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Eight juvenile European seabass were exposed to two thermal ramping protocols with different levels of aerobic activity and tolerance endpoint: the critical thermal maximum for swimming (CTSmax) while exercising aerobically until fatigue, and the critical thermal maximum (CTmax) under static conditions until loss of equilibrium (LOE). In the CTSmax, warming caused a profound increase in oxygen uptake rate (M˙O2) culminating in a gait transition, from steady aerobic towards unsteady anaerobic swimming, then fatigue at 30.3±0.4°C (mean±SE). Gait transition and fatigue presumably indicate an oxygen limitation, an inability to meet the combined demands of swimming plus warming. The CTmax also elicited an increase in M˙O2, culminating in LOE at 34.0±0.4°C, significantly warmer than fatigue at CTSmax. The maximum M˙O2 achieved in the CTmax was, however, less than 30% of that achieved in the CTSmax. Therefore, the static CTmax did not exploit full cardiorespiratory capacity for oxygen supply, indicating that LOE was not caused by systemic oxygen limitation. Consequently, systemic oxygen supply can be significant for tolerance of acute warming in seabass but this depends upon the physiological context and the endpoint used.

International audience; Fish oocyte development monitoring is a mandatory operation when studying breeding in captivity as well as in the wild. In aquaculture, it is required to determine the best fertilization time. In the wild, it helps to detect spawning grounds, the distribution of fish species and the interaction between animals and their environment. In both settings, the conventional technique for developmental stage identification consists of handling the fish for oocyte sampling and sample observation using a binocular zoom head. Such an operation is difficult for the operator as well as for the fish. There is a need for repeated anesthesia and oocyte sampling, and it relies on operator expertise to identify the developmental stage. In this context, this publication proposes, for the first time, to study the potential of bioimpedance measurement as an alternative in fish breeding studies. We have set up an experiment combining the in vitro bioimpedance measurement of sampled oocytes with the conventional estimation technique for 69 sampled collected on farmed European sea bass. The statistical analysis has demonstrated that three of the four main developmental stages can be identified using bioimpedance measurement. The integrability of the bioimpedance technique with its implantable sensor makes this potential alternative approach very promising. Thanks to this sensor it could be possible, for the first time ever, to monitor in vivo the oocyte developmental stage in captivity as well as in the wild.

International audience

The European sea bass (Dicentrarchus labrax) exhibits female-biased sexual size dimorphism (SSD) early in development. New tagging techniques provide the opportunity to monitor individual sex-related growth during the post-larval and juvenile stages. We produced an experimental population through artificial fertilization and followed a rearing-temperature protocol (~16°C from hatching to 112 days post-hatching, dph; ~20°C from 117 to 358 dph) targeting a roughly balanced sex ratio. The fish were tagged with microchips between 61 and 96 dph in five tagging trials of 50 fish each; individual standard length (SL) was recorded through repeated biometric measurements performed between 83 to 110 dph via image analyses. Body weight (BW) was modelled using the traits measured on the digital pictures (i.e. area, perimeter and volume). At 117 dph, the fish were tagged with microtags and regularly measured for SL and BW until 335 dph. The experiment ended at 358 dph with the sexing of the fish. The sex-ratio at the end of the experiment was significantly in favor of the females (65.6% vs. 34.4%). The females were significantly longer and heavier than the males from 103 dph (~30 mm SL, ~0.44 g BW) to 165 dph, but the modeling of the growth curves suggests that differences in size already existed at 83 dph. A significant difference in the daily growth coefficient (DGC) was observed only between 96 and 103 dph, suggesting a physiological or biological change occurring during this period. The female-biased SSD pattern in European sea bass is thus strongly influenced by very early growth differences between sexes, as already shown in previous studies, and in any case long before gonadal sex differentiation has been started, and thus probably before sex has been determined. This leads to the hypothesis that early growth might be a cause rather than a consequence of sex differentiation in sea bass.

International audience; Viral Nervous Necrosis (VNN) is a major threat for the European sea bass (Dicentrarchus labrax) aquaculture industry. The improvement of disease resistance through selective breeding is a promising option to reduce outbreaks. With the development of high-throughput genotyping technologies, identification of genomic regions involved in the resistance could improve the efficiency of selective breeding. The aim of this study was to identify quantitative trait loci (QTL) involved in VNN resistance and to quantify their effect.Four experimental backcross families comprising 378, 454, 291 and 211 individuals and two commercial populations A and B comprising 1027 and 1042 individuals obtained from partial factorial crosses (59 male x 20 female for pop A; 39 male x 14 female for pop B) were submitted to a redspotted grouper nervous necrosis virus (RGNNV) challenge by bath. A high-density single nucleotide polymorphism (SNP) chip panel was designed to develop the ThermoFisher Axiom (TM) 57k SNP DlabChip, which was used for genotyping all individuals and building a high quality linkage map. In the backcross families, composite interval mapping was performed on 30,917, 23,592, 30,656 and 31,490 markers, respectively. In the commercial populations, 40,263 markers in pop A and 41,166 markers in pop B were used to perform genome-wide association studies (GWAS) using a GBLUP and a BayesC pi approach.One QTL was identified on chromosome LG12 in three of the four experimental backcross families, and one additional QTL on LG8 was detected in only one family. In commercial populations, QTL mapping revealed a total of seven QTLs, among which the previously mentioned QTL on LG12 was detected in both. This QTL, which was mapped to an interval of 3.45 cM, explained 9.21% of the total genetic variance in pop A, while other identified QTLs individually explained less than 1% of the total genetic variance.The identification of QTL regions involved in VNN resistance in European sea bass, with one having a strong effect, should have a great impact on the aquaculture industry. Future work could focus on the fine mapping of the causal mutation present on LG12 using whole genome sequencing.

