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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 (in press)

In this study, we applied feminization treatments of 4 h on XY (17α-ethynylestradiol 2000 µg l-1) and YY (6500 µg l-1) Nile tilapia embryos on the first dpf. The mechanism of early sex reversal was ... [more ▼]

In this study, we applied feminization treatments of 4 h on XY (17α-ethynylestradiol 2000 µg l-1) and YY (6500 µg l-1) Nile tilapia embryos on the first dpf. The mechanism of early sex reversal was investigated by searching for changes in the expression profiles of some sex-differentiating genes in the brain (cyp19a1b, foxl2 and amh) and in sexual steroids (testosterone, 17β-estradiol and 11-ketotestosterone) concentrations during embryogenesis and gonad differentiation. No sex reversal was observed in YY but sex reversal rates in XY progenies ranged from 0 to 60 %. These results, together with the clearance profile of 17α-ethynylestradiol confirmed the existence of an early sensitive period for sex determination encompassing embryonic and larval development, prior to any sign of gonad differentiation. The estrogen treatment induced an increased expression of cyp19a1b and a higher level of testosterone and 17β-estradiol at 4 dpf in XY and YY. Foxl2 and amh were repressed at 4 dpf and expression levels were not different between treated and control groups at 14 dpf suggesting that foxl2 did not control cyp19a1b in the brain of tilapia embryos. Increased cyp19a1b expression in treated embryos could reflect a sign of early brain sexualization but alone cannot account for the sex reversal effect as the treatment was ineffective in YY. The differential sensitivity of XY and YY genotypes to embryo induced-feminization suggests that a sex determinant on the sex chromosomes, either a Y repressor or an X activator may influence the sex reversal during the first steps of tilapia embryogenesis. [less ▲]

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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 (in press)

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 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 detailBiologie de la reproduction et analyse du déterminisme et de la différenciation du sexe à des stades précoces chez le tilapia du Nil, Oreochromis niloticus
Gennotte, Vincent ULg

Doctoral thesis (2014)

La reproduction des poissons téléostéens se caractérise par une diversité des types de sexualité (gonochorisme vs hermaphrodisme) et des systèmes de déterminisme du sexe (génétique et/ou environnemental ... [more ▼]

La reproduction des poissons téléostéens se caractérise par une diversité des types de sexualité (gonochorisme vs hermaphrodisme) et des systèmes de déterminisme du sexe (génétique et/ou environnemental), ainsi que par une plasticité du contrôle génétique et endocrinien de la différenciation sexuelle incomparables parmi les autres vertébrés. Le tilapia du Nil (Oreochromis niloticus) est un cichlidé gonochorique possédant un système chromosomique de déterminisme sexuel à homogamétie femelle XX/XY, complété par un déterminisme environnemental, les hautes températures pouvant modifier le développement phénotypique du sexe. L’intérêt porté à cette espèce en aquaculture à conduit au développement de différentes techniques de contrôle du sexe (par traitement hormonal) permettant la production de poissons présentant différentes combinaisons de phénotype/génotype sexuels (mâles XX, XY, YY, femelles XX, XY et YY). Ces derniers constituent des outils majeurs de l’étude du déterminisme et de la différenciation du sexe et soulèvent de nombreuses questions concernant les interactions génotype/phénotype sexuels chez cette espèce. Au regard de ces considérations, nous nous sommes fixés 2 objectifs principaux : 1. Déterminer l’influence du génotype sexuel sur certains aspects liés à la biologie reproductive chez le tilapia du Nil tels que la qualité du sperme, les taux de stéroïdes sexuels (testostérone, T ; 17β-œstradiol, E2 ; 11-cétotestostérone, 11KT) et les comportements agressifs. Le génotype sexuel ne semble pas avoir d’influence sur la qualité gamétique des mâles, puisqu’aucune différence n’est observée entre les individus XX, XY et YY, alors que paradoxalement, les taux de 11KT sont plus élevés chez les mâles XX. De la même manière, les femelles présentent des taux croissants d’E2 chez les individus XX, XY et YY. Ces différences de taux de stéroïdes sexuels pourraient être liées aux taux d’agressivité (évalué par la quantification de huit comportements agonistiques dans des confrontations mâle-femelle) plus élevés des mâles XX et des femelles XY et YY et engendrer des perturbations des comportements reproducteurs. Des recherches complémentaires sont nécessaires d’une part, pour évaluer l’effet du génotype sur la qualité des gamètes des femelles et d’autre part, pour déterminer si les modifications phénotypiques observées sont liées à l’expression du génotype sexuel ou à des perturbations engendrées par les traitements hormonaux d’inversion sexuelle administrés durant la période de différenciation des gonades. 2. Explorer les mécanismes du déterminisme et de la différenciation à des stades précoces du développement. Grâce à la mise au point d’une technique d’inversion sexuelle ciblant les périodes embryonnaire et larvaire (avant 10 jpf) par des expositions courtes (4h) d’embryons âgés d’un jpf à des androgènes (11KT, 17α-méthyltestostérone), un inhibiteur de l’aromatase (Fadrozole) ou un œstrogène (17α-éthynylœstradiol), nous avons confirmé l’existence d’une période sensible de la différenciation sexuelle avant le développement des gonades. Les voies de différenciation phénotypique semblent être différentes en fonction du génotype, puisque la masculinisation des embryons XX est moins efficace (max 10%) que la féminisation d’embryons XY (max 91%). De la même manière, un probable effet chromosomique rend inefficace la féminisation d’embryons YY. La féminisation des individus XY est concomitante avec une augmentation des taux de T et d’E2 et d’expression de l’aromatase cérébrale à 4 jpf qui pourrait indiquer un rôle précoce du cerveau dans la différenciation sexuelle. Dans l’ensemble, nos résultats nous permettent de suggérer, d’une part, que les premiers événements moléculaires de la différenciation sexuelle du tilapia sont initiés avant la formation des gonades, et d’autre part, que chez les individus sexuellement inversés, des différences sexuelles peuvent apparaître dans le cerveau avant ou en même temps que le développement des gonades et induire des modifications comportementales à l’âge adulte. La question du rôle possible du cerveau dans la différenciation des gonades reste ouverte. [less ▲]

