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The present study tracked oocyte development over 9 months and noted incidences of ‘skipping’, i.e., adults terminating their upcoming reproductive cycle, in field-caught north-east Arctic (NEA) haddock (Melanogrammus aeglefinus), currently the largest stock of this species. Applications of advanced image and histological techniques revealed the presence of cortical alveoli oocytes (CAO), which prevailed as the most advanced oocyte phase for 4–5 months. This new finding of an extended and early appearance of CAOs in this gadoid was supported by that vitellogenesis first started to appear 3 months later. The subsequent oocyte growth trajectories indicated that larger individuals [total length (TL) = 70 cm] typically spawn in the order of 3 weeks earlier than the smaller ones (TL = 40 cm). The spawning season appeared stretched over about 3 months. The majority of skipping females arrested oocyte growth at the CAO phase followed by atretic reabsorption. Compared to those individuals maturing for the spawning season, ‘skippers’ generally exhibited lower body condition, characterized also by relatively lower liver sizes at the time of the main spawning season. This study demonstrated well-developed skipping dynamics, but also that the CAO period, i.e., when skipping takes place, may be exceedingly long in this commercially valuable gadoid and that its reproductive cycle in many ways deviates from that of the data-rich, sympatric NEA cod (Gadus morhua). publishedVersion

The collection and presentation of accurate reproductive data from wild fish has historically been somewhat problematic, especially for serially spawning species. Therefore, the aim of the current study was to develop a novel method of assessing female spawning status that is robust to variation in oocyte dynamics between specimens. Atlantic cod (Barents Sea stock) were used to develop the new ‘ultrametric’ method, that is based on the progressive depletion of the vitellogenic oocyte pool relative to the rather constant previtellogenic oocyte (PVO) pool. Fish were subsequently partitioned into one of four categories that accurately reflected changes in their oocyte size frequency distribution characteristics and gonadosomatic index throughout spawning. The ultrametric method overcomes difficulties associated with presence of bimodal oocyte distributions, oocyte tails, lack of clear hiatus region, and presence of free ova, and can be implemented at a single sampling point. Much of the workflow is fully automated, and the technique may circumvent the need for histological analysis depending on the desired outcome. The ultrametric method differs from the traditional autodiametric method in that PVOs can be separated by ultrasonication and then enumerated, and ovarian homogeneity is not a mandatory requirement per se. The method is designed for determinate spawners but might be extended to include indeterminate spawners.

International audience; One of the keys for an optimal Eurasian perch aquaculture broodstock management is being able to determine the sex of individuals. For Eurasian perch, compared with other methods of sex identification of fish and according to the 3R principle (replacement, reduction and refinement), ultrasonography is a rapid, non-lethal, non-invasive and accurate method. During two successive experiments, we used ultrasound to identify the gender of two immature Eurasian perch broodstock. In the last experiment, females were identified with 98.9% accuracy (n = 180) and males with 98.8% accuracy (n = 92). This method can be very beneficial for perch fish farmers or aquaculture research.

Impacts of climate change on ocean productivity sustaining world fisheries are predominantly negative but vary greatly among regions. We assessed how 39 fisheries resources—ranging from data-poor to data-rich stocks—in the North East Atlantic are most likely affected under the intermediate climate emission scenario RCP4.5 towards 2050. This region is one of the most productive waters in the world but subjected to pronounced climate change, especially in the northernmost part. In this climate impact assessment, we applied a hybrid solution combining expert opinions (scorings)—supported by an extensive literature review—with mechanistic approaches, considering stocks in three different large marine ecosystems, the North, Norwegian and Barents Seas. This approach enabled calculation of the directional effect as a function of climate exposure and sensitivity attributes (life-history schedules), focusing on local stocks (conspecifics) across latitudes rather than the species in general. The resulting synopsis (50–82°N) contributes substantially to global assessments of major fisheries (FAO, The State of World Fisheries and Aquaculture, 2020), complementing related studies off northeast United States (35–45°N) (Hare et al., PLoS One, 2016, 11, e0146756) and Portugal (37–42°N) (Bueno-Pardo et al., Scientific Reports, 2021, 11, 2958). Contrary to prevailing fisheries forecasts elsewhere, we found that most assessed stocks respond positively. However, the underlying, extensive environmental clines implied that North East Atlantic stocks will develop entirely different depending upon the encountered stressors: cold-temperate stocks at the southern and Arctic stocks at the northern fringes appeared severely negatively impacted, whereas warm-temperate stocks expanding from south were found to do well along with cold-temperate stocks currently inhabiting below-optimal temperatures in the northern subregion.

