Laboratory of Physiology, Atmosphere and Ocean Research Institute, The University of Tokyo, Chiba, Japan.
International Coastal Research Center, Atmosphere and Ocean Research Institute, the University of Tokyo, Otsuchi, Iwate, Japan.
Comp Biochem Physiol A Mol Integr Physiol. 2019 Dec;238:110565. doi: 10.1016/j.cbpa.2019.110565. Epub 2019 Sep 4.
The freshwater (FW) life of chum salmon is short, as they migrate to the ocean soon after emergence from the substrate gravel of natal waters. The alevins achieve seawater (SW) acclimating ability at an early developmental stage and the details of smoltification are not clear. We examined the stage-dependent SW acclimating ability in chum salmon alevins and found a sharp increase in SW tolerance during development that resembles the physiological parr-smolt transformation seen in other salmonids. Perturbation of plasma Na after SW exposure was prominent from the hatched embryo stage to emerged alevins, but the plasma Na became highly stable and more resistant to perturbation soon after complete absorption of yolk. Marker gene expression for SW-ionocytes including Na/K-ATPase (NKA α1b), Na-K-Cl cotransporter 1a (NKCC1a), Na/H exchanger 3a (NHE3a), cystic fibrosis transmembrane conductance regulators (CFTR I and CFTR II) were all upregulated profoundly at the same stage when the alevins were challenged by SW, suggesting that the stability of plasma Na concentration was partly a result of elevated osmoregulatory capability. FW-ionocyte markers including NKA α1a and NHE3b were consistently downregulated independent of stage by SW exposure, suggesting that embryos at all stages respond to salinity challenge, but the increase in SW osmoregulatory capability is restricted to the developmental stage after emergence. We propose that the "smoltification period" is condensed and integrated into the early development of chum salmon, and our results can be extrapolated to the future studies on hormonal controls and developmental triggers for smoltification in salmonids.
太平洋鲑鱼的淡水（FW）生活期很短，它们在从出生地的砾石基质中孵化后不久就会迁徙到海洋。幼鲑在早期发育阶段就获得了海水（SW）适应能力，并且变态的细节尚不清楚。我们检查了幼鲑变态期的阶段依赖性 SW 适应能力，发现其在发育过程中对 SW 的耐受性急剧增加，这类似于其他鲑科鱼类的生理幼鱼-变态转变。从孵化的胚胎阶段到刚孵出的幼鲑，SW 暴露后对血浆 Na 的扰乱很明显，但在卵黄完全吸收后不久，血浆 Na 变得高度稳定且更能抵抗扰乱。包括 Na/K-ATP 酶（NKA α1b）、Na-K-Cl 共转运蛋白 1a（NKCC1a）、Na/H 交换器 3a（NHE3a）、囊性纤维化跨膜电导调节因子（CFTR I 和 CFTR II）在内的 SW-离子细胞标志物的表达在幼鲑受到 SW 挑战时都显著上调，这表明血浆 Na 浓度的稳定性部分是由于渗透压调节能力的提高。FW-离子细胞标志物，包括 NKA α1a 和 NHE3b，在 SW 暴露时无论阶段如何都持续下调，这表明所有阶段的胚胎都对盐度挑战有反应，但 SW 渗透压调节能力的增加仅限于刚孵出后的发育阶段。我们提出，“变态期”被浓缩并整合到太平洋鲑鱼的早期发育中，我们的结果可以推广到鲑科鱼类变态的激素控制和发育触发的未来研究。
