Papers Published in Japanese Journal of Ichthyology

Vol. 61, No. 1April 25, 2014

CONTENTS
Full Papers
Spawning ecology of Honmoroko, Gnathopogon caerulescens, in inlets of theNishinoko lagoon, Lake Biwa
Takeshi Kikko, Haruo Okamoto, Muneji Ujiie, Daisuke Ishizaki, Takahiro Usuki,
Morihito Nemoto, Jin Saegusa, Yoshiaki Kai and Yasuhiro Fujioka
Viable periods of fertilizability of eggs and sperm of Japanese medaka, Oryzias
latipes
Yukari Koike and Yasunori Koya
Reproductive population dynamics of the Far Eastern Catfish, Silurus asotus
estimated from mark and recapture and Bayesian modelingToshinori Funao, Koh-ichi Takakura, Takayoshi Nishida and Hiroichi Sawada

Short Reports
First Japanese record of the eyelight fish Photoblepharon palpebratum fromOkinawa Island
Keita Koeda, Takuma Fujii and Tetsuo Yoshino

Full Papers
Japanese Journal of Ichthyology
Vol. 61, No. 1, pp. 1–8

Spawning ecology of Honmoroko, Gnathopogon caerulescens, in inlets of theNishinoko lagoon, Lake Biwa
Takeshi Kikko, Haruo Okamoto, Muneji Ujiie, Daisuke Ishizaki, Takahiro Usuki,

Morihito Nemoto, Jin Saegusa,Yoshiaki Kai and Yasuhiro Fujioka
Abstract To clarify the reproductive ecology of the endangered cyprinid Honmoroko,Gnathopogon caerulescens, endemic to Lake Biwa, the occurrence of eggs in inlets, sex
ratio and monthly changes in gonad somatic indices (GSI) were investigated in theNishinoko lagoon, adjacent to Lake Biwa, from March to May, 2012. Eggs ofHonmoroko were found on gravel and vegetation in two inlets, suggesting that not only
the reed zone of Lake Biwa and its lagoons but also inlets of the lagoons are important
spawning habitats of that species. The sex ratios of individuals collected in the two inlets
were more male-biased (11.2–32.1:1) than that in the reed zone of the lagoon (1.5–2.7:1).
The GSI of males gradually decreased as the breeding season progressed, those offemales not showing any significant statistical changes, except for individuals collectedaround the reed zone and inlet in April. It was concluded that males remain in inlets andthe reed zone during spawning, whereas females migrate to the inlets only for spawning,
subsequently returning to the reed zone until the next spawning session.
(Corresponding author: Takeshi Kikko, Shiga Prefectural Fisheries Experimental
Station,2138-3,Hassaka,Hikone,Shiga,522-0057,

Japan;

e-mail:kikkou-takeshi@pref.shiga.lg.jp)

Japanese Journal of Ichthyology
Vol. 61, No. 1, pp. 9–14

Viable periods of fertilizability of eggs and sperm of Japanese medaka, Oryzias
latipes
Yukari Koike and Yasunori Koya
Abstract

In order to clarify the period during which eggs and sperm of Oryzias latipes

remained viable following release into fresh water, the fertilization rate of eggs over time
following immersion in fresh water, was investigated, in addition to sperm motility.
Fertilizability of the eggs persisted for more than 6 minutes after immersion, but was lost

after more than 10 minutes in some cases. Sperm retained motility for about 2–3 minutes
in fresh water, being affected by osmolality; motility was high in 100–300 mOsm/kg, butabsent in 700 mOsm/kg. These results suggested that O. latipes eggs can be fertilized forup to 6 minutes following spawning in fresh water, whereas sperm remain viable for only
2–3 minutes following released.
(Corresponding author: Yasunori Koya: Faculty of Education, Gifu University,Yanagido, Gifu 501–1193, Japan; e-mail: koya@gifu-u.ac.jp)

Japanese Journal of Ichthyology
Vol. 61, No. 1, pp. 15–26

Reproductive population dynamics of the Far Eastern Catfish, Silurus asotus
estimated from mark and recapture and Bayesian modelingToshinori Funao, Koh-ichi Takakura, Takayoshi Nishida and Hiroichi Sawada
Abstract

Owing to growing concerns for the conservation of the Far Eastern Catfish,

Silurus asotus, due to declining numbers of the species resulting from a recent reductionin spawning sites, the dynamics of a reproductive population were investigated in
Imagawa creek on the east shore of Lake Biwa Hikone City, Shiga Prefecture, central
Japan. The frequency of ascent into the creek for reproduction was determined from amark-release-recapture method and construction of a Bayesian model. Field observations
and the model analysis revealed the sex ratio of the population to be clearlyfemale-biased. Although the more frequent upstream migration of males compared withfemales was not statistically significant, it was suggestive of more frequent reproductiveactivity in males. These findings differed from those of a previous study on the west
shore of Lake Biwa, in which large, site-related variations in the reproductive ecology S.
asotus had been suggested. The frequent migration of males observed in the present study
may be ascribed to the presence of spawning females even in the late reproductive
season.

(Corresponding author: Toshinori Funao: Laboratory of Environmental Zoology,
Graduate School of Environmental Science, The University of Shiga Prefecture, 2500
Hassaka-cho, Hikone-city, Shiga 522–8533, Japan; e-mail: t.funao702@gmail.com)

Short Reports
Japanese Journal of Ichthyology
Vol. 61, No. 1, pp. 27–31

First Japanese record of the eyelight fish Photoblepharon palpebratum from Okinawa
IslandKeita Koeda, Takuma Fujii and Tetsuo Yoshino
Abstract

A single specimen of Photoblepharon palpebratum (Boddaert, 1781),

formerly limited to the tropical western Pacific, was collected from Okinawa Island,
Japan at a depth of 1 m. The specimen was characterized by the following combination ofcharacters: single dorsal fin with 3 spines; a black shutter lifting to cover the subocularorgan; a large white spot on the dorsal corner of the opercle; pelvic-fin rays I, 6. The tiny
first dorsal-fin spine was identified from a radiograph. The specimen represents the firstrecord of P. palpebratum from Japan and is the northernmost record of the species. The
specimen produced a total of 273 eggs, but those were probably postmaturity.
(Corresponding author: Keita Koeda: University of the Ryukyu, 1 Senbaru, Nishihara,Okinawa, 903–0213, Japan; e-mail: hatampo@gmail.com)