BackgroundEphippidae fish are characterized by a discoid shape with a very small visceral cavity. Among themPlatax orbicularishas a high economic potential due to its flesh quality and flesh to carcass ratio. Nonetheless, the development of its aquaculture is limited by high mortality rates, especially due toTenacibaculum maritimuminfection, occurring one to three weeks after the transfer of fishes from bio-secure land-based aquaculture system to the lagoon cages for growth. Among the lines of defense against this microbial infection, the gastrointestinal tract (GIT) is less studied. The knowledge about the morphofunctional anatomy of this organ inP. orbicularisis still scarce. Therefore, the aims of this study are to characterize the GIT in non-infectedP. orbicularisjuveniles to then investigate the impact ofT. maritimumon this multifunctional organ.MethodsIn the first place, the morpho-anatomy of the GIT in non-infected individuals was characterized using various histological techniques. Then, infected individuals, experimentally challenged byT. maritimumwere analysed and compared to the previously established GIT reference.ResultsThe overlapped shape of the GIT ofP. orbicularisis probably due to its constrained compaction in a narrow visceral cavity. Firstly, the GIT was divided into 10 sections, from the esophagus to the rectum. For each section, the structure of the walls was characterized, with a focus on mucus secretions and the presence of the Na+/K+ATPase pump. An identification key allowing the characterization of the GIT sections usingin totohistology is given. Secondly, individuals challenged withT. maritimumexhibited differences in mucus type and proportion and, modifications in the mucosal and muscle layers. These changes could induce an imbalance in the trade-off between the GIT functions which may be in favour of protection and immunity to the disadvantage of nutrition capacities.

Cloud cover is crucial information for many applications such as planning land observation missions from space. It remains however a challenging variable to forecast, and Numerical Weather Prediction (NWP) models suffer from significant biases, hence justifying the use of statistical post-processing techniques. In this study, ARPEGE (M\'et\'eo-France global NWP) cloud cover is post-processed using a convolutional neural network (CNN). CNN is the most popular machine learning tool to deal with images. In our case, CNN allows the integration of spatial information contained in NWP outputs. We use a gridded cloud cover product derived from satellite observations over Europe as ground truth, and predictors are spatial fields of various variables produced by ARPEGE at the corresponding lead time. We show that a simple U-Net architecture produces significant improvements over Europe. Moreover, the U-Net outclasses more traditional machine learning methods used operationally such as a random forest and a logistic quantile regression. We introduced a weighting predictor layer prior to the traditional U-Net architecture which produces a ranking of predictors by importance, facilitating the interpretation of the results. Using $N$ predictors, only $N$ additional weights are trained which does not impact the computational time, representing a huge advantage compared to traditional methods of ranking (permutation importance, sequential selection, ...)., Comment: 32 pages, 12 figures

Ambient temperature modulates reproductive processes, especially in poikilotherms such as teleosts. Consequently, global warming is expected to impact the reproductive function of fish, which has implications for wild population dynamics, fisheries and aquaculture. In this extensive review spanning tropical and cold-water environments, we examine the impact of higher-than-optimal temperatures on teleost reproductive development and physiology across reproductive stages, species, generations and sexes. In doing so, we demonstrate that warmer-than-optimal temperatures can affect every stage of reproductive development from puberty through to the act of spawning, and these responses are mediated by age at spawning and are associated with changes in physiology at multiple levels of the brain-pituitary-gonad axis. Response to temperature is often species-specific and changes with environmental history/transgenerational conditioning, and the amplitude, timing and duration of thermal exposure within a generation. Thermally driven changes to physiology, gamete development and maturation typically culminate in poor sperm and oocyte quality, and/or advancement/delay/inhibition of ovulation/spermiation and spawning. Although the field of teleost reproduction and temperature is advanced in many respects, we identify areas where research is lacking, especially for males and egg quality from "omics" perspectives. Climate-driven warming will continue to disturb teleost reproductive performance and therefore guide future research, especially in the emerging areas of transgenerational acclimation and epigenetic studies, which will help to understand and project climate change impacts on wild populations and could also have implications for aquaculture.

