References of "Mélard, Charles"
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See detailThermosensitivity of the sex differentiation process in the African catfish, Clarias gariepinus: Determination of the thermosensitive period
Santi, Saïdou ULg; Gennotte, Vincent ULg; Toguyeni, Aboubacar et al

in Aquaculture (2016), 455

Gonadal sex differentiation in gonochoristic fish is generally labile and under the control of two interacting processes: genetic sex determination (GSD) and environmental sex determination (ESD ... [more ▼]

Gonadal sex differentiation in gonochoristic fish is generally labile and under the control of two interacting processes: genetic sex determination (GSD) and environmental sex determination (ESD). Numerous experimental studies deal with temperature induced-sex differentiation in teleosts, but none focused on the African catfish Clarias gariepinus. The aim of this study was to confirm the thermosensitivity of the sex differentiation process and to determine the thermosensitive period during the African catfish development. Fish were exposed to high temperature (36 °C) for 3 days at different periods during ontogenesis. The treatment was applied every 3 days from fertilization until 29 days post-hatching (dph). Before and after the thermal treatment, fish were reared at 28 °C. Gonadal development was histologically characterized on fish sampled at 10, 15, 20, 25, 35, 45, 55 and 70 dph. Our results demonstrated that the African catfish displays a thermosensitivity of the sex differentiation process, with a masculinizing effect of high temperature (36 °C). The most thermosensitive period extended from 6 to 8 dph. Fish batches exposed to 36 °C during this period showed a sex-ratio skewed towards the male phenotype, ranging from 58 to 100% (high inter-familial variability). The African catfish gonads (male and female) stayed histologically undifferentiated until 20 dph. Obvious signs of gonadal differentiation clearly appeared at 25 dph in females and at 45 dph in males. Variability in sex-ratios between progenies and in the response to thermal treatment suggests a role of minor genetic factors and interactions between genomic and environmental determinants in the expression of the sexual phenotype. Statement of relevance: 1. This paper provides novel methods to control African catfish Clarias gariepinus sex differentiation through high temperature exposure and then to produce all-male populations. 2. Our work underlines the possibility to significantly reduce high temperature (masculinizing effect) treatment period to 3 days and consequently increase survival rate of progenies after treatment. 3. This study also shows the inter-family variability of thermosensitivity on the sex differentiation process in Clarias gariepinus. [less ▲]

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See detailEtude de la diversité génétique et de l’état des stocks des populations de barbeaux et de hotus en Wallonie. Amélioration des techniques d’élevage en vue de repeuplements raisonnés et de transferts de connaissances vers les pisciculteurs
Gennotte, Vincent ULg; Prignon, Christian ULg; Dierckx, Arnaud ULg et al

Report (2015)

Nase (Chondrostoma nasus) and common barbel (Barbus barbus) are two rheophilic cyprinid fish naturally present in South Belgian rivers. During the last decades, the construction of dams together with ... [more ▼]

Nase (Chondrostoma nasus) and common barbel (Barbus barbus) are two rheophilic cyprinid fish naturally present in South Belgian rivers. During the last decades, the construction of dams together with changes in hydrological regimes, modifications of riverbed morphology and water pollution caused some local dramatic declines in their populations. However, recent improvements in terms of water quality and habitat fragmentation allow now to implement a rational restocking plan of locally endangered patrimonial fish species such as nase and common barbel. To reach this goal, this project (co-funded by the European Fisheries Fund and the Wallonia Public Service) proposed to develop five complementary parts with specific objectives: • Review of the knowledge on nase and barbel geographical distribution and stock health in Wallonia. This section presents the distribution and recent evolution of populations in Europe, and more specifically in Wallonia. Areas where population declines were reported are identified. Even if a weak population expansion was reported in some isolated cases, the global status of Walloon populations is still concerning. • Characterization of genetic structure and diversity of South Belgium populations. Restocking operations for a conservation purpose have to be based on the knowledge and the use of wild type genetic strains. Nase and barbel populations from South Belgium were genetically characterized by use of microsatellites. Globally, nase and barbel populations are structured on a basin scale. A slight genetic differentiation exists between populations from the Rhine basin and the Meuse basin, defining two conservation units, but no finer structure was observed among populations from the Meuse basin. Genetic variation was high within populations. Genetic structure of barbel populations is more complex due to past restocking operations with different genetic lineages. An analysis of mDNA identified 6 different haplotypes but was unable to categorize them as autochtone or allochtone. • Development of fish production techniques. The complete control of fish farming is necessary to produce high quality juveniles for restocking. All the steps of the production cycle were addressed: broodstock management and reproduction, egg incubation, larval rearing and grow-out. Production systems ranging from extensive pond culture to intensive RAS were tested and the optimal farming conditions were identified (temperature, density, feeding, tank volumes, …). • Adaptation assessment of farmed fingerlings to natural conditions. Growth and survival performances of captive farmed fish were assessed in an experimental environment that mimics natural conditions. The results suggested that the more efficient practice for restocking would be based on operations performed in spring with large juveniles (3 to 50 g). • Know-how diffusion toward fish farmers. All the breeding and grow-out techniques developed for nase and barbel production are the subject of two handbooks. These documents, attached to the report, will be published and distributed to fish producers. [less ▲]

