Salmon lice (Lepeophtheirus salmonis) are marine parasitic copepods living on salmonids and are challenging for salmon aquaculture. One of several treatment methods is the application of freshwater to the fish which can lead to lice loss. However, lab experiments have shown that salmon lice, acclimated to seawater, are capable of surviving for several weeks in freshwater, when attached to a host. If not attached to a host, they die within a few hours in freshwater but can survive a longer time in brackish water. The molecular mechanisms involved in the adaptation to low salinity of the louse have not been identified yet. In this study we incubated salmon lice, being attached to a host, or detached, in seawater, brackish water and freshwater for 4 h and 1 d, sampled the animals and used RNA-Seq to identify genes involved in these mechanisms. Freshwater incubation led to a much stronger regulatory response than brackish water and a longer incubation time gave a stronger effect than a short incubation. Among the most interesting genes, upregulated in low salinity water are in addition to several transporters, several enzymes involved in amino acid metabolism and especially in the proline biosynthesis. A strong upregulation of these enzymes might lead to an accumulation of proline which is known to be used as an osmolyte in other species. While the RNA-Seq experiment was performed with female samples, qPCR showed that at least 10 genes regulated in females, were also regulated in males.

鲑鱼虱（Lepeophtheirus鲑) 是生活在鲑鱼上的海洋寄生桡足类动物，对鲑鱼水产养殖具有挑战性。几种处理方法之一是将淡水应用于鱼，这会导致虱子损失。然而，实验室实验表明，适应海水的鲑鱼虱附着在宿主身上时，能够在淡水中存活数周。如果不依附于宿主，它们在淡水中会在几小时内死亡，但在微咸水中可以存活更长的时间。尚未确定虱子适应低盐度的分子机制。在这项研究中，我们将附着于宿主或脱离宿主的鲑鱼虱在海水、微咸水和淡水中孵育 4 小时和 1 天，对动物进行采样并使用 RNA-Seq 来鉴定参与这些机制的基因。淡水孵化导致比微咸水更强烈的调节反应，更长的孵化时间比短孵化产生更强的影响。在最有趣的基因中，在低盐度水中上调的还有几种转运蛋白、几种参与氨基酸代谢尤其是脯氨酸生物合成的酶。这些酶的强烈上调可能导致脯氨酸的积累，众所周知，脯氨酸在其他物种中用作渗透剂。虽然 RNA-Seq 实验是用女性样本进行的，但 qPCR 显示至少有 10 个在女性中受到调控的基因在男性中也受到了调控。除了几种转运蛋白、几种参与氨基酸代谢尤其是脯氨酸生物合成的酶之外，在低盐度水中上调的还有。这些酶的强烈上调可能导致脯氨酸的积累，众所周知，脯氨酸在其他物种中用作渗透剂。虽然 RNA-Seq 实验是用女性样本进行的，但 qPCR 显示至少有 10 个在女性中受到调控的基因在男性中也受到了调控。除了几种转运蛋白、几种参与氨基酸代谢尤其是脯氨酸生物合成的酶之外，在低盐度水中上调的还有。这些酶的强烈上调可能导致脯氨酸的积累，众所周知，脯氨酸在其他物种中用作渗透剂。虽然 RNA-Seq 实验是用女性样本进行的，但 qPCR 显示至少有 10 个在女性中受到调控的基因在男性中也受到了调控。