National Institute of Aquatic Resources, Technical University of Denmark, DTU, Lyngby, Denmark.
Ifremer, Marine Environmental Science Laboratory UMR 6539, Plouzané, France.
PLoS One. 2018 Jun 13;13(6):e0198294. doi: 10.1371/journal.pone.0198294. eCollection 2018.
European eel (Anguilla anguilla) is a euryhaline species, that has adapted to cope with both, hyper- and hypo-osmotic environments. This study investigates the effect of salinity, from a morphological and molecular point of view on European eel larvae reared from 0 to 12 days post hatch (dph). Offspring reared in 36 practical salinity units (psu; control), were compared with larvae reared in six scenarios, where salinity was decreased on 0 or 3 dph and in rates of 1, 2 or 4 psu/day, towards iso-osmotic conditions. Results showed that several genes relating to osmoregulation (nkcc2α, nkcc2β, aqp1dup, aqpe), stress response (hsp70, hsp90), and thyroid metabolism (thrαA, thrαB, thrβB, dio1, dio2, dio3) were differentially expressed throughout larval development, while nkcc1α, nkcc2β, aqp3, aqp1dup, aqpe, hsp90, thrαA and dio3 showed lower expression in response to the salinity reduction. Moreover, larvae were able to keep energy metabolism related gene expression (atp6, cox1) at stable levels, irrespective of the salinity reduction. As such, when reducing salinity, an energy surplus associated to reduced osmoregulation demands and stress (lower nkcc, aqp and hsp expression), likely facilitated the observed increased survival, improved biometry and enhanced growth efficiency. Additionally, the salinity reduction decreased the amount of severe deformities such as spinal curvature and emaciation but also induced an edematous state of the larval heart, resulting in the most balanced mortality/deformity ratio when salinity was decreased on 3 dph and at 2 psu/day. However, the persistency of the pericardial edema and if or how it represents an obstacle in further larval development needs to be further clarified. In conclusion, this study clearly showed that salinity reduction regimes towards iso-osmotic conditions facilitated the European eel pre-leptocephalus development and revealed the existence of highly sensitive and regulated osmoregulation processes at such early life stage of this species.
欧洲鳗鲡（Anguilla anguilla）是一种广盐性物种，已经适应了高渗和低渗环境。本研究从形态学和分子学角度探讨了盐度对孵化后 0 至 12 天（dph）的欧洲鳗鲡幼鱼的影响。在 36 个实用盐度单位（psu；对照）中饲养的后代与在六个盐度条件下饲养的幼鱼进行了比较，在这六个条件下，盐度在 0 天或 3 天下降，下降速率为每天 1、2 或 4 psu，直至达到等渗条件。结果表明，在整个幼鱼发育过程中，有几个与渗透调节相关的基因（nkcc2α、nkcc2β、aqp1dup、aqpe）、应激反应（hsp70、hsp90）和甲状腺代谢（thrαA、thrαB、thrβB、dio1、dio2、dio3）表现出差异表达，而 nkcc1α、nkcc2β、aqp3、aqp1dup、aqpe、hsp90、thrαA 和 dio3 的表达在盐度降低时下降。此外，幼鱼能够保持与能量代谢相关的基因表达（atp6、cox1）稳定水平，而不受盐度降低的影响。因此，当盐度降低时，与降低的渗透调节需求和应激相关的能量过剩（nkcc、aqp 和 hsp 表达降低）可能促进了观察到的存活率提高、体型改善和生长效率提高。此外，盐度降低减少了严重畸形的数量，如脊柱弯曲和消瘦，但也导致幼鱼心脏水肿，当盐度在 3 天且以 2 psu/天时降低时，死亡率/畸形率达到最平衡的状态。然而，心包水肿的持续性以及它是否或如何成为该物种早期发育的障碍，需要进一步澄清。总之，本研究清楚地表明，向等渗条件降低盐度有助于欧洲鳗鲡前幼体的发育，并揭示了在该物种的早期生命阶段存在高度敏感和调节的渗透调节过程。