Visioconference - Online Meeting; International audience

International audience; Koi herpesvirus disease (KHVD) is currently the most serious threat to global carp farming. Prevention is a sensible strategy for tackling this disease and improved genetic resistance of carp strains is a desirable breeding goal. To study the potential for multitrait selection, the objective of the current study was to estimate the genetic correlations between KHVD resistance and production traits in Amur mirror carp. A total of 1500 fingerlings from four factorial crosses of five dams and ten sires were challenged with Koi herpesvirus (KHV). Juvenile growth-related traits were collected on the same individuals before the challenge test. Production traits were measured on siblings of the challenged population at different life stages (yearling to market size). The estimated heritability for resistance to KHVD was 0.43 ± 0.08 on the observed scale and 0.72 ± 0.13 on the underlying liability scale. Most genetic correlations between KHVD resistance and important production traits were insignificant, showing that selection for improved production traits would not increase susceptibility to KHV and vice versa. However, resistance to KHVD was negatively correlated with Fulton's condition factor (FC) after the second overwintering and relative head length (RHL), relative body height (RBH) and relative body width (RBW) from the second growing season to the market size, with a more prolonged body shape of Amur mirror carp (genes from Amur wild scaly carp, Cyprinus rubrofuscus) being associated with higher KHVD resistance. Intermediate favorable genetic correlations between KHVD resistance and log-log residuals of headless carcass yield (0.37 ± 0.14) and fillet yield (0.44 ± 0.13) at market size suggested that selection for improved yields of edible body parts might indirectly lead to a slight improvement in KHVD resistance and vice versa.

Morphological predictors of slaughter yields using 3D digitizer and their utilization in common carp breeding program. Aquaculture Europe 2019

The relationship between koi herpesvirus disease resistance and other production traits inferred from sibling performance in amur mirror carp. Aquaculture Europe 2019

International audience; Viral Nervous Necrosis (VNN) disease is considered as one of the most serious threats for European sea bass cultured in Mediterranean Sea, with no simple and effective procedures to treat this disease. In this study, 1472 offspring resulting from artificial full factorial mating of western Mediterranean dams with sires from four different wild populations of European sea bass (Northern Atlantic, NAT; Western Mediterranean, WEM; Northern-East Mediterranean, NEM; and Southern-East Mediterranean, SEM) were challenged by experimental infection to W80 betanodavirus strain in order to evaluate genetic variations for VNN resistance among populations and genetic correlations between VNN resistance and production traits. The results showed a large variation of VNN resistance between the four populations tested as well as between sire families within strain. The survivals between pure wild populations SEM, NEM, WEM and NAT were estimated at 99%, 94%, 62%, and 44%, respectively. A moderate intra-population heritability of VNN resistance, calculated based on liability scale with sire model, was recorded for the first time in European sea bass (h2 u =0.26 ± 0.11). Finally, moderate negative genetic correlations between VNN resistance and daily growth coefficient (DGC) and body weight (BW) were also demonstrated (−0.28 ± 0.20, −0.35 ± 0.14, respectively) while the genetic correlation between resistance to VNN and fillet adiposity (FA) was weakly negative and not significant (−0.13 ± 0.19). These results give good prospects of selective breeding of European sea bass for improved resistance to VNN disease.

International audience; Slaughter yields are traits of high interest especially for fish species sold in processed form like headless carcass or fillets, as well as with regard to increasing consumer preference for easy-to-prepare fish products. However, slaughter yields cannot be measured on live fish and thus their genetic improvement through mass selection is impossible. The usual alternatives are sib selection and/or indirect selection on correlated traits or morphological predictors of slaughter yields. In the present study, we assessed the possibility of using a combination of 3D digitized landmarks and ultrasound measurements in genetic improvement of slaughter yields in common carp. DNA – pedigreed market-size carp (n = 1553 fish) were produced from a partial factorial design of 20 dams and 40 sires. Morphological predictors were recorded in real-time using a 3D digitizer and ultrasound tomography, and combined by multiple linear regression to predict slaughter yields. The 3D model-predicted headless carcass and fillet yields explained 59% and 50%, respectively, of the total phenotypic variation in slaughter yields. Genetic parameters of model-predicted yields and of the best individual predictor (3D_P2 – ratio between abdominal fillet thickness – E8 and external 3D ventral height) were similar or slightly lower when compared to previous 2D-based predictors (Prchal et al., 2018a, 2018b, 2018c). This was also the case for the expected genetic gain using indirect selection on the same simple predictor for fillet yield improvement (0.48% fillet units for 3D vs. 0.52% for 2D). 3D model-predicted yields and especially simple predictors thus have a solid potential for genetic improvement of slaughter yields in common carp. While they are not better than 2D predictors, they are much more convenient and faster to collect in the field, as they do not imply post-processing of images. These practical aspects should be taken into account in the future carp breeding program.

International audience; Individual tagging is key to a better understanding of early life stages in fish. Very small RFID transponder microchips (500 x 500 x 100 mu m, 82 mu g) are now available. The aim of this study was to develop a protocol to tag European sea bass (Dicentrarchus labrax L.) larvae from 61 days post-hatching (dph; standard length similar to 10 mm) to 96 dph (standard length similar to 28 mm) through intra-coelomic implantation of microchips. The suitability of such a tagging procedure was evaluated, with the purpose of determining the minimal fish age and body size for microchip tagging without adverse effects on survival and growth performance.We produced an experimental population composed by 50:50 normally pigmented larvae and albino larvae through artificial fertilization. Five tagging trials were performed over 35 days, in fish aged 61, 75, 83, 89 and 96 dph. Each time, 50 normally pigmented fish were tagged, while 50 albino fish were used as controls. Mortality was recorded daily, while biometric measurements were performed at 75, 83, 89, 96, 103 and 110 dph via image analysis.Microchip tagging was possible in larvae from an age of 75 dph (standard length similar to 20 mm), with satisfactory performance in terms of survival rate (between 84 and 98% 24 h after tagging) and growth rate, and without significant differences in comparison with the untagged controls. In contrast, tagging before 75 dph is not to be recommended, as the age group 61 dph was the most affected in terms of survival (only 62% of fish survived 24 h after tagging) and growth rate, showing significant differences compared to the untagged controls. The overall microchip reading success rate for the age groups throughout the experiment was 51.4%, the overall reading success rate at each biometric measurement was 48.2%, probably due to the change in orientation of the microchip inside the fish body cavity.The tagging protocol developed was then overall successful, albeit with a moderate reading success. Precocious tagging could allow the collection of new types of data (individual, longitudinal) related to larval development, behavioral studies, physiological and immunological investigations. Future tests could focus on the effects of tagging on baseline locomotion and behavior, as well as the suitability and the efficiency of intramuscular microchip tagging on larger fish.

