Abstract
IntroductionEels 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.ResultsThe 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.ConclusionsThe 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.
Highlights
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
The present study is the first to report on characteristics of natural oogenesis in pike conger
Because naturally maturing samples can be captured, daggertooth pike conger may represent an excellent model for the study of reproduction in Anguilliformes
Summary
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. Seventy individuals were caught between June and October, which is supposed to be their spawning season, from inshore of the Seto Inland Sea. The unique catadromous nature of eels (Anguilla japonica, A. anguilla and A. rostrata), make them a representative species of the phylogenetically ancient group of Teleostei [1], and because of this feature they are commonly used experimental animals for zoological studies that involve migration, environmental adaptation, and reproduction. The unique catadromous nature of eels (Anguilla japonica, A. anguilla and A. rostrata), make them a representative species of the phylogenetically ancient group of Teleostei [1], and because of this feature they are commonly used experimental animals for zoological studies that involve migration, environmental adaptation, and reproduction This species grows in freshwater or in coastal areas of East Asia, but spawns offshore of the western North Pacific after extreme long-distance migrations [1,2,3,4]. We took up this study with an aim to Kobayashi et al Zoological Letters (2015) 1:25 obtain basic information on the reproduction of pike conger
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