Table 1_Egg quality markers in domesticated broodstock of Atlantic halibut (Hippoglossus hippoglossus) with relevance for optimization of hatchery protocols.xlsx

IntroductionCommercial production of Atlantic halibut (Hippoglossus hippoglossus) has many obstacles, such as low and highly variable egg quality and survival rates during early developmental stages. We re-evaluated commonly used egg quality markers of Atlantic halibut in 17 egg batches from 11 different females in 2019.
MethodsAt a commercial hatchery in Norway, abnormal phenotypes were observed for several developmental milestones. The parameters fertilization success, percentage of normal early blastomere morphology, percentage of normally developing embryos at blastopore closure, and survival prior to hatching were analyzed to identify egg quality indicators. Small-scale egg incubators were utilized to track eggs with abnormal early blastomere symmetry individually until hatching.
ResultsThe observed egg quality parameters varied between the egg groups, with an average of 62 ± 18% fertilization success (31–88%), 55 ± 23% survival until hatching (25–99%), and 49 ± 20% hatching success (22–85%). The percentage of normal early blastomeres, 69 ± 10% (51–85%) was not a significant predictor of hatching success in flask incubations but was a significant predictor in 96-well plate incubations. The development of individual eggs was followed in 96-well plates (n = 509), where eggs with normal early blastomere morphology had 83% higher hatching success than those with abnormal blastomeres (52% vs 22%). The percentage of normally developing embryos at blastopore closure 81 ± 18% (41–99%) was the strongest predictor overall and was significantly associated with both survival until hatching and hatching success.
DiscussionSurvival until hatching and the proportion of embryos with successful blastopore closure can both serve as egg quality indicators, offering potential enhancements to commercial hatchery management practices.

引言
大西洋庸鲽（Atlantic halibut，学名*Hippoglossus hippoglossus*）的商业化养殖面临诸多障碍，例如卵子质量偏低且波动幅度大，以及早期发育阶段的成活率极不稳定。本研究于2019年针对来自11尾不同雌鱼的17批卵子，重新评估了大西洋庸鲽常用的卵子质量标志物（egg quality markers）。

方法
本研究在挪威一家商业化育苗场开展，研究人员观察到多个发育节点存在异常表型。为筛选有效的卵子质量评价指标，本研究分析了多项参数：受精率、正常早期卵裂球（early blastomere）形态占比、胚孔闭合（blastopore closure）阶段正常发育胚胎占比，以及孵化前成活率。研究使用小型卵子孵化装置，对存在早期卵裂对称性异常的卵子进行单独跟踪，直至其孵化。

结果
不同批次卵子的各项卵子质量参数存在显著差异：受精率平均为62±18%（区间31%~88%），孵化前成活率平均为55±23%（区间25%~99%），孵化成功率平均为49±20%（区间22%~85%）。正常早期卵裂球占比平均为69±10%（区间51%~85%），该参数在烧瓶孵化体系中无法有效预测孵化成功率，但在96孔板（96-well plate）孵化体系中则为显著预测因子。研究在96孔板中对509枚单个卵子的发育过程进行跟踪，结果显示，具有正常早期卵裂球形态的卵子，其孵化成功率比卵裂球异常的卵子高出83%（前者为52%，后者为22%）。胚孔闭合阶段正常发育胚胎占比平均为81±18%（区间41%~99%），该参数是整体表现最优的预测因子，且与孵化前成活率及孵化成功率均存在显著相关性。

讨论
孵化前成活率与胚孔闭合正常的胚胎占比均可作为卵子质量评价指标，有望为商业化育苗场的管理实践提供优化方向。