The aquaculture industry has increasingly aimed at improving economically important traits like growth, feed efficiency and resistance to infections. Artificial selection represents an important window of opportunity to significantly improve production. However, the pitfall is that selection will reduce genetic diversity and increase inbreeding in the farmed stocks. Genetic tools are very useful in this context as they provide accurate measures of genetic diversity together with many additional insights in the stock status and the selection process. In this study we assessed the level of genetic variability and relatedness over several generations of two lines of experimentally selected European sea bass (Dicentrarchus labrax L.). The first line was selected for growth over three generations and the second line for both high and low weight loss under a starvation regime over two generations. We used a genomic approach (2549 single nucleotide polymorphism markers derived from double digest restriction site associated DNA sequencing) in combination with eight microsatellites to estimate genetic variation, relatedness, effective population size and genetic differentiation across generations. Individual heterozygosity estimates indicated that the selected lines showed no significant reduction in diversity compared with wild populations. There was, however, a decreasing trend in allelic richness, suggesting the loss of low frequency alleles. We compared the estimates of effective population size from genetic markers with pedigree information and found good correspondence between methods. This study provides important insights in the genetic consequences of selective breeding and demonstrates the operational use of the latest genomic tools to estimate variability, inbreeding and at a later stage domestication and artificial selection.

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.

Genetic parameters for carcass and fillet percentage were estimated in 760 European sea bass reared under commercial conditions and slaughtered at 573 days post fertilization (395 g mean body weight). Phenotyped fish were the offspring of 45 sires and 20 dams crossed in a factorial mating design. Pedigrees were re-constructed with 90.7% success using 12 microsatellites. The heritability of fillet yield was moderately low (0.21), while it was high for carcass yield (0.57). Both traits were poorly correlated (− 0.01 to 0.28) making space for their combined improvement. We investigated different predictors derived from measurement of surfaces on digital pictures and ultrasound measurements at several points of the body. The accuracy of the phenotypic prediction was rather low for fillet yield (r2 = 0.02–0.18), but higher for carcass yield (r2 = 0.27–0.41). However, genetic correlations of predictors with the traits to predict were reasonably high (up to 0.67 for fillet yield and 0.95 for carcass yield), thus allowing to consider them for performing indirect individual selection instead of sib selection. However, it was difficult to design a predictor that would simultaneously increase fillet yield and carcass yield because of contradicting effects of relative head size, an important component of the predictors which was positively correlated to carcass yield but not to fillet yield. Statement of relevance We estimated phenotypic predictors for processing yields in the European sea basslane estimated their genetic variation and correlations with the traits to predict. This is important to be able to apply indirect selection for processing yields in this species. This showed that although the traits of interest were hardly correlated, it was not possible to find external predictors having a significant positive impacts on both traits (carcass and fillet yield) simultaneously. This highlights the need to study specifically these issues in different species and conditions, as the picture here is very different to the well studied case of rainbow trout for example.

Ajouter clé UT WOS; Describing and explaining the geographic within-species variation in phenotypes ("phenogeography") in the sea over a species distribution range is central to our understanding of a variety of eco-evolutionary topics. However, phenogeographic studies that have a large potential to investigate adaptive variation are overcome by phylogeographic studies, still mainly focusing on neutral markers. How genotypic and phenotypic data could covary over large geographic scales remains poorly understood in marine species. We crossed 75 noninbred sires (five origins) and 26 dams (two origins; each side of a hybrid zone) in a factorial diallel cross in order to investigate geographic variation for early survival and sex ratio in the metapopulation of the European sea bass (Dicentrarchus labrax), a highly prized marine fish species. Full-sib families (N = 1,950) were produced and reared in a common environment. Parentage assignment of 7,200 individuals was performed with seven microsatellite markers. Generalized linear models showed significant additive effects for both traits and pleiotropy between traits. A significant nonadditive genetic effect was detected. Different expression of traits and distinct relative performances were found for reciprocal crosses involving populations located on each side of the main hybrid zone located at the Almeria-Oran front, illustrating asymmetric reproductive isolation. The poor fitness performance observed for the Western Mediterranean population of sea bass is discussed as it represents the main source of seed hatchery production, but also because it potentially illustrates nonadaptive introgression and maladaptation.

Aquaculture of carnivorous species has strongly relied on fish meal and fish oil for feed formulation; however, greater replacement by terrestrial plant-based products is occurring now. This rapid change in dietary environment has been a major revolution and has to be taken into consideration in breeding programs. The present study analyzes potential consequences of this nutritional tendency for selective breeding by estimating genetic parameters of BW and growth rates estimated by the thermal growth coefficient (TGC) over different periods with extremely different diets. European sea bass (Dicentrarchus labrax L.) from a factorial cross (1,526 fish) between 25 sires and 9 dams were used to estimate heritabilities and genotype by diet interaction. Starting 87 d after fertilization (2.5 g), one-half of the sea bass were fed a diet containing marine products (M), and the other one-half were fed a totally plant-based (PB) diet (without any fish meal or fish oil). The fish were individually tagged, reared in a recirculated system, and genotyped at 13 microsatellites to rebuild parentage of individuals. Body weight and TGC were measured for 335 d until fish fed the M diet reached 108.3 g of BW. These traits were significantly less in fish fed the PB diet (P 0.1). Survival was significantly less in fish fed the PB diet (PB=64.7%, M=93.7% after 418 d, P

