Wang Feng-Yu, Fu Wen-Chun, Wang I-Li, Yan Hong Young, Wang Tzi-Yuan
Taiwan Ocean Research Institute, National Applied Research Laboratories, Kaohsiung, Taiwan.
Sensory Physiology Laboratory, Marine Research Station, Academia Sinica, I-Lan County, Taiwan.
PLoS One. 2014 Aug 7;9(8):e103953. doi: 10.1371/journal.pone.0103953. eCollection 2014.
Catadromous fishes migrate between ocean and freshwater during particular phases of their life cycle. The dramatic environmental changes shape their physiological features, e.g. visual sensitivity, olfactory ability, and salinity tolerance. Anguilla marmorata, a catadromous eel, migrates upstream on dark nights, following the lunar cycle. Such behavior may be correlated with ontogenetic changes in sensory systems. Therefore, this study was designed to identify changes in spectral sensitivity and opsin gene expression of A. marmorata during upstream migration. Microspectrophotometry analysis revealed that the tropical eel possesses a duplex retina with rod and cone photoreceptors. The λmax of rod cells are 493, 489, and 489 nm in glass, yellow, and wild eels, while those of cone cells are 508, and 517 nm in yellow, and wild eels, respectively. Unlike European and American eels, Asian eels exhibited a blue-shifted pattern of rod photoreceptors during upstream migration. Quantitative gene expression analyses of four cloned opsin genes (Rh1f, Rh1d, Rh2, and SWS2) revealed that Rh1f expression is dominant at all three stages, while Rh1d is expressed only in older yellow eel. Furthermore, sequence comparison and protein modeling studies implied that a blue shift in Rh1d opsin may be induced by two known (N83, S292) and four putative (S124, V189, V286, I290) tuning sites adjacent to the retinal binding sites. Finally, expression of blue-shifted Rh1d opsin resulted in a spectral shift in rod photoreceptors. Our observations indicate that the giant mottled eel is color-blind, and its blue-shifted scotopic vision may influence its upstream migration behavior and habitat choice.
降海洄游鱼类在其生命周期的特定阶段在海洋和淡水之间洄游。剧烈的环境变化塑造了它们的生理特征，例如视觉敏感度、嗅觉能力和耐盐性。花鳗鲡是一种降海洄游鳗鱼，会在农历月的黑夜里溯河而上。这种行为可能与感觉系统的个体发育变化有关。因此，本研究旨在确定花鳗鲡在溯河洄游过程中光谱敏感度和视蛋白基因表达的变化。显微分光光度法分析表明，这种热带鳗鱼拥有一个具有视杆和视锥光感受器的双重复合视网膜。在玻璃缸饲养的鳗鱼、黄色阶段鳗鱼和野生鳗鱼中，视杆细胞的最大吸收波长（λmax）分别为493、489和489纳米，而在黄色阶段鳗鱼和野生鳗鱼中，视锥细胞的最大吸收波长分别为508和517纳米。与欧洲和美洲鳗鱼不同，亚洲鳗鱼在溯河洄游过程中视杆光感受器呈现蓝移模式。对四个克隆的视蛋白基因（Rh1f、Rh1d、Rh2和SWS2）进行的定量基因表达分析表明，Rh1f在所有三个阶段的表达都占主导地位，而Rh1d仅在较老的黄色阶段鳗鱼中表达。此外，序列比较和蛋白质建模研究表明，Rh1d视蛋白的蓝移可能是由视网膜结合位点附近的两个已知调谐位点（N83、S292）和四个推测的调谐位点（S124、V189、V286、I290）诱导的。最后，蓝移的Rh1d视蛋白的表达导致视杆光感受器出现光谱偏移。我们的观察结果表明，花鳗鲡是色盲，其蓝移的暗视觉可能会影响其溯河洄游行为和栖息地选择。
