Development of sex control techniques for European sea bass (Dicentrarchus labrax L.) aquaculture: effects of dietary 17a-methyIte stosterone prior to sex differentiation

  • Mercedes Blázquez
  • Francesc Piferrer
  • Silvia Zanuy
 et al. 
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Abstract

The purpose of this study was to develop a method for the hormonal masculinization of sea bass (Dicentrarchus labrax L.) reared under natural conditions of photoperiod and temperature. Sexually undifferentiated sea bass were fed 17a-methyltestosterone (MT) at 10 mg kg-¡ food during three distinct periods of 100 days each: Period 1, 126-226 days post fertilization (DPF) (July-November); Period 11,226-326 DPF (November-February); Period I1I, 326-426 DPF (February-May), and their combinations. Phenotypic sex ratios after hormone treatment were determined by histological examination of the gonads. MT significantly increased the proportion of juvenile males from controls (79%), to 93-100% in groups for which treatment included Period 1. In contrast, no significant alterations in the phenotypic sex ratio were observed when MT treatment started after this periodo In groups treated with MTfor more than 100 days, including Period 1,growth was significantly depressed. Furthermore, when MT was given for 300 days (126-426 DPF) , 7% of the fish were intersex. The effects of MT on the developing gonads were confirmed by a significant reduction of the gonadosomatic index (GSI) when treatment included Period I regardless of treatment duration. The visceral fat index (VFI) decreased with increasing durations of MT administration, denoting a lipolytic effect. However, 200 or more days after MT withdrawal, the mean VFI of MT-treated groups showed no differences with respect to that of the controls, indicating that the effects of MT on visceral fat mobilization were transitory. Similarly, reduction of the hepatosomatic index (HSI) and increase of the carcass index were found to be related to the length of MT administration, but values similar to those of control s were obtained after suppression of hormonal treatments. Survival of the treated groups was not compromised(average 76% vs. 78% in controls), and no teratologicalphenomena wereobserved.NotreatmentsstartingbeforePeriod1or of less than 100days of durationweretested in this study; however,theacquisitionof completeandfunctionalsex reversalwithoutanydeleterious effects after MT administrationduring this period and the lower effectivenessof MT treatmentin progressivelymoreadvancedstagesof development,showsthat Period 1is effectivefor the complete and permanent masculinizationof sea bass.

Author-supplied keywords

  • 17a-MethyItestosterone
  • Dicentrarchus labrax
  • Gonadal morphogenesis
  • Labile period
  • Masculinization
  • Sex steroids

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Authors

  • Mercedes Blázquez

  • Francesc Piferrer

  • Silvia Zanuy

  • Manuel Carrillo

  • Edward M Donaldson

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