During their ontogenetic development, many species of fishes undergo drastic changes which may be defined as true metamorphosis when they are induced by thyroid hormones. Sicyopterus lagocephalus is an amphidromous goby that has to change biome twice during its life cycle. The first biome shift occurs few hours after hatching in the river. The aim of the present study is to determine what external/environmental and internal/endocrine factors induce the transformation of freshwater prolarvae into marine larvae. First, we experimentally determined that the minimum salinity threshold inducing the transformation of all the prolarvae into marine larvae is 1.5, whereas a salinity of 0.2 induces the transformation of a few prolarvae. Similarly, an 18-h immersion in seawater before the return to freshwater is enough to induce the transformation of all the prolarvae into marine larvae, even though an immersion for 3 h can induce the transformation of a few prolarvae. Furthermore, we demonstrated that a simulated increase in the osmotic pressure of freshwater does not trigger the transformation of the prolarvae into marine larvae. Our study also reveals that among the various constituent salts of seawater, it is primarily NaCl and K⁺ that induce the transformation of the prolarvae, leading to the assumption that the membrane protein Na⁺/K⁺-ATPase is activated simultaneously with the prolarval transformation. Finally, we showed that thyroid hormones and cortisol are not involved in the prolarval transformation, leading to the conclusion that this first transformation in the life cycle of S. lagocephalus cannot be considered as a true metamorphosis.

中文翻译：

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寻找环境和内分泌因素，以诱导水头Si（Sicyopterus lagocephalus）（Pallas 1770）（Teleostei：戈壁科：Sicydiinae）的淡水幼体转化成海洋幼体。

在其个体发育过程中，许多鱼类经历了剧烈的变化，当它们被甲状腺激素诱导时，可被定义为真正的变态。头尾轮虫是一种两栖性虾虎鱼，在其生命周期中必须两次更换生物群落。第一次生物群落转移发生在河中孵化后的几个小时。本研究的目的是确定哪些外部/环境因素和内部/内分泌因素诱导了淡水幼体向海洋幼体的转化。首先，我们通过实验确定诱导所有幼体向海洋幼体转化的最低盐度阈值为1.5，而盐度为0.2则诱导一些幼体转化。同样，在返回淡水之前在海水中浸泡18小时足以诱导所有幼体转化为海洋幼体，即使浸泡3小时可以诱导一些幼体转化。此外，我们证明淡水的渗透压的模拟增加不会触发幼体向海洋幼体的转化。我们的研究还表明，在海水的各种组成盐中，主要是NaCl和K⁺引起原肠转化，导致推测膜蛋白Na ⁺ / K ⁺ -ATPase与原肠转化同时被激活。最后，我们证明甲状腺激素和皮质醇不参与原发性转变，从而得出结论，这是S生命周期中的第一个转变。头颅脑畸形不能被视为真正的变态。