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See detailCulture Methods of Eurasian Perch and Yellow Perch Early Life Stages
Kestemont, Patrick; Mélard, Charles ULg; Held, J.A. et al

in Kestemont, Patrick; Summerfelt, Robert; Dabrowski, Konrad (Eds.) Biology and Culture of Percid Fishes (2015)

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See detailCulture Methods of Eurasian Perch During Ongrowing
Policar, Tomas; Samarin, A.M.; Mélard, Charles ULg

in Kestemont, Patrick; Summerfelt, Robert; Dabrowski, Konrad (Eds.) Biology and Culture of Percid Fishes (2015)

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See detailBrief exposure of embryos to steroids or aromatase inhibitor induces sex reversal in Nile tilapia (Oreochromis niloticus)
Gennotte, Vincent ULg; Mafwila Kinkela, Patrick; Ulysse, Bernard et al

in Journal of Experimental Zoology. Part A, Ecological Genetics and Physiology (2015), 323

This study aimed to develop sex reversal procedures targeting the embryonic period as tools to study the early steps of sex differentiation in Nile tilapia with XX, XY and YY sexual genotypes. XX eggs ... [more ▼]

This study aimed to develop sex reversal procedures targeting the embryonic period as tools to study the early steps of sex differentiation in Nile tilapia with XX, XY and YY sexual genotypes. XX eggs were exposed to masculinizing treatments with androgens (17α-methyltestosterone, 11-ketotestosterone) or aromatase inhibitor (Fadrozole), whereas XY and YY eggs were subjected to feminizing treatments with estrogen analog (17α-ethynylestradiol). All treatments consisted of a single or double 4-h immersion applied between 1 and 36 h post-fertilization (hpf). Concentrations of active substances were 1000 or 2000 µg l-1 in XX and XY, and 2000 or 6500 µg l-1 in YY. Masculinizing treatments of XX embryos achieved a maximal sex reversal rate of 10 % with an exposure at 24 hpf to 1000 µg l-1 of 11-ketotestosterone or to 2000 µg l-1 of Fadrozole. Feminization of XY embryos was more efficient and induced up to 91 % sex reversal with an exposure to 2000 µg l-1 of 17α-ethynylestradiol. Interestingly, similar treatments failed to reverse YY fish to females, suggesting either that a sex determinant linked to the Y chromosome prevents the female pathway when present in two copies, or that a gene present on the X chromosome is needed for the development of a female phenotype. [less ▲]

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See detailGenetic structure of nase, Chondrostoma nasus, and common barbel, Barbus barbus (Teleostei, Cyprinidae) populations in South Belgium rivers: toward a rational management of conservation restocking
Gennotte, Vincent ULg; Michaux, Johan ULg; Prignon, Christian ULg et al

Poster (2014, December)

Nase (Chondrostoma nasus) and common barbel (Barbus barbus) are two rheophilic cyprinid fish naturally present in the Belgian Meuse and Rhine basins. During the last decades, the construction of dams ... [more ▼]

Nase (Chondrostoma nasus) and common barbel (Barbus barbus) are two rheophilic cyprinid fish naturally present in the Belgian Meuse and Rhine basins. During the last decades, the construction of dams together with changes in hydrological regimes, modifications of riverbed morphology and water pollution have caused some local dramatic declines in their populations. However, recent improvements in terms of water quality and habitat fragmentation allow considering as realistic a rational restocking plan of locally endangered patrimonial fish species such as nase and common barbel. Restocking operations for a conservation purpose have to be based on the knowledge and the use of wild type genetic strains. Therefore, the aim of this study was to characterize the genetic structure and diversity of nase and common barbel populations in South Belgium rivers. Wild common barbels (n = 313) and nases (n = 271) were sampled by electrofishing in respectively 10 and 6 different tributaries from the Meuse and Rhine rivers. Genotyping was performed on 24 microsatellite markers for each species. Preliminary results showed, for both species, a differential genetic clustering between fish originating from the Meuse basin and those originating from the Rhine basin. Detailed analysis describing the genetic structure and diversity of South Belgium populations will be presented and will serve as a management tool to set up a breeding plan for conservation restocking. [less ▲]

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See detailSex determinism in Fish - the Belgian team case studies
Rougeot, Carole ULg; Gennotte, Vincent ULg; Santi, Saïdou ULg et al

Conference (2014, September 22)

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See detailThe sensitive period for male-to-female sex reversal begins at the embryonic stage in the Nile tilapia and is associated with the sexual genotype
Gennotte, Vincent ULg; Mélard, Charles ULg; D'Cotta, Helena et al

in Molecular Reproduction and Development (2014), 81

In this study, we sought to determine the mechanism of early sex reversal in a teleost by applying 4 hr feminization treatments to XY (17α-ethynylestradiol 2000 mg L-1) and YY (6500 mg L-1) Nile tilapia ... [more ▼]

