title: The giant mottled eel, Anguilla marmorata, uses blue-shifted rod photoreceptors during upstream migration.
abstract: 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.
authors.affiliation: Taiwan Ocean Research Institute, National Applied Research Laboratories, Kaohsiung, Taiwan.
authors.forename: Feng-Yu
authors.initials: FY
authors.lastname: Wang
authors.affiliation: Sensory Physiology Laboratory, Marine Research Station, Academia Sinica, I-Lan County, Taiwan.
authors.forename: Wen-Chun
authors.initials: WC
authors.lastname: Fu
authors.affiliation: Chemical Biology and Molecular Biophysics, Taiwan International Graduate Program, Institute of Biological Chemistry, Academia Sinica, Taipei, Taiwan; Institute of Biochemical Sciences, National Taiwan University, Taipei, Taiwan.
authors.forename: I-Li
authors.initials: IL
authors.lastname: Wang
authors.affiliation: Sensory Physiology Laboratory, Marine Research Station, Academia Sinica, I-Lan County, Taiwan; Hanse-Wissenschaftskolleg Institute for Advanced Study, Delmenhorst, Germany.
authors.forename: Hong Young
authors.initials: HY
authors.lastname: Yan
authors.affiliation: Biodiversity Research Center, Academia Sinica, Taipei, Taiwan.
authors.forename: Tzi-Yuan
authors.initials: TY
authors.lastname: Wang
mesh_terms: D000811:Anguilla / Q000502:physiology*; D025041:Animal Migration; D000818:Animals; D055253:Color Vision; D017753:Ecosystem; D018507:Gene Expression Regulation, Developmental; D055355:Opsins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010802:Phylogeny; D017948:Retinal Rod Photoreceptor Cells / Q000502:physiology*; D012243:Rhodopsin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013045:Species Specificity; D014785:Vision, Ocular / Q000502:physiology*
chemical_list: D055355:Opsins; D012243:Rhodopsin
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