Pink salmon hatch in fresh water, but their highly anadromous life history requires them to migrate into the ocean immediately after gravel-emergence, at a very small size. During their down-river migration these larvae undergo rapid smoltification that completely remodels their osmoregulatory physiology. At this time, the larvae reportedly have high whole-body Na + contents and we hypothesised that the active accumulation of internal Na + occurs in preparation for ocean entry. Using a comparative approach, the present study characterised the ontogeny of Na + regulation in larvae of the anadromous pink salmon and the fresh-water rainbow trout. Our results indicate that larvae from both species actively accumulated Na + ; however, whole-body Na + content was higher in rainbow trout larvae compared to pink salmon. The time-course of this response was similar in the two species, with highest Na + -uptake rates ( $$J^{{{\text{in}}}}_{{{\text{Na}}^{ + } }}$$ J Na + in ) shortly after yolk sac absorption, but the mechanism of Na + accumulation differed between the species. Rainbow trout larvae greatly increased $$J^{{{\text{in}}}}_{{{\text{Na}}^{ + } }}$$ J Na + in to overcompensate for a large simultaneous increase in Na + -efflux rate ( $$J^{{{\text{out}}}}_{{{\text{Na}}^{ + } }}$$ J Na + out ), whereas pink salmon mounted a smaller increase in $$J^{{{\text{in}}}}_{{{\text{Na}}^{ + } }}$$ J Na + in while maintaining tight control over $$J^{{{\text{out}}}}_{{{\text{Na}}^{ + } }}$$ J Na + out , which is supported by a significantly lower paracellular permeability. Our results indicate that the transient accumulation of internal Na + is not a unique feature of the highly anadromous life history in pink salmon and may be a common ontogenetic pattern during larval development in salmonids; and perhaps it is associated with the development of the cardiovascular system during the larvae’s transition to a more active lifestyle.

中文翻译：

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粉红鲑鱼 (Oncorhynchus gorbuscha) 快速变体过程中 Na+ 平衡的个体发育

粉红鲑鱼在淡水中孵化，但它们高度溯河的生活史要求它们在砾石出现后立即以非常小的尺寸迁移到海洋中。在它们向下游迁移的过程中，这些幼虫经历了快速的熏蒸，完全重塑了它们的渗透调节生理机能。此时，据报道幼虫全身 Na + 含量很高，我们假设内部 Na + 的活跃积累发生在为进入海洋做准备。本研究使用比较方法表征了溯河粉红鲑鱼和淡水虹鳟鱼幼体中 Na + 调节的个体发育。我们的结果表明，两个物种的幼虫都积极积累 Na + ；然而，与粉红鲑鱼相比，虹鳟鱼幼虫的全身 Na + 含量更高。这种反应的时间过程在两个物种中相似，Na + 吸收率最高（ $$J^{{{\text{in}}}}_{{\text{Na}}^{ + } }$$ J Na + in ) 在卵黄囊吸收后不久，但 Na + 积累的机制因物种而异。虹鳟鱼幼虫大大增加了 $$J^{{{\text{in}}}}_{{{\text{Na}}^{ + } }}$$ J Na + in 以过度补偿同时大量增加Na + -外排率（ $$J^{{{\text{out}}}}}_{{{\text{Na}}^{ + } }}$$ J Na + out ），而粉红鲑鱼安装了一个$$J^{{{\text{in}}}}_{{{\text{Na}}^{ + } }}$$ J Na + in 的增幅较小，同时保持对 $$J^{ 的严格控制{{\text{out}}}}_{{{\text{Na}}^{ + } }}$$ J Na + out ，这是由显着较低的细胞旁通透性支持的。我们的结果表明，内部 Na + 的瞬时积累并不是粉红鲑鱼高度溯源生活史的独特特征，可能是鲑鱼幼体发育过程中常见的个体发育模式；也许这与幼虫向更积极的生活方式过渡期间心血管系统的发育有关。