Seawater carbonate chemistry and gamete quality and window of fertilisation in Atlantic cod

Impacts of global warming and CO2-related ocean acidification (OA) on fish reproduction may include chronic effects on gametogenesis and gamete quality, as well as acute effects on external fertilisation. Here, temperature thresholds and OA-sensitivity of gametogenesis and fertilisation were investigated in Atlantic cod, Gadus morhua. Three broodstock groups of farmed cod (FC 1-3) were exposed for three months to three maturation conditions (FC 1: Control, 6°C/400 μatm CO2; FC 2: Warming, 9.5°C/400 μatm; FC 3: Warming & OA, 9.5°C/1100 μatm). In addition, a broodstock group of wild cod (WC) was kept at control conditions to compare the acute temperature window of fertilisation with that of farmed cod (FC 1). Fertilisations were conducted in a temperature-gradient table at ten temperatures (between −1.5 and 12°C) and two CO2 levels (400/1100 μatm). In FC 1 and WC, fertilisation success was relatively high between 0.5°C and 11°C (TRange of ~10.5°C), indicating similar gamete quality in farmed and wild broodstocks kept at control conditions. Exposure of farmed broodstocks to warming (FC 2) and the combination of warming and OA (FC 3) impaired gamete quality, causing a reduction in fertilisation success of −20% (FC 2) and −42% (FC 3) compared to FC 1. The acute temperature window of fertilisation narrowed from FC 1 (TRange = 10.4°C) to FC 2 (TRange = 8.8°C) and FC 3 (TRange = 5.9°C). Acute effects of CO2 on fertilisation success were not significant. This study demonstrates potential climate change impacts on gametogenesis and fertilisation in Atlantic cod, suggesting the loss of spawning habitat in the coming decades.全球变暖与二氧化碳相关的海洋酸化（Ocean Acidification, OA）对鱼类繁殖的影响主要包括两类：一是对配子发生（gametogenesis）与配子质量（gamete quality）的慢性效应，二是对体外受精（external fertilisation）的急性效应。本研究以大西洋鳕（Gadus morhua）为实验对象，探究了其配子发生与受精过程的温度阈值及酸化敏感性。 本研究将3组养殖大西洋鳕亲鱼（broodstock，FC 1-3）分别置于3种成熟培育条件下暴露3个月：FC 1为对照组（6℃/400 μatm CO₂）；FC 2为升温组（9.5℃/400 μatm CO₂）；FC 3为升温与酸化联合组（9.5℃/1100 μatm CO₂）。此外，设置1组野生大西洋鳕亲鱼组（WC），置于对照条件下饲养，用于与养殖亲鱼组（FC 1）对比其受精的急性温度窗口。 受精实验采用温度梯度台，在-1.5℃至12℃区间内设置10个温度梯度，并设置2个二氧化碳水平（400/1100 μatm）开展。结果显示：FC 1与WC组的受精成功率在0.5℃至11℃区间内均维持较高水平（温度跨度约10.5℃），表明在对照条件下饲养的养殖与野生亲鱼，其配子质量无显著差异。 养殖亲鱼经升温暴露（FC 2）以及升温与酸化联合暴露（FC 3）后，配子质量受损，相较于FC 1组，受精成功率分别下降20%（FC 2）与42%（FC 3）。受精的急性温度窗口从FC 1组的10.4℃逐步缩减至FC 2组的8.8℃与FC 3组的5.9℃。二氧化碳浓度对受精成功率的急性效应并不显著。 本研究证实了气候变化对大西洋鳕配子发生与受精过程的潜在影响，预示未来数十年间其产卵栖息地或将出现丧失。