Shiga Prefecture Fisheries Experiment Station

Shiga, Japan

Shiga Prefecture Fisheries Experiment Station

Shiga, Japan
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Sakai A.,Shiga Prefecture Fisheries Experiment Station | Endo M.,Shiga Prefecture Fisheries Experiment Station | Ide A.,Shiga Prefecture Fisheries Experiment Station
Aquaculture Science | Year: 2016

The daytime distribution of benthic juveniles of the genus Gymnogobius was described based on discrete depth sampling using a small trawl-net from 2 m to 40 m depth in Lake Biwa during July and August 1996. A total of 9,366 individuals were collected in this survey, most were G. isaza (93.0%) with a few G. urotaenia (3.9%) and morphologically unidentified specimens (3.1%). Juveniles of G. urotaenia were distributed in littoral areas shallower than 10 m depth, where the bottom is just at or above the thermocline. In contrast, juveniles of G. isaza were distributed in more off-shore areas, deeper than 10 m depth, and the density was highest depth of 10 m to 20 m i.e. just at or below the thermocline. The unidentified specimens were collected at depths 10 m to 20 m. In principal component analysis based on five morphometric characteristics (pre-anus length, caudal peduncle length, caudal peduncle depth, eye diameter and interorbital width), the unidentified specimens showed intermediate morphometric characteristics between G. isaza and G. urotaenia. This result suggests the possibility that they are hybrids between these two species. © 2016, Japanese Society for Aquaculture Research, Nishimura Toushadou Ltd. All rights reserved.


Fujioka Y.,Shiga Prefecture Fisheries Experiment Station | Fujioka Y.,Lake Biwa Museum | Okamoto H.,Shiga Prefecture Fisheries Experiment Station | Ishizaki D.,Shiga Prefecture Fisheries Experiment Station
Aquaculture Science | Year: 2016

The hatching time of eggs of honmoroko (Gnathopogon caerulescens), a small cyprinid fish endemic to Lake Biwa, was investigated under different rearing regimes of either constant temperature or fluctuating temperature representative of coastal water in Lake Biwa through the spawning season. Under constant temperature, eggs could hatch normally in the range of 10-29°C. Under fluctuating temperatures, spawning and hatching of eggs occurred in the range of 10-27°C and hatching rates of all batches of eggs were high. The hatching time was shorter at the fluctuating temperature than that of the same constant temperature. These results indicate that the lower temperature limit for hatching is 6-10°C, the upper temperature limit is 29-32°C, and the optimum temperature range is 10-29°C, coinciding nearly with the range of successful spawning and hatching under fluctuating temperature condition. Hatching time was more than 16 days in April and 7 days in June, and the water level of the lake should be maintained in order to protect the eggs laid at the lakeshore. © 2016, Japanese Society for Aquaculture Research, Nishimura Toushadou Ltd. All rights reserved.


Fujioka Y.,Shiga Prefecture Fisheries Experiment Station | Fujioka Y.,Lake Biwa Museum | Saegusa J.,Shiga Prefecture Fisheries Experiment Station
Ichthyological Research | Year: 2015

The age composition, and age- and size-dependent sex ratios of mass samples of “Honmoroko”, Gnathopogon caerulescens, were examined in Lake Biwa. The fish ranged from 0 to 2 years in age, but were mostly age 0 (97.9 %). The proportion of females was 48.6 % for age 0, 73.2 % for age 1, and 90.0 % for age 2 fish. Age 0 fish were significantly male biased, while ages 1 and 2 were significantly female biased, though the grand total showed a balanced sex ratio. The proportion of females was 48.0 % or less among age 0 fish in size classes of less than 9 cm in standard length (SL) and significantly different from a female:male ratio of 1:1 in such size classes, except for the 4–5.99 class. In size classes of 9 cm SL or greater, the proportion of females among age 0 fish was greater, more than 71.3 %, with significant differences from a balanced sex ratio for all such classes. These results suggest that G. caerulescens can be regarded as essentially an annual fish and that its spawning habits ought to result in a higher mortality for males than females, thus leading to female-biased sex ratios at ages 1 and 2. © 2014, The Ichthyological Society of Japan.


Fujiwara K.-I.,Shiga Prefecture Fisheries Experiment Station | Fujiwara K.-I.,Tokyo University of Marine Science and Technology | Usuki T.,Shiga Prefecture Fisheries Experiment Station | Nemoto M.,Shiga Prefecture Fisheries Experiment Station | Kitada S.,Tokyo University of Marine Science and Technology
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2011

The early life ecology of nigorobuna Carassius auratus grandoculis was investigated in order to determine the requirements for developing breeding grounds and effective release sites for its stock enhancement in Lake Biwa. Larval nigorobuna within the well-developed reed zone swarmed actively near the shoreline immediately after release and began to leave the reed zone when they grew to the juvenile stage of approximately 16 mm in standard length. Zooplankton used as food for the larvae were abundant near the shoreline in the reed zone, but there was remarkably little dissolved oxygen. It was confirmed that the larvae have a high hypoxia tolerance and due to their low body specific gravity could easily rise to the water surface where oxygen readily dissolved. The results indicate adaptation of the larvae to the hypoxic environmental condition. It was thought that hypoxic water areas function as feeding sites and as refuges for the larvae.


