Table_2_Bacterial community structures and dynamics associated with rotated positioning syndrome in gilthead sea bream (Sparus aurata) larviculture.xlsx

IntroductionThe availability of high-quality gilthead seabream (Sparus aurata) larvae in larviculture represents a major bottleneck to the aquaculture. This challenge can be compounded by losses resulting from the emergence of a clinical disorder’s symptomatology. In this study, the observed syndrome included a rotated positioning of the larval sagittal plane and in most cases leading eventually to death.
MethodsHerein, we examined using amplicon sequencing of the 16S rDNA the bacterial communities associated with S. aurata larvae at different conditions (including both fish with no evidence of the syndrome and fish with syndrome) during the early developmental stages along with the contribution of rearing water, organic matter and provided feed in the microbiota during an experiment of 18 days.
ResultsOver the development of larvae, differences were observed in the bacterial composition between healthy and symptomatic larvae as well as between components of the system. A remarkable presence of members of the Psychrobacter genus was observed in symptomatic larvae with a significant increase at 18dph. The healthy larvae harbor different bacterial profile with a dominance of Vibrio and Bacillus genera during 3-8dph, various members of Alphaproteobacteria during 11-14dph and Marinifilum at 18dph. The rearing water showed a different bacterial profile compared to the other components, with a slight effect of healthy larvae at 3-8dph. The bacteriome of feeds provided during the rearing of larvae was found to be diverse. Chlorella was mainly dominated by members of Firmicutes, while Rotifer and Artemia were mainly dominated by members of Proteobacteria including different species of Psychrobacter. At 18dph, Artemia feed seems to affect the symptomatic larvae bacteriome, where it enhanced the presence of Psychrobacter spp.
DiscussionInterestingly, the comparative network analysis at 18dph indicated that the bacterial associations in symptomatic larvae were primarily driven by members of the Psychrobacter genus. While various phyla contributed to bacterial associations in healthy larvae with different frequencies including mainly members of Proteobacteria, Bacteroidota and Firmicutes phyla. Finally, the Gammaproteobacteria/Alphaproteobacteria ratio was found to be related to the health condition of larvae. This study provides valuable information which can be used as indicators for monitoring the health status of S. aurata larvae.

引言：在金头鲷（Sparus aurata）仔鱼培育过程中，优质仔鱼的稳定供应是水产养殖的核心瓶颈之一。临床病症引发的死亡损失会进一步加剧这一产业难题。本研究中观测到的综合征表现为仔鱼矢状面异常旋转，多数患病个体最终会死亡。

方法：本研究依托18天的养殖实验，采用16S核糖体DNA（16S rDNA）扩增子测序技术，分析了早期发育阶段不同状态（含无综合征症状的健康仔鱼与出现病症的患病仔鱼）的金头鲷仔鱼相关细菌群落，并同步探究了养殖水体、有机质与投喂饲料对养殖系统微生物群的贡献。

结果：在仔鱼发育进程中，健康仔鱼与患病仔鱼的细菌群落组成存在显著差异，养殖系统各组分间的细菌结构亦存在明显区分。患病仔鱼中存在大量嗜冷杆菌属（Psychrobacter）成员，且在孵化后18日龄（days post hatching，dph）其丰度显著升高。健康仔鱼则拥有独特的细菌群落结构：3~8日龄时以弧菌属（Vibrio）和芽孢杆菌属（Bacillus）为优势类群，11~14日龄时优势类群为α-变形菌纲（Alphaproteobacteria）各成员，18日龄时则以海丝菌属（Marinifilum）为主导。养殖水体的细菌群落结构与其他组分差异显著，仅在3~8日龄时受到健康仔鱼的轻微影响。各投喂饲料的细菌组成本身具有较高多样性：小球藻（Chlorella）主要以厚壁菌门（Firmicutes）成员为优势类群，轮虫（Rotifer）与卤虫（Artemia）则主要以变形菌门（Proteobacteria）成员为主，其中包含多种嗜冷杆菌属物种。在18日龄时，卤虫投喂似乎会影响患病仔鱼的细菌组，可提升嗜冷杆菌属物种的丰度。

讨论：值得注意的是，18日龄时的比较网络分析显示，患病仔鱼的细菌类群间关联主要由嗜冷杆菌属成员驱动；而健康仔鱼的细菌类群间关联则由多个菌门以不同频率共同参与，主要包括变形菌门、拟杆菌门（Bacteroidota）与厚壁菌门成员。此外，γ-变形菌纲（Gammaproteobacteria）与α-变形菌纲的丰度比值与仔鱼的健康状态显著相关。本研究获得的宝贵信息可作为监测金头鲷仔鱼健康状态的潜在指标。