International audience; Biological variability is no longer considered as statistical noise, but rather as an adaptive benefit. This variability comes from consistent differences in behavioral and physiological responses among individuals to a changing/challenging environment, named “coping style”, “temperament” or “personality”. Many studies have described how to characterize personality traits and how to assess their consistency over time and between different contexts; however, little is known about the environmental factors shaping personality development. Because contrasting personalities are maintained with evolution, this lead to the widespread assumption that genes play a predominant role in personality. In many cases, personality traits are however also likely to be determined by individual experience, which is probably at least as important as genetics in shaping personality. The aim of this study was to assess how environmental variability (herein food predictability) impacts behavioral responses, particularly the shyness-boldness axis, one of the most widely shared animal personality trait. Here, we reared juvenile seabass (95 days old) from two divergent strains selected for feed deprivation tolerance under standard conditions for 40 days. Thereafter, we submitted them to two feeding treatments (Predictable versus Unpredictable) starting at 135 dph and lasting 60 days. Seabass reared under a predictable food supply (PFS) grew faster and were shyer than fish reared under an unpredictable food supply (UFS) (i.e. they took more time to exit the refuge zone of a Z-maze; UFS: 132.47 ± 34.63 s; PFS: 336.79 ± 56.97 s) but their exploration tendency was similar. We also examined the behavioral responses of these fish facing a hypoxic challenge. Hypoxia tolerance results were consistent before and after the two feeding treatments. Our findings show the importance of early environmental experience as a driving force shaping boldness. In addition, we provide further evidence that predictable feeding time should be respected in studies assessing essential functions such as growth and behavior. Although personality traits are partially heritable, this study demonstrates the important influence of environmental conditions and life history on behavior.

Sea bass is a major species in Mediterranean aquaculture, and is now being subject to selective breeding programmes for faster growth. In terrestrial species, it was demonstrated that fast growth may be linked to a correlated degradation of fitness traits. In this experiment, we evaluated 600 young sea bass from a factorial mating of 76 sires and 13 dams. The sires were from four genetic groups, wild (W), domesticated (D), and selected for growth (2 groups, M and P). The 600 offspring were submitted to two acute confinement stress challenges at 6 weeks intervals, and plasma cortisol at one hour post stress was measured. The same fish were also submitted to two swimming challenges at a 5 days interval, where the maximum sustained swimming speed ( U max ) of each fish was evaluated. Parentage was assessed by genotyping of 12 microsatellites. 554 fish had both valid parentage and phenotypes. Cortisol had a low repeatability (r = 0.30 between the two successive measurements) while repeatability was moderate for U max (r = 0.62). However, genetic correlations between successive measurements were very high (> 0.96) for both traits, indicating that successive measurements were related to the same trait. Heritability was moderate for mean post-stress cortisol (h 2 = 0.34 ± 0.09) and U max (h 2 = 0.48 ± 0.08). When U max was expressed in m.s − 1 , it was negatively correlated to cortisol (r A = − 0.48 ± 0.08) and weakly correlated to body weight (r A = 0.12 ± 0.16), but figures changed when it was expressed in Body Lengths.s − 1 (h 2 = 0.55 ± 0.08, r A = − 0.10 ± 0.19 with cortisol and r A = − 0.64 ± 0.07 with body weight, respectively). Cortisol was moderately negatively correlated with body weight (r A = − 0.36 ± 0.18). The four lines did not differ for cortisol or U max , but when U max was expressed in BL.s − 1 it tended to be lower in the two selected lines — which were also significantly larger. However, this is likely due to a phenotypic decrease of relative U max with increasing body size. We conclude that selection for growth and/or domestication should not impact maximum sustained swimming speed in the European sea bass, but may tend to favour animals with low cortisol responsiveness. These traits could be used to orientate functional capabilities other than productivity in sea bass. Statement of relevance We estimate heritability of cortisol stress response and (for the first time) in European sea bass, as well as their correlations with growth. We show moderate correlations, and no correlated response to selection for growth. We also provide methods to evaluate these traits on large number of fishes. This can be useful to monitor and design breeding programmes.

To understand the genetic basis of coping style in European seabass, fish from a full factorial mating (10 females x 50 males) were reared in common garden and individually tagged. Individuals coping style was characterized through behavior tests at four different ages, categorizing fish into proactive or reactive: a hypoxia avoidance test (at 255 days post hatching, dph) and 3 risk-taking tests (at 276, 286 and 304 dph). We observed significant heritability of the coping style, higher for the average of risk-taking scores (h2 = 0.45 ± 0.14) than for the hypoxia avoidance test (h2 = 0.19 ± 0.10). The genetic correlations between the three risk-taking scores were very high (rA = 0.96-0.99) showing that although their repeatability was moderately high (rP = 0.64-0.72), successive risk-taking tests evaluated the same genetic variation. A mild genetic correlation between the results of the hypoxia avoidance test and the average of risk-taking scores (0.45 ± 0.27) suggested that hypoxia avoidance and risk-taking tests do not address exactly the same behavioral and physiological responses. Genetic correlations between weight and risk taking traits showed negative values whatever the test used in our population i.e. reactive individual weights were larger. The results of this quantitative genetic analysis suggest a potential for the development of selection programs based on coping styles that could increase seabass welfare without altering growth performances. Overall, it also contributes to a better understanding of the origin and the significance of individual behavioral differences.

Chantier qualité GA; Skeletal deformities are important traits for aqua-culture as they induce slow growing and low market value. We studied their genetic determinism and their interactions with the environment at the ongrowing stage in 5839 European sea bass from a partial factorial mating of 33 sires and 23 dams, reared in four sites. All families were mixed, and fish were first reared in one site (site B) until 35 g mean weight, then distributed to the four sites. A posteriori reconstruction of pedigree with microsatellites was used. Deformities were scored internally at slaughtering, and externally from photographs. Site B, where all fish were initially stocked until 35 g and exposed to forced swimming because of fast water current showed the highest rate of deformities with 83% and 65% from internal and external scoring respectively. Heritability on the underlying scale wash 2 =0.25±0.03 across all sites, and varied little between sites, while genetic correlations of deformities between sites were always high (>0.85). Genetic correlations between deformities and daily growth coefficient were variable between sites(rA=0.50±0.09, 0.43±0.10, 0.32±0.10, 0.18±0.10 for sites A, B, C, D respectively) and were positively linked with the average growth rate in each site. These results pointed out that there could be a relation between growth rate and the evolution of deformities at the grow-out stage.

