Department of Human Nutrition, Food, and Animal Sciences, University of Hawai'i at Mānoa, Honolulu, HI, 96822, USA.
Hawai'i Institute of Marine Biology, University of Hawai'i, Kaneohe, HI, 96744, USA.
J Comp Physiol B. 2019 Oct;189(5):581-594. doi: 10.1007/s00360-019-01233-9. Epub 2019 Sep 4.
Euryhaline Mozambique tilapia (Oreochromis mossambicus) are native to estuaries where they encounter tidal fluctuations in environmental salinity. These fluctuations can be dramatic, subjecting individuals to salinities characteristic of fresh water (FW < 0.5‰) and seawater (SW 35‰) within a single tidal cycle. In the current study, we reared tilapia under a tidal regimen that simulated the dynamic conditions of their native habitat. Tilapia were sampled every 3 h over a 24 h period to temporally resolve how prolactin (PRL) signaling is modulated in parallel with genes encoding branchial effectors of osmoregulation. The following parameters were measured: plasma osmolality, plasma PRL and PRL concentrations, pituitary prl and prl gene expression, and branchial prl receptor (prlr1 and prlr2), Na/Cl-cotransporter (ncc2), Na/K/2Cl-cotransporter (nkcc1a), Na/K-ATPase (nkaα1a and nkaα1b), cystic fibrosis transmembrane regulator (cftr), and aquaporin 3 (aqp3) gene expression. Throughout the 24 h sampling period, plasma osmolality reflected whether tilapia were sampled during the FW or SW phases of the tidal cycle, whereas pituitary prl gene expression and plasma PRL levels remained stable. Branchial patterns of ncc2, nkcc1a, nkaα1a, nkaα1b, cftr, and aqp3 gene expression indicated that fish exposed to tidally changing salinities regulate the expression of these gene transcripts in a similar fashion as fish held under static SW conditions. By contrast, branchial prlr1 and prlr2 levels were highly labile throughout the tidal cycle. We conclude that local (branchial) regulation of endocrine signaling underlies the capacity of euryhaline fishes, such as Mozambique tilapia, to thrive under dynamic salinity conditions.
广盐性莫桑比克罗非鱼（Oreochromis mossambicus）原产于河口，在那里它们会遇到环境盐度的潮汐波动。这些波动可能非常剧烈，导致个体在一个潮汐周期内经历从淡水（FW<0.5‰）到海水（SW 35‰）的盐度变化。在当前的研究中，我们在模拟其天然栖息地动态条件的潮汐方案下饲养罗非鱼。在 24 小时的时间内，每 3 小时采集一次罗非鱼样本，以时间分辨的方式确定催乳素（PRL）信号是如何与鳃渗透压调节效应器的基因表达同时被调节的。测量了以下参数：血浆渗透压、血浆 PRL 和 PRL 浓度、垂体 prl 和 prl 基因表达以及鳃 PRL 受体（prlr1 和 prlr2）、Na/Cl-协同转运蛋白（ncc2）、Na/K/2Cl-协同转运蛋白（nkcc1a）、Na/K-ATP 酶（nkaα1a 和 nkaα1b）、囊性纤维化跨膜转导调节因子（cftr）和水通道蛋白 3（aqp3）基因表达。在 24 小时的采样期间，血浆渗透压反映了罗非鱼是在潮汐周期的 FW 还是 SW 阶段被采样的，而垂体 prl 基因表达和血浆 PRL 水平保持稳定。鳃 ncc2、nkcc1a、nkaα1a、nkaα1b、cftr 和 aqp3 基因表达的模式表明，暴露于潮汐变化盐度下的鱼类以与在静态 SW 条件下饲养的鱼类相似的方式调节这些基因转录本的表达。相比之下，鳃 prlr1 和 prlr2 水平在整个潮汐周期内都高度不稳定。我们得出结论，内分泌信号的局部（鳃）调节是像莫桑比克罗非鱼这样的广盐性鱼类在动态盐度条件下茁壮成长的基础。