The domestication process is accompanied by adaptation of the animals to captive conditions. It induces changes at different levels thereby affecting a variety of biological functions. While there is abundant literature on the domestication effects on growth and stress response in teleosts, the effects on reproduction have received limited attention. In this work, we investigated the domestication effect on the reproductive ability of Eurasian perch (Perca fluviatilis L.), a promising candidate for the development of European aquaculture and whose reproductive physiological processes through the domestication history have not been questioned yet. To address this question, two populations of F1 and “domesticated” females were subjected to a photothermal program allowing the control of gonadogenesis advancement. Gonadosomatic index, 17β-Estradiol levels, and oocyte diameter were significantly higher in the “domesticated” population than in F1 population. In contrast, testosterone, 11-ketotestosterone, and vitellogenin levels were found to be higher in F1 females than in their “domesticated” counterparts. Lower reproductive performance was observed in the “domesticated” population compared to the F1 population in terms of embryo survival, percentage of eyed-stage larvae, hatching and percentage of malformation rates. In conclusion, this study shows that despite a positive effect on advancing gonadogenesis and vitellogenesis, this domestication route negatively affected the reproductive performance under our conditions. Statement of relevance This work will give information to producers to choose good broodstock populations (wild or domesticated) to have optimal reproductive performances in Eurasian perch, and thus improve fish production.

Improving reproductive protocols is one crucial step towards aquaculture expansion of pikeperch (Sander lucioperca), which is still characterised by variable and/or low spawning effectiveness. One of the main challenges is to synchronise ovulation at a precisely planned time with a consistently satisfactory reproductive outcome. To this end, the present study examined the effect of different spawning agents (human chorionic gonadotropin [hCG] and salmon gonadotropin-releasing hormone analogue [sGnRHa]) with different doses and application modes (including double injection). The study covered three consecutive spawning seasons, which corresponded to three distinct experiments, where domesticated pikeperch broodstock, commercially grown in a recirculating aquaculture system, was used. In the first year of the study, the effect of different doses of sGnRHa (10, 25 and 50 μg kg−1) and hCG (250, 500 and 1000 IU kg−1) on the reproductive performance of the domesticated broodstock was evaluated. The results were also compared with literature data for wild fish. During the second and third years, typical indicators of spawning performance (ovulation rate, latency time and egg quality) were followed when a double sGnRHa injection was compared to a single 50 μg kg−1 or 500 IU kg−1 injection of sGnRHa or hCG, respectively; the best results were obtained in the first and second experiments. The results of the present study clearly indicate that various hormonal treatments effectively induced domesticated pikeperch ovulation, although highly variable egg quality was observed throughout the three spawning seasons (maximum hatching rates were 60.6 ± 11.5, 37.7 ± 28.9 and 49.1 ± 24.7% in the first, second and third years of the study, respectively). However, additional analysis of the data from the entire study revealed for the first time that a significant proportion of the lower-quality eggs came from fish that responded ‘early’ to hormonal treatment (