This preliminary study assessed genotype _ diet interaction in late growth of European sea bass (Dicentrarchus labrax) fed with either a ￠sh meal (FM)- or a ￠sh oil (FO)-based diet (M) or an all-plant-based (PB) diet. Atotal of 550 ￠sh from 224 families were reared together and tagged. DNAwas sampled and microsatellites were used to assign parentage. When ￠sh weight was 192 _ 54 g, two tanks were fed with M (FM: 100%; FO: 100%) and two others with PB (FM: 0% and FO: 0%). Body weight (BW), fork length (FL) and ￠llet lipid content (CorrFat) were analysed with a linear model and with REML methodology.We observed no signi￠cant di!erences between groups, but a slightly lower (P50.03) daily growth coe⁄cient in sea bass fed PB than in those fed M. Heritability estimates of BWdi!ered signi￠cantly from zero (PB: 0.37 _ 0.18; M: 0.47 _ 0.24). Sire _ diet interactions were signi￠cant and genetic correlations ranged between 0.51 and 0.87, showing genotype _ diet interaction for BWand CorrFat. For the ￠rst time, genetic parameters in the context of total replacement of marine ￠shery by-products were estimated in European sea bass, showing re-ranking of family performances with extremely contrasted diets.

Among other strategies to improve fish welfare in rearing environment, domestication and/or selective breeding was proposed to minimize fish responsiveness to husbandry practices. To verify this hypothesis on a recently domesticated specie, the sea bass, Dicentrarchus labrax, L., an experiment was realized, using four populations differing according to their level of domestication or selection: one population produced from wild parents (Wild), one population produced from parents domesticated for one generation (Domesticated) and two produced from parents selected for growth for one generation (Selected A and Selected B). The experiment was carried out over 91 days with 600 fish (50 fish per tank, 150 fish per population). After a control period, the fish were submitted from day 35 and during 56 days to a stress treatment including frequent and random application of 4 acute stressors (pursuing fish with a net during 1 min, switching off the light for 2 s during the day or, conversely, switching on the light for 2 s during the night, and overflying a bird predator silhouette above the tank during 30 s). The two variables that were measured, i.e.: fish self-feeding behavior and growth performance [at days (D) 14, 35, 63, and 91] were both altered, albeit differentially according to populations, by the stress treatment. During the first stress period (from D35 to D63), all groups modified their feeding rhythm and highly increased their feed intake while their growth rate decreased (Domesticated and both Selected fish groups) or remained stable (Wild). During the second stress period (from D64 to D91) fish continued to modify their feeding rhythm (being more and more diurnal) and increased again their feed intake; conversely to what happened during the first stress period, here, these modifications were associated with an improvement of the growth rate of all populations. During the whole experiment, both Selected groups and Domesticated fish were always characterized by a higher body mass, specific growth rate and body condition factor than Wild fish. In conclusion, and according to the results of this study, a first generation of domestication or selection improved fish growth performance but, at this early stage do not modify behavioral responses to repeated acute stress exposure. (C) 2010 Elsevier B.V. All rights reserved.

Selective breeding to improve residual feed intake (RFI) in sea bass (Dicentrarchus labrax) is a major goal that would optimize economic gain while minimizing the environmental impact of production. Due to the difficulty in accurately measuring individual feed intake, no selective breeding program has yet been started. In a previous study, we identified a criterion phenotypically related to RFI variations: the loss of weight during feed deprivation, FD. Moreover, an additional composite criterion (CC) integrating both FD and weight gain during subsequent re-feeding (RF) was closely related to RFI, even though the relationship was only close to significance (P = 0.06). The aim of the present study was to estimate the heritability of these two traits, in order to complete the analysis of their pertinence as indirect criteria for use in a selective breeding program to improve RFI. We set up a full factorial mating design combining 41 sires and eight dams to produce mixed families offspring, which were all raised in the same tank. At 50 g, 1300 individuals were individually tagged and a fin clip was sampled for DNA extraction and parentage reassignment using five to six microsatellite loci, which showed they originated from 261 families. The evolution of individual body weight was recorded during a growth period of three weeks, followed by successive periods of three weeks feed deprivation and three weeks ad libitum re-feeding, repeated twice. Phenotypic and genetic correlations between the two feed deprivation periods or the two re-feeding periods were moderate (r = 0.45–0.51, and 0.71–0.73 respectively for phenotypic and genetic correlations) indicating that FD and RF are relatively repeatable. FD, RF and CC heritabilities were of the same magnitude (0.23 ± 0.04, 0.19 ± 0.04 and 0.22 ± 0.04, respectively), and sufficient to consider the use of such criteria in a future breeding program.

No commercial breeding programs have yet started to improve feed utilization efficiency in fish, mainly because of the difficulty in accurately measuring individual feed intake in fish reared in groups. Our general goal is to propose indirect criteria to be used for breeding of commercial lines. In a previous study undertaken with rainbow trout clones, a genetic correlation was detected between residual feed intake (RFI), and body weight variation during successive periods of feed deprivation (FD) and re-feeding (RF). To assess the pertinence of such indirect criteria for future breeding programs, we set up a large experiment using sea bass (Dicentrachus labrax), a recently domesticated species with broad genetic diversity. The objectives of the present study were to analyze the relationship of FD and RF with RFI, and to assess the consistency of such indirect criteria over time and their correlation with carcass quality. Fish originating from a full factorial design combining eight dams and 41 sires, were raised in the same tank. At 306 days post fertilization 2000 fish were individually tagged and their body weight recorded over a growth period of three weeks, followed by two successive periods of three weeks of feed deprivation and three weeks of ad libitum re-feeding. Fish performances were then classified, FD−, FD+, RF− and RF+ for fish exhibiting loss (FD) or gain (RF) of weight relatively lower (−) and higher (+) than the population mean. Fish were sorted into four groups (FD−/RF−, FD+/RF+, FD−/RF+, FD+/RF). Each of the 4 groups was split between three replicated tanks of 50 fish. Body weight gain and feed intake were measured for each replicate every three weeks over a six months period to estimate residual feed intake. The fish then underwent a period of three weeks of feed deprivation followed by a period of three weeks of ad libitum re-feeding. At the end of each period, individual weight gain variations were recorded, as well as muscle fat using ultrasonic measurement. The relationship with RFI variations was high for FD (P = 0.04, n = 12), and close to significance for a criterion merging FD and RF performances (P = 0.06, n = 12). FD but not RF was negatively correlated with muscle fat (P < 0.05, n = 600). In conclusion, selecting fish losing less weight during a three week feed deprivation period should lead to improve RFI, but also to increase muscle fatness. Using a combination of FD and RF as indirect criteria would result in slower progress in RFI, but would not impact carcass quality traits. The next step for inferring the potential genetic gain that can be expected is to assess the heritability of such criteria.

