Sexual differentiation and juvenile intersexuality in the European sea bass (Dicentrarchus labrax)

Authors

  • Eric Saillant,

    Corresponding author
    1. IFREMER, Laboratoire de Recherche en Pisciculture Marine (LRPM), Chemin de Maguelonne, 34250, Palavas-les-Flots, France
    2. Ecloserie Marine de Gravelines, Voie des Enrochements, 59820, Gravelines, France
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  • Béatrice Chatain,

    1. IFREMER, Laboratoire de Recherche en Pisciculture Marine (LRPM), Chemin de Maguelonne, 34250, Palavas-les-Flots, France
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  • Bruno Menu,

    1. IFREMER, Laboratoire de Recherche en Pisciculture Marine (LRPM), Chemin de Maguelonne, 34250, Palavas-les-Flots, France
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  • Christian Fauvel,

    1. IFREMER, Laboratoire de Recherche en Pisciculture Marine (LRPM), Chemin de Maguelonne, 34250, Palavas-les-Flots, France
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  • Marie Odile Vidal,

    1. IFREMER, Laboratoire de Recherche en Pisciculture Marine (LRPM), Chemin de Maguelonne, 34250, Palavas-les-Flots, France
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  • Alexis Fostier

    1. INRA, Station Commune de Recherche en Ichtyologie Biodiversité et Environnement (SCRIBE), Campus de Beaulieu, Avenue Général Leclerc, 35042, Rennes, France
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*All correspondence to current address: Eric Saillant, Department of Wildlife and Fisheries Sciences, TAMU 2258, Texas A&M University, College Station, TX 77843–2258, U.S.A. E-mail: esaillant@wfscgate.tamu.edu

Abstract

Sexual differentiation was studied at the histological level using a mixture of 30 families of sea bass Dicentrarchus labrax. Most of the fish (93%) differentiated into males as usually observed in farmed populations. All testes were differentiated when the males reached 12 cm and no more undifferentiated fish were found from 419 days post-fertilization (p.f.). In 28% of the males, among the biggest, sexual differentiation had already begun at 168 days p.f. (8.3–9.5 cm) and these fish started spermatogenesis in their first year of life. The other males differentiated later and remained immature at the end of their first year of life. Ovaries could be identified at the histological level from the age of 168 days p.f. (7.9–9.0 cm) and the females became significantly longer than the males from the age of 191 days p.f., i.e. during the process of ovarian differentiation. In the studied group, 62% of the males developed intratesticular oocytes. Such intersexuality had no consequence on growth rate. Intratesticular oocytes were also recorded in testes of wild males originating from Atlantic (Britain and Gulf of Gascogne) and West Mediterranean showing that juvenile intersexuality is not restricted to farmed populations but is a widespread phenomenon in sea bass.

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