistance to acute hypoxia. Lines resistant to acute hyperthermia seem to have a different energy allocation strategy compared to sensitive lines during temperature increase. These results open up new possibilities for understanding the mechanisms underlying resistance traits.Le changement climatique a pour conséquence une augmentation en fréquence et en intensité des pics hyperthermiques et hypoxiques dans les fermes aquacoles. Cela induit retard de croissance, susceptibilité accrue aux maladies et hausse de la mortalité. La truite arc-en-ciel, principale espèce piscicole élevée en France, est un poisson d'eau froide et oxygénée, particulièrement sensible à la qualité d'eau. La sélection génétique des résistances à l'hyperthermie et à l'hypoxie aiguës est une solution prometteuse pour réduire la vulnérabilité des fermes trutticoles au changement climatique. Cependant les connaissances sur le déterminisme génétique de ces résistances sont encore trop parcellaires pour envisager une sélection optimisée de celles-ci. De plus, les protocoles de phénotypage des résistances sont encore très globaux et sont des procédures classées sévères par les comités d'éthique français. Une compréhension plus fine des phénotypes de résistances à l'hyperthermie et l'hypoxie aiguës permettrait de mieux comprendre les mécanismes sous-jacents et le développement de critères de sélection indirects dont les procédures de mesure seraient moins sévères. Les architectures génétiques des résistances à l'hyperthermie et à l'hypoxie aiguës ont été étudiées séparément sur des populations commerciales de truite arc-en-ciel françaises. Les estimations des paramètres génétiques des résistances et des corrélations génétiques avec les principaux caractères de production démontrent la faisabilité de l'amélioration génétique des résistances. Le déterminisme génétique des résistances est clairement polygénique mais plusieurs gènes candidats fonctionnels ont été identifiés. Des études supplémentaires, à l'aide de six lignées isogéniques caractérisées pour leurs résistances à l'hyperthermie et à l'hypoxie aiguës, ont permis de montrer que les résistances semblent être des phénotypes globalement stables avec l'âge des poissons et que les liens génétiques entre résistance à l'hyperthermie aiguë et résistance à l'hypoxie aiguë sont ténus. Les six mêmes lignées isogéniques ont été phénotypées pour des paramètres comportementaux et physiologiques avant ou après un stress hyperthermique modéré. Leur niveau d'activité est lié positivement avec la résistance à l'hyperthermie aiguë et négativement avec la résistance à l'hypoxie aiguë. Les lignées résistantes à l'hyperthermie aiguë semblent avoir une stratégie d'allocation de l'énergie différente de celle des lignées sensibles lors d'une montée en température. Ces résultats permettent d'envisager de nouvelles pistes de compréhension des mécanismes sous-jacents aux résistances et le développement de critères indirects de sélection

Influence of environmental conditions on the distribution of burrows of the mud crab, Scylla serrata, in a fringing mangrove ecosystem

International audienc

Influence of environmental conditions on the distribution of burrows of the mud crab, Scylla serrata, in a fringing mangrove ecosystem

International audienc

Temporal variability of larval drift of tropical amphidromous gobies along a watershed in Réunion Island

International audienceFreshwater gobies of tropical islands are amphidromous: adults reproduce in rivers and larvae passively drift down to the sea immediately after hatching. Describing the phenology of this larval drift is essential to understanding the population dynamics of amphidromous gobies and to developing ecologically based recommendations for managing the watersheds. The larval drift patterns of two amphidromous gobies of Réunion Island, Sicyopterus lagocephalus and Cotylopus acutipinnis, were studied on a monthly basis for 1 year using plankton nets at two sites on the Mât River, located 20 km and 7 km from the river mouth. Genetic analyses showed that larval assemblages were dominated at 90% by S. lagocephalus, although the proportion of C. acutipinnis increased during early summer. Our findings highlighted a marked larval drift peak in full austral summer. The diel larval drift dynamic was described using periodic linear models. A diel pattern was only observed downstream, peaking a few hours after sunset. Finally, this study presents a new approach that improves standard methods for sampling and analyzing larval drift of amphidromous species

Influence of larval and juvenile life history on age at first maturity in two tropical amphidromous fish species

International audienceThis study investigates how age at first maturity of two tropical amphidromous spe‐cies Sicyopterus lagocephalus (Pallas, 1770) and Cotylopus acutipinnis (Guichenot, 1863) varies in relation to their larval and juvenile life history. Reproductive stage was estimated based on histological observation of ovaries of more than 200 females of each species caught monthly over 1 year. The age of fish was estimated by interpret‐ing the daily increments deposited on otoliths during the oceanic larval phase, and the juvenile phase in the river. The age at first maturity was approximately 9 months for S. lagocephalus and 7 months for C. acutipinnis, corresponding to approximately 70–130 and 90–130 days after they returned to freshwater respectively. For both species, the time spent in freshwater before maturity was significantly influenced by the duration of the pelagic larval stage at sea (PLD) and the season of return in freshwater. Individuals with a long PLD, or returning in freshwater during the warmer season, maturated faster once in freshwater. This reproductive advantage may mini‐mise the risk of extirpation due to catastrophic events at each generation and thus probably benefits amphidromous species living in very unpredictable tropical rivers

Internal tides responsible for lithogenic inputs along the Iberian continental slope

This study details the sediment resuspension due to internal tides (ITs) and the afterward propagation of suspended particles along and off the Iberian continental slope. Five resuspension sites are precisely identified along the western Iberian shelf slope using a tidal regional model of Bay of Biscay and Iberian continental shelf. Two sites are sources of lithogenic material only, one of biogenic matter only and two are sources of a mixture of both. The potential pathways for particles from the resuspension sites toward the GEOVIDE stations are identified using the IBIRYS reanalysis to infer their transport by the ocean circulation. It appears that each station is influenced by a specific pathway and mixed particles from different resuspension sites. This methodology enables to establish more realistic interpretations of the geochemical in situ observations combining distinct modeling of ITs and oceanic circulation as well as in situ sediment properties. It also reveals that the criticality of the bathymetry slope, commonly used to trigger the potential occurrence of ITs, is not sufficient to investigate their role in sediment resuspension. An explicit resolution of the ITs using a numerical tidal model is required to identify more exhaustively all the actual resuspension sites

Optical and spin coherence of excitons in zinc-blende GaN

The carrier recombination processes and the relaxation dynamics of spin-polarized excitons in cubic epitaxial GaN have been investigated by time-resolved photoluminescence and pump-probe spectroscopy experiments. We evidence a very fast exciton spin relaxation tau(S)similar to 0.3 ps that is influenced by both the high defect concentration and the strong electron-hole exchange interaction. Spectral oscillatory features of the transient reflectivity are observed for negative delays that allow us to determine the exciton optical dephasing time T-2