title: Prolongation of somitogenesis in two anguilliform species, the Japanese eel Anguilla japonica and pike eel Muraenesox cinereus, with refined descriptions of their early development.
abstract: The embryonic development of the Japanese eel Anguilla japonica and pike eel Muraenesox cinereus was morphologically investigated with laboratory-reared specimens to clarify the characteristics of somitogenesis. In A. japonica, somites were first observed at 18 h post fertilization (hpf) when epiboly reached 90%. Somitogenesis progressed at a rate of 1·6 h-1at mean ± s.d. 22·6 ± 0·7° C and completed at 107 hpf (3 days post hatching; dph) when total number of somites (ST) reached 114, which corresponds to the species' number of vertebrae (112-119). In M. cinereus, somites were first observed at 14 hpf when epiboly completed. Somitogenesis progressed at a rate of 1·9 h-1at mean ± s.d. 24·4 ± 0·2° C and completed at 90 hpf (2 dph) with 149 ± 4 ST, which corresponds to the species' number of vertebrae (142-158). Both species hatched before somitogenesis was completed, at 37 hpf with 47 ST and 42 hpf with 82 ± 4 ST, respectively. The formation of other organs such as the heart, mouth and pectoral fin bud occurred during somitogenesis. Comparison with the development of zebrafish Danio rerio indicates a prolongation of somitogenesis in A. japonica and M. cinereus. Their somitogenesis rates, however, correspond well with that of D. rerio estimated at the same temperature and their developmental stages at hatching are almost equivalent to other fishes having similar yolk sizes. Therefore, the prolongation of somitogenesis in A. japonica and M. cinereus may be accounted for solely by the increased numbers of somites to be formed, not by a slow somitogenesis rate or an acceleration in organogenesis.
authors.affiliation: Atmosphere and Ocean Research Institute, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8564, Japan.|Graduate School of Agricultural and Life Sciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-8657, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Kawakami
authors.affiliation: IRAGO Institute, 377 Ehima-Shinden, Tahara, Aichi, 441-3605, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Yamada
authors.affiliation: IRAGO Institute, 377 Ehima-Shinden, Tahara, Aichi, 441-3605, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Tanaka
authors.affiliation: Atmosphere and Ocean Research Institute, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8564, Japan.|College of Bioresource Sciences, Nihon University, 1866 Kameino, Fujisawa, Kanagawa, 252-0880, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Tsukamoto
mesh_terms: D000811:Anguilla / Q000196:embryology* / Q000235:genetics*; D000818:Animals; D047108:Embryonic Development / Q000502:physiology*; D038081:Organogenesis / Q000502:physiology*; D013045:Species Specificity
keywords: anguilliformes; egg; embryo; heterochrony; larva; morphology