Fujiwara K.-I.,Shiga Prefecture Fisheries Experiment Station
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2012

The influence of winter reaping of withered stems of the reed Phragmites australis on their budding and growth was examined in Lake Biwa. When the cut ends of withered stems were flooded in spring, growth of new shoots was inhibited probably because of limited oxygen supply to the rhizomes. As an adaptation, the reeds rapidly extended shoots to the water surface to obtain oxygen. However, it was thought that this adaptation would not function easily in natural lake areas because these shoots were easily damaged by wind and waves. On the other hand, it was confirmed that withered stems have a function to protect new shoots from wind and waves. Furthermore, the importance of the humus originating from the litter of reeds was confirmed for the budding and growth of the reeds. Thus, it was concluded that the withered stems should not be reaped in areas where submergence is expected at the time of budding.


Sakai A.,Shiga Prefecture Fisheries Experiment Station | Usuki T.,Shiga Prefecture Fisheries Experiment Station | Kataoka Y.,Shiga Prefecture Fisheries Experiment Station
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2015

The characteristics of overwinter mortality of juvenile ayu Plecoglossus altivelis altivelis were studied in Lake Biwa in 1999 and 2002-2010. The positive correlation between CPUE of ayu in set nets in February and April was significant except for 2006, when heavy mortality occurred during February to April. In 2006, the water temperature was the lowest in the 10 years, and plankton biomass was at a relatively low level from January to April. The condition of ayu in mid-February 2006 was relatively poor. The heavy mortality during the 2006 winter may have resulted from low-temperature stress and deterioration of nutritional status.


Fujioka Y.,Lake Biwa Museum | Ueno S.,Shiga Prefecture Fisheries Experiment Station
Fisheries Science | Year: 2014

The honmoroko has been inferred to have an XX/XY sex determination system, but the parental genome can also affect the sex ratio of the offspring. The extent of parental effects on sex determination was examined by checking the sex ratios of F1 and F2 gynogenetic diploids and control diploids. Eleven gynogenetic broods from different females consisted of all or nearly all females, but eight broods showed a variable proportion of males (<50 %). One second-generation brood of gynogenetic diploids consisted wholly of females, but others produced some males. In crosses with a control diploid female, four males from a high-percentage male brood of gynogenetic diploids produced offspring with a balanced sex ratio. Sib-mating between a gynogenetic female and three gynogenetic males from the brood produced predominantly male progeny. These results suggest that there are at least four possible genotypes: genotypic female (XX), phenotypic female carrying a silent Y chromosome, genotypic male (XY), and genotypic supermale (YY). These inferences suggest that this fish has an XY system but a relatively high proportion of females possess a mutated, silent Y chromosome which does not lead to testis formation. © 2014, Japanese Society of Fisheries Science.


Sakai A.,Shiga Prefecture Fisheries Experiment Station
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2010

This study was conducted to examine the relationships among the effects of population density, mean standard length, plankton biomass, water temperature and precipitation on the first ascending day of ayu Plecoglossus altivelis altivelis and the number individuals ascending the Ado River, Lake Biwa. Effects of four factors on fluctuations of the first ascending day (Y1) in the river were recognized by multiple regression analysis. The factors were as follows: number of ayu caught by a set net in March (X1), mean standard length of ayu in mid-March (X2), plankton biomass in mid-March (X3), and water temperature in Lake Biwa in mid-March (X4). In addition, effects of four factors on fluctuations in the number of ascending individuals of ayu (Y2) in the river from April to June were recognized. The factors were as follows: X1, X2, X3, and amount of precipitation from April to June (X5). The following equations were obtained by multiple regression analysis of the factors except X5 for the forecast. Y1 = - 0.316X1-3.14X2-1.29X3-9.25X4+290(p<0.001) Y2 = 9.09X1+17.5X2+55.3X3-988 (p<0.001) These equations can be used to forecast the first ascending day and the number of ascending ayu individuals in the river.


Fujiwara K.-I.,Shiga Prefecture Fisheries Experiment Station
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2010

The morphological development, organogenesis and somatic growth of hatchery-reared nigorobuna Carassius auratus grandoculis from newly-hatched larvae to early stage of juveniles were investigated in order to obtain basic data for determining the effective size at release for the stock enhancement program in Lake Biwa. As a result, generally the completion of the fin rays, scales and skeleton, and rapid development of the skeletal muscles and organs for digestion, respiration, circulation, hematogenesis, excretion and sensory perception were observed at the juvenile stage of approximately 16 mm in standard length (SL), leading to an improved ability to survive under natural environmental conditions. It was concluded that this developmental stage (ca. 16 mm SL) is a criterion for determining the effective size at release.


PubMed | Lake Biwa Museum and Shiga Prefecture Fisheries Experiment Station
Type: Journal Article | Journal: Journal of fish biology | Year: 2015

The influence of hatching date on the sex ratio of wild Gnathopogon caerulescens was examined. Cohorts reared from eggs collected in the early and middle parts of the spawning season showed almost balanced sex ratios, with female bias in some cohorts. Cohorts born later in the season mostly displayed male bias, and the mean proportion of males later in the season was significantly higher than in early- and mid-season cohorts. These results indicate that the sex ratio of G. caerulescens changes with the time of breeding, increasing along with the ambient water temperature of the lake.

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