Fasting and refeeding occur naturally in predators but this is largely ignored when dealing with farmed fish. Therefore, the effects of 3-week fasting and re-alimentation (2.5% of the individual body mass) were investigated using two genetically selected populations (F2 generation) of 250 g juvenile sea bass (Dicentrarchus labrax L.). Blood osmolarity, gill and intestinal morphology and expression of the sodium pump (Na+, K+-ATPase, NKA) were studied on two phenotypes showing different degrees of body mass loss during food deprivation: one group losing body mass rapidly during fasting (F +) and the other one limiting body mass loss during the same period (F −). Blood osmotic pressure significantly decreases due to re-alimentation in both groups, but this is compensated in the F + group. In this group, gill ionocytes are smaller and less numerous, but a significantly higher NKA gene expression is noted in the gills in comparison to the F − individuals 48 and 72 h after re-alimentation, and also in the posterior intestine 72 h after re-alimentation. This most probably occurs to compensate for a higher salt intake during nutrient absorption in comparison to the F − group. Furthermore, refed F − fish absorb more lipids along the proximal anterior intestine, and take longer to digest than the F + group, and show enterocyte vacuolization in the posterior intestine. Therefore, the two selected populations have different postprandial digestive strategies: the F − fish optimize feed efficiency first at the cost of optimal hydromineral adjustment, while the F + group invests in osmoregulatory performance at the expense of digestive physiology. Statement of relevance Our paper is highly relevant to the general field of commercial aquaculture. There is an increasing number of research articles dealing with fasting and refeeding in commercial fish and how to improve fish nutrition based on these physiological data and genetic selection.

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During the teleost ontogenesis, biotic and abiotic factors influence organs deformations. Despite of an important literature, the potential causes of deformities in fish are still poorly understood. Cultured fish in artificial conditions exhibit higher incidence of developmental impairments compared to wild ones. This study aims at describing exhaustively the deformity categories of newly hatched embryos of Eurasian perch and investigating at once all biotic and abiotic factors of two extremely different rearing systems [recirculating aquaculture system (RAS) vs. ponds] on their occurrence. The description and clustering of deformities according to the organs involved allowed not only to show that skeletal, cardiac and yolk anomalies are the most common ones, but also to highlight new functions undergoing developmental failure (locomotive, digestive and excretory systems). In total, 10 categories of abnormalities have been described. In addition, our data show a relationship between the cardiac and yolk deformities suggesting common causes. In a second part, we compared the incidence of deformities in the progeny of two distinct populations of fish, reared under extremely various conditions (RAS vs. pond). The total deformity rates did not differ between the groups but the nature of deformities was surprisingly different as the RAS reared fish (RRF) originating from fisheries presented a higher variety of deformity categories than the fish originating from Lorraine ponds (LPRF). Indeed, cardiac, yolk and skeletal axis deformities were more frequent in RRF embryos, whereas mouth abnormalities were preferentially represented in LPRF embryos. These findings may help understanding the potential causes of these developmental impairments in cultured animals and may lead to the improvement of husbandry conditions.

International audience; We propose a simple microfluidic device able to separate submicron particles (critical size ~0.1 µm) from a complex sample with no filter (minimum channel dimension being 5 µm), by hydrodynamic filtration. A model taking into account the actual velocity profile and hydrodynamic resistances enables predicting the chip sorting properties for any geometry. Two design families are studied to obtain (i) small sizes within minutes (low-aspect ratio, two-level chip) and (ii) micron-sized sorting with µL flowrate (3D architecture based on lamination). We obtain quantitative agreement of sorting performances both with experiments and with numerical solving, and determine the limits of the approach. We therefore demonstrate a passive, filter-less sub-micron size sorting with simple, robust, easy to fabricate design.

International audience; The behaviour of a vesicle suspension in a simple shear flow between plates (Couette flow) was investigated experimentally in parabolic flight and sounding rocket experiments by Digital Holographic Microscopy. The lift force which pushes deformable vesicles away from walls was quantitatively investigated and is found to be rather well described by a theoretical model by Olla [1]. At longer shearing times, vesicles reach a steady distribution about the center plane of the shear flow chamber, through a balance between the lift force and shear induced diffusion due to hydrodynamic interactions between vesicles. This steady distribution was investigated in the BIOMICS experiment in the MASER 11 sounding rocket. The results allow an estimation of self-diffusion coefficients in vesicle suspensions and reveal possible segregation phenomena in polydisperse suspensions.

