title: Basic reproductive biology of daggertooth pike conger, Muraenesox cinereus: A possible model for oogenesis in Anguilliformes.
abstract: BACKGROUND
  Eels are animals commonly used in zoological research, as these species have a unique catadromous life history and belong to a phylogenetically ancient group of Teleostei. However, eel reproduction is difficult to investigate, since mature samples are not easily obtainable in the wild. In this study, we tested daggertooth pike conger (Muraenesox cinereus), an Anguilliformes species, as a potential model for the investigation of the reproductive biology of eels. Seventy individuals were caught between June and October, which is supposed to be their spawning season, from inshore of the Seto Inland Sea.
  
  
  RESULTS
  The lengths and ages of samples ranged from 510 to 1239 mm and three to nine years, respectively, and the sex ratio was skewed towards females (96 % of the total sample). The gonado-somatic index of the females peaked in July. Histological observation revealed that these ovaries were similar to those of other eel species and contained matured oocytes (migratory-nucleus stage), suggesting that pike conger spawn inshore in July. The plasma concentrations of sex steroid hormones (estradiol-17β and 11-keto-testosterone) in females gradually increased during maturation and decreased after spawning, indicating the involvement of these hormones in oogenesis of pike conger.
  
  
  CONCLUSIONS
  The present study is the first to report on characteristics of natural oogenesis in pike conger. Because naturally maturing samples can easily be captured, daggertooth pike conger may represent an excellent model for the study of reproduction in Anguilliformes.
authors.affiliation: Ushimado Marine Institute (UMI), Faculty of Science, Okayama University, Ushimado, Setouchi, 701-4303 Japan.
authors.forename: Yasuhisa
authors.initials: Y
authors.lastname: Kobayashi
authors.affiliation: Okayama Prefectural Technology Center for Agriculture, Forestry and Fisheries, Research Institute for Fisheries Science, Ushimado, Setouchi, 701-4303 Japan.
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Mototani
authors.affiliation: Okayama Prefectural Technology Center for Agriculture, Forestry and Fisheries, Research Institute for Fisheries Science, Ushimado, Setouchi, 701-4303 Japan.
authors.forename: Fumiyasu
authors.initials: F
authors.lastname: Murayama
authors.affiliation: Ushimado Marine Institute (UMI), Faculty of Science, Okayama University, Ushimado, Setouchi, 701-4303 Japan.
authors.forename: Tatuya
authors.initials: T
authors.lastname: Sakamoto
keywords: Conger; Eel; Gonad; Ovary; Reproduction; Testis