Malformations in farmed fish are a prime research topic as it has a major impact on fish welfare and on the economical value of the product. In this study, the genetic component of spine deformities was estimated in European sea bass, a major species of Mediterranean aquaculture, with the use of a posteriori reconstruction of pedigree with microsatellites. Our population exhibited a very high malformation rate (81%),probably due to intense swimming of fish during pre-growing The heritability of global spine deformities was evaluated to be 0.21 +/- 0.04 on the underlying scale (033 +/- 0.06 for lordosis, 0.13 +/- 0.04 for scoliosis). Deformities scored by an internal or external examination turned out to be genetically the same trait (genetic correlations>0.9), although phenotypic correlations were moderate to high (0.45 +/- 0.04 to 0.92 +/- 0.01) due to difficulties in scoring the less severe deformities. Along time (from 100 to 800 g mean weight), lordosis had a constant heritability, with very high genetic correlations between stages (>0.9). its incidence increased from 39 to 53% indicating that the malformation was probably present from the beginning of the rearing period but that its expression increased overtime. A positive linkage between spine deformities and growth rate was demonstrated both by the higher early weight of affected fish and by the positive genetic correlation between weight and malformation (from 0.21 +/- 0.15 to 0.40 +/- 0.14), although deformities have a negative phenotypic impact on growth. However, heritabilities of malformation traits calculated here are only estimates that may indirectly describe the sensitivity of fish to the particular pre-growing environment as a function of different body weight genotypes. A quantification of realised heritability would therefore be necessary before concluding on the existence of a genetic basis for spinal malformations such as lordosis and scoliosis. Nevertheless and by precaution, selection for fast growth rate needs careful monitoring of deformities, and selection against malformations may counteract impacts of selection for fast growth. (c) 2009 Elsevier B.V. All rights reserved.

Chantier qualité GA; International audience; Sea bass is a major species in Mediterranean aquaculture, but has a distribution area ranging from North Atlantic to South Mediterranean, with a population structure previously revealed by population genetics. To test the farming performances of wild sea bass populations, we produced a partial diallel cross mating scheme, using sires originating from North Atlantic (NAT), South Atlantic (SAT), West Mediterranean (WEM), North-East Mediterranean (NEM) and South-East Mediterranean (SEM). Fifteen sires per origin were mated in a full-factorial design using artificial fertilization with 9 NAT dams and 17 WEM dams, producing 10 population crosses and 1950 potential full-sib families. All fish were reared together, then tagged at an average weight of 20 g and distributed to four different sites (1800 fish per site). They were grown to an objective of 200 g mean weight, where 737 to 775 fish were slaughtered in each site, and their parentage was recovered using 6 to 7 microsatellite loci, resulting in 98.9% unique assignments. All populations had similar growth rates until tagging size (20 g), but differences appeared later on. No heterosis appeared for growth rate, and genotype by environment interaction (G × E) at the population level was limited, with a significant re-ranking only in one rearing site, while strong G × E for growth rate was observed within populations. Populations were different in shape, muscular fat content, and carcass yield, but not in fillet yield. In general, heterosis was absent and G × E was very limited between populations. No "ideal" population combining all favorable traits was identified. Differences between extreme populations ranged between 3 and 49% of the mean, depending on the traits. Interestingly, in almost all cases, these differences were within the reach of one generation of intense (5%) phenotypic selection.

Although individual electronic tagging using PIT (Passive Integrated Transponder) tags is well established, it is mainly used for fish > 60 mm in length. Since electronic tagging is an ideal identification method, we used RFID (Radio Frequency Identification) microtags (6 mm in length, 1 mm in diameter, 10 mg in mass) to characterize individual fish from the early stages of their development and throughout their lifecycles. We used sea bass, Dicentrarchus labrax (105 day-old fish weighing between 100 and 1100 mg), and studied the effects of intra-coelomic tagging in half the population using different endpoints including survival and tag reading, growth over 6 months and swimming responses. Dead fish were counted daily, biometric data were collected at 21 to 28 days intervals and fish were sexed at the end of the experiment. Behavioral swimming responses following a sudden dark challenge were evaluated after the first three biometric measurements (immediately after tagging, and then 21 and 42 days later). After 6 months, mean survival was 69%, the smallest surviving fish weighed 197 mg at tagging, and success in tag reading was 79% for the size class 300-400 mg after 63 days. No negative effects were observed on growth and most deaths occurred within 15 days after tagging with a first peak after 5 days but that did not particularly affect the smallest individuals. Differences in swimming responses were detected between tagged fish and untagged controls immediately after the surgical procedure with tagged fish swimming more than controls for 45 min. However, after 21 days, the tagged fish swam less than the untagged controls after being placed in the observation tank for 1 h and 45 min. At 42 days post-tagging, no further differences were observed. Overall, results suggested that the tagging method was suitable for fish as small as 400 mg and 36 mm in total length. This type of early tagging method is invaluable for the longitudinal monitoring of individual biological traits (e.g., growth) or for repeated assays with the same individual at distinct time points (e. g., behavior studies). We used it for a first evaluation of early growth differentiation between sexes and demonstrated a 31% mass gain difference in females that was visible as soon as the fish reached 105 days old. This confirms the potential of the method for the selection of early-expressed character traits which could lead to rearing cost savings for the aquaculture research field. (C) 2014 Elsevier B.V. All rights reserved.