While 384 well-plate format is still commonly used by the Biomolecular community, miniaturized formats (1536 and 3456 well-plates) are gaining in popularity, due to promise of higher throughput and lower reagent consumption. However, decrease in reagent volume in such miniaturized formats leads to issues of accuracy and sensitivity caused by incomplete mixing and the mechanical stirring methods satisfactory used for 384 well-plate formats, give poor mixing with lower volumes. Here we present results obtained in 1536-well and 3456-well plates equipped with electrodes where we induced fluid flow by the action of electromagnetic fields. Improvement in two types of reactions are obtained, related to ELISA-type assays and kinase-based assays. For example, in the kinase reaction, we show that, when using the electrode-enabled mixing technology, an 8 minutes protocol in 1536-well plate format is equivalent in accuracy to a 90 minutes protocol in standard 96-well plate format mixed using an orbital shaker. This mixing technology is scalable, due to modern developments in electrode manufacturing and can be used in super-high throughput screening formats, such as 10000-well or droplets.Copyright © 2009 by ASME

International audience; We report on the rheology of dilute suspensions of red blood cells (RBC) and vesicles. The viscosity of RBC suspensions reveals a previously unknown signature: it exhibits a pronounced minimum when the viscosity of the ambient medium is close to the value at which the transition from tank-treading to tumbling occurs. This bifurcation is triggered by varying the viscosity of the ambient fluid. It is found that the intrinsic viscosity of the suspension varies by about a factor of 4 in the explored parameter range. Surprisingly, this significant change of the intrinsic viscosity is revealed even at low hematocrit (5%). We suggest that this finding may be used to detect blood flow disorders linked to pathologies that affect RBC shape and mechanical properties. This opens future perspectives on setting up new diagnostic tools, with great efficiency even at very low hematocrit. Investigations are also performed on giant vesicle suspensions, and compared to RBCs.

The dynamics of a vesicle suspension in a shear flow between parallel plates has been investigated under microgravity conditions, where vesicles are only submitted to hydrodynamic effects such as lift forces due to the presence of walls and drag forces. The temporal evolution of the spatial distribution of the vesicles has been recorded thanks to digital holographic microscopy, during parabolic flights and under normal gravity conditions. The collected data demonstrates that vesicles are pushed away from the walls with a lift velocity proportional to $\dot{\gamma} R^3/z^2$ where $\dot{\gamma}$ is the shear rate, $R$ the vesicle radius and $z$ its distance from the wall. This scaling as well as the dependence of the lift velocity upon vesicle aspect ratio are consistent with theoretical predictions by Olla [J. Phys. II France {\bf 7}, 1533--1540 (1997)]., Comment: 6 pages, 8 figures

Colloque avec actes et comité de lecture. Internationale.; International audience; Giant vesicles are deformable lipid membranes enclosing a fluid, with diameters of several microns. They are useful models for the study of biological flows. Their behaviour under shear flow reveals a complex dynamics involving several regimes: stationary tank-treading motion, periodic fliping or tumbling motion, and periodic vacillating-breathing motion. Our experimental study reveals that the deformability of vesicles strongly influences the dynamics. One noticeable feature is a slowing down of the tumbling motion with respect to the shear rate when the latter increases. A semi-phenomonological model including the deformability of objects helps understand the connection between the slowing down of the tumbling motion and a coupling between rotation and deformation. A new vacillating-breathing motion is also predicted and a complex phase diagram can be established.

Dynamics of vesicle and red blood cell suspensions in simple shear and microfluidic flows., Dynamique de suspensions de vésicules et de globules rouges en écoulement de cisaillement simple et en microfluidique.

The flow of giant lipid vesicles through cylindrical capillaries is experimentally investigated. Vesicles are deflated with reduced volumes between 0.8 and 1, corresponding to prolate spheroidal equilibrium shapes. Both interior and exterior fluids are sugar solutions with viscosities close to 10−3 Pa s. Vesicles are aspirated into a capillary tube with a diameter close to the vesicle size and a constant flow rate is imposed. Significant deformation of the membrane occurs and increases when the velocity, confinement or deflation of the vesicle are increased. The mobility of vesicles, defined as the ratio of their velocity to the average velocity of the fluid is a decreasing function of confinement. Our experimental system provides a controllable and flexible tool to investigate deformability effects responsible for crucial aspects of blood rheology in capillaries.