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See detailBehaviours Associated with Acoustic Communication in Nile Tilapia (Oreochromis niloticus)
Longrie, Nicolas; Poncin, Pascal ULg; Denoël, Mathieu ULg et al

in PLoS ONE (2013), 8(4), 61467

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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 detailOntogeny of swimming movements in the catfish Clarias gariepinus
Mauguit, Quentin ULg; Gennotte, Vincent ULg; Becco, Christophe ULg et al

in The Open Fish Science Journal (2010), 3

The swimming movements of C. gariepinus larvae were recorded with a high-speed camera (400, 500 and 800 fps) from 0 to 336 hours post-hatching. Movements of adult fish were also recorded to provide ... [more ▼]

The swimming movements of C. gariepinus larvae were recorded with a high-speed camera (400, 500 and 800 fps) from 0 to 336 hours post-hatching. Movements of adult fish were also recorded to provide information on the last developmental stage. Seven landmarks positioned on the fish midline were used during tail beating to determine various parameters during ontogeny and, on the basis of these parameters, to describe the first appearance of swimming movements and their development and efficiency during growth. Larvae were unable to swim at hatching (4 mm total length). Swimming movements were established at 48 hours posthatching when the fish measured between 7 and 8 mm total length and the yolk sac was more than 95% absorbed. At this stage, lateral excursion of the head appeared strongly reduced (from 13% to 6% of the total length). The efficiency of swimming movements increased throughout ontogeny, as did the homogeneity of the speed of the propulsive wave. Spontaneous swimming speed of 1 to 10 TLs-1 were observed in early stage (8-12 hPH). The various speed induced significant variations in parameters such as the amplitude of lateral head movements, swimming efficiency, and body rigidity. No major change was observed at the theoretical flow-regime transition. [less ▲]

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See detailEarly sex reversal during the embryonic development in the Nile tilapia
Rougeot, Carole ULg; Kanfitine, Samane, Yadja; Prignon, Christian ULg et al

in Cybium (2008), 32(2), 104-105

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See detailCannibalism in Anchovy (Engraulis encrasicolus) in the North Aegean Sea (Greece)
Gennotte, Vincent ULg; Torre, Michele; Kallianiotis, Argyris

Poster (2007)

Egg and larval cannibalism was characterized in the European anchovy (Engraulis encrasicolus) during the spawning season in the North Aegean Sea. About 3 % of the sampled fish had consumed eggs and 7 ... [more ▼]

Egg and larval cannibalism was characterized in the European anchovy (Engraulis encrasicolus) during the spawning season in the North Aegean Sea. About 3 % of the sampled fish had consumed eggs and 7 % larvae. Egg consumption was observed during the night and larval consumption during the day. Cannibalism seems to be an opportunistic feeding strategy of anchovy, depending on prey availability and proximity of adults, larvae and eggs in relation with the diel vertical migrations of the fish. [less ▲]

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See detailCharacterization of the primary sonic muscles in Carapus acus (Carapidae): a multidisciplinary approach
Parmentier, Eric ULg; Gennotte, Vincent ULg; Focant, Bruno et al

in Proceedings of the Royal Society B : Biological Sciences (2003), 270(1530), 2301-2308

Sound production in carapid fishes results from the action of extrinsic muscles that insert into the swim bladder. Biochemical, histochemical and morphological techniques were used to examine the sonic ... [more ▼]

Sound production in carapid fishes results from the action of extrinsic muscles that insert into the swim bladder. Biochemical, histochemical and morphological techniques were used to examine the sonic muscles and compare them with epaxial muscles in Carapus acus. Sonic fibres are thicker than red and thinner than white epaxial fibres, and sonic fibres and myofibrils exhibit an unusual helicoidal organization: the myofibrils of the centre are in a straight line whereas they are more and more twisted towards the periphery. Sonic muscles have both features of red (numerous mitochondria, high glycogen content) and white (alkali-stable ATPase) fibres. They differ also in the isoforms of the light chain (LC3) and heavy chain (HC), in having T tubules at both the Z-line and the A–I junction and in a unique parvalbumin isoform (PAI) that may aid relaxation. All these features lead to the expression of two assumptions about sound generation: the sonic muscle should be able to perform fast and powerful contractions that provoke the forward movement of the forepart of the swim bladder and the stretching and ‘flapping’ of the swim bladder fenestra; the helicoidal organization allows progressive drawing of the swim bladder fenestra which emits a sound when rapidly released in a spring-like manner. [less ▲]

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See detailProduction de sons chez les Carapidae : approche multidisciplinaire
Parmentier, Eric ULg; Gennotte, Vincent ULg; Lagardère, Jean-Paul

Conference (2003)

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