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<p>The increasing production of hybrid groupers in offshore net pen farming systems has raised concerns regarding genetic contamination from escaping individuals. Triploidy induction is a promising technique to mitigate this risk by inhibiting gonadal development and reproduction. Although triploidy induction techniques are well established for various fish species, research on groupers and its closely related species remains limited. Here, we aimed to address the risk of genetic contamination posed by farmed hybrid groupers in Japan by examining nuclear behaviour in fertilised <i>Kue-Tama</i> (<i>Epinephelus bruneus</i> × <i>Epinephelus lanceolatus</i>; KT) eggs. We induced triploidy in KT and determined the optimal cold shock (CS) treatment conditions. Cytological observations of KT eggs fertilised with <i>E. lanceolatus</i> sperm showed that meiosis II progressed from metaphase to anaphase within 4&#xa0;min post-fertilisation (mpf), with a second polar body extrusion occurring at 10 mpf. Accordingly, CS treatment at 8&#xa0;°C was applied at 5 mpf for 10, 15, or 20&#xa0;min. The 15- and 20-min treatments yielded high triploidy induction rates of 95.8 and 97.9%, respectively. However, the same protocol applied at a larger scale using a larger treatment container decreased the triploidy rate by 30.1%. Histological analysis of 555-day-old triploid KT revealed no primary growth stage oocytes, suggesting functional sterility. We demonstrate the feasibility of triploidy induction in KT and provide insights into its sterility and potential as a genetic containment strategy. Our findings offer a foundation for the further optimisation of CS protocols for commercial-scale applications and contribute to the sustainable development of grouper aquaculture.</p>

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Triploidy induction and gonadal maturation in F1 and backcross hybrids of Epinephelus bruneus and Epinephelus lanceolatus

  • 期刊论文

  • 发表日期：

    2025年7月8日

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  • Ryuichiro Aoki,
  • Toru Kobayashi,
  • Kosuke Kawai,
  • Shukei Masuma

摘要

The increasing production of hybrid groupers in offshore net pen farming systems has raised concerns regarding genetic contamination from escaping individuals. Triploidy induction is a promising technique to mitigate this risk by inhibiting gonadal development and reproduction. Although triploidy induction techniques are well established for various fish species, research on groupers and its closely related species remains limited. Here, we aimed to address the risk of genetic contamination posed by farmed hybrid groupers in Japan by examining nuclear behaviour in fertilised Kue-Tama (Epinephelus bruneus × Epinephelus lanceolatus; KT) eggs. We induced triploidy in KT and determined the optimal cold shock (CS) treatment conditions. Cytological observations of KT eggs fertilised with E. lanceolatus sperm showed that meiosis II progressed from metaphase to anaphase within 4 min post-fertilisation (mpf), with a second polar body extrusion occurring at 10 mpf. Accordingly, CS treatment at 8 °C was applied at 5 mpf for 10, 15, or 20 min. The 15- and 20-min treatments yielded high triploidy induction rates of 95.8 and 97.9%, respectively. However, the same protocol applied at a larger scale using a larger treatment container decreased the triploidy rate by 30.1%. Histological analysis of 555-day-old triploid KT revealed no primary growth stage oocytes, suggesting functional sterility. We demonstrate the feasibility of triploidy induction in KT and provide insights into its sterility and potential as a genetic containment strategy. Our findings offer a foundation for the further optimisation of CS protocols for commercial-scale applications and contribute to the sustainable development of grouper aquaculture.