In this study, we sought to determine the mechanism of early sex reversal in a teleost by applying 4 hr feminization treatments to XY (17α-ethynylestradiol 2000 mg L-1) and YY (6500 mg L-1) Nile tilapia embryos on the first day post-fertilization (dpf). We then searched for changes in the expression profiles of some sex-differentiating genes in the brain (cyp19a1b, foxl2, and amh) and in sex steroids (testosterone, 17β-estradiol, and 11-ketotestosterone) concentrations during embryogenesis and gonad differentiation. No sex reversal was observed in YY individuals, whereas sex reversal rates in XY progeny ranged from 0-60%. These results, together with the clearance profile of 17α-ethynylestradiol, confirmed the existence of an early sensitive period for sex determination that encompasses embryonic and larval development and is active prior to any sign of gonad differentiation. Estrogen treatment induced elevated expression of cyp19a1b and higher testosterone and 17β-estradiol concentrations at 4 dpf in both XY and YY individuals. foxl2 and amh were repressed at 4 dpf and their expression levels were not different between treated and control groups at 14 dpf, suggesting that foxl2 did not control cyp19a1b in the brains of tilapia embryos. Increased cyp19a1b expression in treated embryos could reflect early brain sexualization, although this difference alone cannot account for the observed sex reversal as the treatment was ineffective in YY individuals. The differential sensitivity of XY and YY genotypes to embryonic induced-feminization suggests that a sex determinant on the sex chromosomes, such as a Y repressor or an X activator, may influence sex reversal during the first steps of tilapia embryogenesis. [less ▲]

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See detailIMMUNE AND NEURO-ENDOCRINE RESPONSES OF GRAVID EURASIAN PERCH TO CHRONIC CONFINEMENT AND SOCIAL ISOLATION STRESS
Mandiki, SMN; Douxfils, Jessica; Massart, Sophie et al

Poster (2013, June)

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See detailLaboratory validation of a lateral flow device for the detection of CyHV-3 antigens in gill swabs
Vrancken, Robert; Boutier, Maxime ULg; Ronsmans, Maygane ULg et al

in Journal of Virological Methods (2013), 193

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See detailCortisol is responsible for positive and negative effects in the ovarian maturation induced by the exposure to acute stressors in Nile tilapia, Oreochromis niloticus
Gennotte, Vincent ULg; Sawadogo, Philippe; Milla, Sylvain et al

in Fish Physiology and Biochemistry (2012), 38

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See detailSperm quality analysis in XX, XY and YY males of the Nile tilapia (Oreochromis niloticus).
Gennotte, Vincent ULg; François, Ekniel; Rougeot, Carole ULg et al

in Theriogenology (2012)

In Nile tilapia (Oreochromis niloticus), individuals with atypical sexual genotype are commonly used in farming (use of YY males to produce all-male offsprings), but they also constitute major tools to ... [more ▼]

In Nile tilapia (Oreochromis niloticus), individuals with atypical sexual genotype are commonly used in farming (use of YY males to produce all-male offsprings), but they also constitute major tools to study sex determinism mechanisms. In other species, sexual genotype and sex reversal procedures affect different aspects of biology such as growth, behaviour and reproductive success. The aim of this study was to assess the influence of sexual genotype on sperm quality in Nile tilapia. Milt characteristics were compared in XX (sex-reversed), XY and YY males in terms of gonadosomatic index, sperm count, sperm motility and duration of sperm motility. Sperm motility was measured by computer-assisted sperm analysis (CASA) quantifying several parameters: total motility, progressive motility, curvilinear velocity, straight line velocity, average path velocity and linearity. None of the sperm trait measured differed significantly between the three genotypes. Mean values of gonadosomatic index, sperm concentration and sperm motility duration of XX, XY and YY males respectively ranged from 0.92 to 1.33 %, from 1.69 to 2.22 × 10(9) cells mL-1 and from 18’04’’ to 27’32’’. Mean values of total motility and curvilinear velocity 1 min after sperm activation respectively ranged from 53 to 58 % and from 71 to 76 µm s-1 for the three genotypes. After 3 min of activity, all the sperm motility and velocity parameters dropped by half and continued to slowly decrease thereafter. Seven min after activation, only 9 to 13 % of spermatozoa were still progressive. Our results prove that neither sexual genotype nor hormonal sex reversal treatments affect sperm quality in male Nile tilapias with atypical sexual genotype. [less ▲]

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See detailEffect of feeding regimes on growth and survival of Clarias gariepinus larvae: replacement of Artemia by a commercial feed
Vandecan, M.; Diallo, A.; Mélard, Charles ULg

in Aquaculture Research (2011), 42(5), 733-736

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See detailSkin mucus of Cyprinus carpio inhibits cyprinid herpesvirus 3 binding to epidermal cells
RAJ, Victor; Fournier, Guillaume ULg; Rakus, Krzysztof ULg et al

in Veterinary Research (2011), 42(92),

Detailed reference viewed: 89 (26 ULg)