Although food deprivation is a major ecological pressure in fishes, there is wide individual variation in tolerance of fasting, whose mechanistic bases are poorly understood. Two thousand individually tagged juvenile European sea bass were submitted to two 'fasting/feeding' cycles each comprising 3 weeks of food deprivation followed by 3 weeks of ad libitum feeding at 25 degrees C. Rates of mass loss during the two fasting periods were averaged for each individual to calculate a population mean. Extreme fasting tolerant (FT) and sensitive (FS) phenotypes were identified that were at least one and a half standard deviations, on opposing sides, from this mean. Respirometry was used to investigate two main hypotheses: (1) tolerance of food deprivation reflects lower mass-corrected routine metabolic rate (RMR) in FT phenotypes when fasting, and (2) tolerance reflects differences in substrate utilisation; FT phenotypes use relatively less proteins as metabolic fuels during fasting, measured as their ammonia quotient (AQ), the simultaneous ratio of ammonia excretion to RMR. There was no difference in mean RMR between FT and FS over 7 days fasting, being 6.70 +/- 0.24 mmol h(-1) fish(-1) (mean +/- s.e.m., N=18) versus 6.76 +/- 0.22 mmol h(-1) fish(-1) (N=17), respectively, when corrected to a body mass of 130 g. For any given RMR, however, the FT lost mass at a significantly lower rate than FS, overall 7-day average being 0.72 +/- 0.05 versus 0.90 +/- 0.05 g day(-1) fish(-1), respectively (P

International audience; Feed efficiency is a major goal for aquaculture sustainability, and selecting fish to genetically enhance this trait would be highly valuable. However, no selective breeding program specifically targeted to feed efficiency exists for farmed fish, mostly because of the difficulty of measuring individual feed intake. However, a negative phenotypic correlation between feed efficiency and weight loss at fasting has been previously demonstrated in sea bass submitted to feed deprivation (FD). We mated sea bass parents selected for their high (FD+) or low (FD-) weight loss at fasting to produce FD+ and FD- progeny, which were reared in a single tank to avoid common environmental effects. At 8 months of age, 1200 of those fish were submitted to three alternating periods of fasting (3 weeks) and re-feeding (3 weeks). Individuals were weighed at the end of each feeding and fasting period. Their line of origin was identified by genotyping of 12 microsatellite markers, resulting in 1130 unambiguously assigned fish (484 FD-, 686 FD+). FD- offspring lost significantly less weight than FD+ offspring in this feed deprivation trial. After that the feed efficiency of eight groups of 50 FD+ fish and eight groups of 50 FD- fish was evaluated in four successive 20-day periods. At the end of the fourth period, 10 fish per tank were sacrificed to evaluate their carcass yield. The FD- fish had a better overall growth and were fatter, and FD+ fish had a better carcass yield. A better feed efficiency was expected for the FD- fish, but differences between the two groups for this trait, measured either with feed efficiency ratio or with residual feed intake, were not consistently significant Although the two lines were clearly divergent for several traits, demonstration of feed efficiency differences between the FD+ and the FD- lines was not consistently observed in sea bass. A second generation of selection may allow further divergence in the lines and reveal differences in feed efficiency. (C) 2013 Elsevier B.V. All rights reserved.

The capacity of organisms to rapidly evolve in response to environmental changes is a key feature of evolution, and studying mutation compensation is a way to evaluate whether alternative routes of evolution are possible or not. Common carps (Cyprinus carpio) carrying a homozygous loss-of-function mutation for the scale cover genefgfr1a1, causing the ‘mirror’ reduced scale cover, were introduced in Madagascar a century ago. Here we show that carps in Malagasy natural waters are now predominantly covered with scales, though they still all carry the homozygous mutation. We also reveal that the number of scales in mutated carps is under strong polygenic genetic control, with a heritability of 0.49. As a whole, our results suggest that carps submitted to natural selection could evolve a wild-type-like scale cover in less than 40 generations from standing polygenic genetic variation, confirming similar findings mainly retrieved from model organisms.

Inter- and intraspecific crossbreeding experiments were conducted to evaluate the aquaculture potential of hybrids in the genus Dicentrarchus, focusing on fertilisation and hatching success. The experimental design consisted of 24 controlled crosses in which individual and pooled fertilisations were made between wild D. labrax individuals (8 dams and 5 sires originating from West Mediterranean and Atlantic populations) and wild D. punctatus (6 sires). Three experiments were successively performed: (1) dams from the Mediterranean population, individually considered to have good egg quality, (2) dams from Mediterranean population, individually considered to have poor egg quality and (3) crossbreeding using pooled eggs from the Atlantic population. In each case, batches of these eggs were fertilized by sperm from males of the two species. Sperm cell quality (concentration and motility) was verified before experimentation in all cases and equal numbers of sperm cells from each male were used to individually (without inter-sire competition) fertilise egg batches. Through the repeated artificial crosses between female common sea bass Dicentrarchus labrax (Linnaeus 1758) and male spotted sea bass D. punctatus (Block 1792), these experiments showed that no post-zygotic reproductive barriers exist to interspecific hybridisation between these two species when using D. labrax as dams and D. punctatus as sires. Phenotypically, the F1 hybrids were easily recognisable: they inherited the characteristic black spots of D. punctatus. Furthermore, embryo survival was significantly higher in interspecific crosses compared with intraspecific controls, showing increased fitness for this trait (increased performance at early life stage). Then, the experimental breeding design validates the observation that West Mediterranean and Atlantic common sea bass populations are different. Indeed, the inter-population crosses (between West Mediterranean dams and Atlantic sires) also revealed increased fitness at early life stages in comparison with the progeny of intra-Atlantic population crosses. However, these individuals were still smaller than their interspecific counterparts. The ability to produce viable F1 hybrids will have significant implications for the practical improvement of sea bass aquaculture.

