水体低氧的早期暴露对青鳉(Oryzias latipes)后期的生长、性别比和繁殖能力的影响

水体低氧已是全球性生态问题,常以季节性、偶发性和昼夜间等不同形式存在于不同的水体中。长期低氧可影响鱼类正常的生长和繁殖,但鱼类早期生活阶段暴露于不同形式的低氧后,后期的生长和繁殖是否会受到不利影响,目前研究甚少。本研究在实验室模拟了连续低氧(2.8 mg·L~(-1)DO)(H1)、昼夜低氧(H2)和发生在胚胎器官形成时期的偶发性低氧(H3)等3种情景对青鳉胚胎的发育影响,评估了这一早期暴露对青鳉后期的生长、存活和繁殖的影响。我们发现,3种低氧方式都可以显著延长青鳉胚胎的孵化周期,引起胚胎卵黄囊吸收和鱼鳔发育异常;暴露结束120 d后,H1组青鳉成鱼的畸形率显著升高、存活率和生长速度都显著下降;H1、H2和H3组中成鱼的雌雄比都发生了改变,鱼群中以雄鱼为主,且产卵量和受精率都显著下降。结果表明,鱼类早期胚胎发育阶段所受到的低氧暴露可对后期生长和繁殖产生不利影响,对子代补充和种群稳定产生重要影响;鱼类关键发育期所经历的低氧事件,以及昼夜低氧事件所产生的生态后果不容忽视。

Early-life Exposure to Hypoxia Altered Growth, Sex Ratio, and Reproduction in Medaka (Oryzias latipes)

Hypoxia is amongst the most pressing global problem in aquatic system. Seasonal hypoxia, temporary hypoxia, and diel cycling hypoxia are the commonly occurring hypoxia in different water bodies. The long-term hypoxia can affect fish normal growth and reproduction, but few studies have been conducted to evaluate how early-life exposure to different types of moderate hypoxia impacts later life growth and reproduction in fish. In this study, three hypoxia (2.8 mg L^-1 dissolved oxygen, DO) scenarios including long-term and continuous hypoxia (H1), diel cycling hypoxia (H2), and temporary hypoxia (H3) were designed under laboratory condition to investigate the effects of hypoxia on embryonic development of medaka (Oryzias latipes), and to further evaluate effects of early-life exposure on adult fish growth, survival, and reproduction. The present study found that the three hypoxia exposure can cause abnormal development in swimming bladder inflation and yolk sac absorption of embryos. After hypoxia exposure for 120 dph, H1 early-life exposure increased the skeletal and swimming malformation, decreased the survival and growth rate in adult fish. Furthermore, the three hypoxia exposure scenarios all led to changes in sex ratios and produced a significantly higher male to female ratio in adult fish. Meanwhile, the reductions in egg release and fertilization success were observed in medaka F0 generation following early-life hypoxia exposure. Our present observations suggest that hypoxia exposure during embryonic development can result in adverse growth and reproduction in fish, thereby threaten the offspring recruitment and the sustainability of the natural population of fish. As a long-term response to hypoxia, the potentially ecological consequences caused from diel cycling hypoxia and temporary hypoxia should be paid more attention.