WOS: 000280735200051, Two hundred fifty three full-sib families from 33 males and 23 females of European seabass were produced in a partly factorial mating design. All fish were reared in the same tank for 14 months until reaching mean weight of 35 g. then 7000 of them were individually tagged and weighed, and dispatched to four farms in different locations (France, Israel, Italy and Portugal) representing a wide variety of environmental conditions. Around mean weight of 400 g. 1177 to 1667 fish at each site were weighed. Daily growth coefficient (DGC) was calculated. Pedigrees were successfully redrawn for 99.2% of fish using microsatellite markers. Genetic correlations between sites were high for body weight (>0.80 in all cases but one, i.e., five cases over six), but only moderate for DGC (0.21-0.61), with one exception. This indicates significant G x E interactions for growth rate, which were not revealed when studying body weight due to shared common environment of the fish prior to separation to the different rearing environments. (C) 2010 Elsevier B.V. All rights reserved., ECEuropean Commission Joint Research CentreEuropean Community (EC) [Q5CR-2002-71720]; INRA and Ifremer, This work was carried out within the framework of CRAFT project no. Q5CR-2002-71720 (Heritabolum) funded by the EC and the private farms, Panittica Pugliese (Italy), Viveiro Villanova (Portugal) and Ardag (Israel), which are also thanked for their active participation. The present work was also part of the program of the Research Group 'Amelioration Genetique des Poissons' between INRA and Ifremer.

Selective breeding of European sea bass (Dicentrarchus labrax) receives a growing interest, as the estimated heritability of growth is medium to high. In this study, we compared the offspring of four groups of sea bass sires, mated with the same wild dams: wild (W), first generation of domestication (D), first generation of mass selection for length (M), first generation of PROSPER-like selection for length (P). The comparison was done both in replicated tanks (separate rearing) and in mixed tanks (mixed rearing) where sire origins were recovered by genotyping of eight microsatellite markers. Weight, length and growth rate were measured from day 238 post-fertilization (69 g mean weight) to day 611 post-fertilization (390 g mean weight). Both in mixed and separate tanks. both selected groups (P, M) were larger than unselected groups (W D). No difference was seen at any time between Wand D, nor between M and P. The selection response estimate on weight was larger in mixed tanks when compared to separate tanks (+42% in mixed tanks, +23% in separate tanks at day 611), yielding realized heritability estimates of 0.60 and 0.34, respectively, and confirming the excellent potential of the species for growth improvement through selective breeding. Both selection response and the amplification effect between mixed and separate tanks decreased as rearing density increased. Our hypothesis is that selection response is magnified by competition in mixed tanks, while suboptimal rearing conditions lower the observed selection response, more in separate tanks (where selected thus larger fish are at a higher density than unselected ones) than in mixed tanks (where all fish experience the same density effects). (c) 2008 Elsevier B.V. All rights reserved.

253 full-sib families from 33 males and 23 females of European seabass were produced in a partly factorial mating design. All fish were reared in the same tank during 14 months, then 7000 of them were dispatched in four farms to different locations (France, Israel, Italy, Portugal) representing a wide variety of environmental conditions. Around 400 g mean weight, 1177 to 1667 fish in each site were weighed and length was measured. Condition factor (K) was calculated. Pedigrees were redrawn a posteriori using microsatellites markers: parental origin could be retraced for 99.2% of fish. Due to a high incidence of deformities, the useful sample size was reduced to 491-670 fish per site. Maternal effects were small. Using a simple animal model, heritability of weight ranged from 0.38 +/- 0.14 to 0.44 +/- 0.14 in the different sites. Length was highly correlated to weight, with similar heritabilities. GxE interaction, estimated through genetic correlations of weight across the different environments ranged from 0.70 +/- 0.10 to 0.99 +/- 0.05. Genetic correlations between weight or length and K were not similar in the different sites. (c) 2008 Elsevier B.V. All rights reserved.

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The objective of this study was to develop a rapid and effective method of sexing juvenile sea bass with minimum labour and material.To this end, the gonad squash mount technique was applied along with macroscopic techniques for sexing a large number of experimental fish at the age of 215-275 days post fertilization (p.f.). At this age, 90% of the 3894 fish could be unambiguously sexed by macroscopic examination of their gonads, whereas the remaining proportion was identified using squash mount preparations (10%). The accuracy of the observations was measured up to classical histology procedures. Undifferentiated gonads accounted for 0.1% of the total population only.The application of the squashmount technique holds out the prospect of considerable improvement in the efficiency and rapidity of current sexing techniques in sea bass.

Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fgene.2018.00283/full#supplementary-material; International audience; Common carp is a major aquaculture species worldwide, commonly sold alive but also as processed headless carcass or filets. However, recording of processing yields is impossible on live breeding candidates, and alternatives for genetic improvement are either sib selection based on slaughtered fish, or indirect selection on correlated traits recorded in vivo. Morphological predictors that can be measured on live fish and that correlate with real slaughter yields hence remain a possible alternative. To quantify the power of morphological predictors for genetic improvement of yields, we estimated genetic parameters of slaughter yields and various predictors in 3-year-old common carp reared communally under semi-intensive pond conditions. The experimental stock was established by a partial factorial design of 20 dams and 40 sires, and 1553 progenies were assigned to their parents using 12 microsatellites. Slaughter yields were highly heritable (h2 = 0.46 for headless carcass yield, 0.50 for filet yield) and strongly genetically correlated with each other (rg = 0.96). To create morphological predictors, external (phenotypes, 2D digitization) and internal measurements (ultrasound imagery) were recorded and combined by multiple linear regression to predict slaughter yields. The accuracy of the phenotypic prediction was high for headless carcass yield (R2 = 0.63) and intermediate for filet yield (R2 = 0.49). Interestingly, heritability of predicted slaughter yields (0.48–0.63) was higher than that of the real yields to predict, and had high genetic correlations with the real yields (rg = 0.84–0.88). In addition, both predicted yields were highly phenotypically and genetically correlated with each other (0.95 for both), suggesting that using predicted headless carcass yield in a breeding program would be a good way to also improve filet yield. Besides, two individual predictors (P1 and P2) included in the prediction models and two simple internal measurements (E4 and E23) exhibited intermediate to high heritability estimates (h2 = 0.34 – 0.72) and significant genetic correlations to the slaughter yields (rg = |0.39 – 0.83|). The results show that there is a solid potential for genetic improvement of slaughter yields by selecting for predictor traits recorded on live breeding candidates of common carp.

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