Kagawa Prefectural Fisheries Experimental Station

Takamatsu-shi, Japan

Kagawa Prefectural Fisheries Experimental Station

Takamatsu-shi, Japan
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Yamamoto M.,Kagawa Prefectural Fisheries Experimental Station | Shoji J.,Hiroshima University
Aquaculture Science | Year: 2016

To examine seasonal changes in composition of dominant species in demersal fish community on a sandy beach in the Seto Inland Sea, we conducted a beam trawl survey between May 2002 and September 2005. A total of 14,013 individuals, belonging to more than 39 species, were collected at 1.0-5.7 m depths (measured at each tow). The tidal variation was approximately 3 m at this beach, the water temperature ranged from 9.0 (February) to 30.3°C (August), and the salinity from 28.7 (July) to 33.7 (March). The mean number of fish species per tow ranged from 1.25 (January) to 9.50 (June) and fish abundance (number of individuals /100 m2) from 0.6 (January) to 103.5 (October). Both species number and the abundance increased from spring to summer and decreased from autumn to winter with a significant positive correlation with water temperature each month. The numerically dominant species were Favonigobius gymnauchen (62.6%), Tarphops oligolepis (11.4%), Sillago japonica (6.7%), unidentified Repomucenus (6.4%), Heteromycteris japonica (3.3%) and Paralichthys olivaceus (3.2%). © 2016, Japanese Society for Aquaculture Research, Nishimura Toushadou Ltd. All rights reserved.

Tada K.,Kagawa University | Fujiwara M.,Kagawa Prefectural Fisheries Experimental Station | Honjo T.,Kagawa University
Bunseki Kagaku | Year: 2010

The water quality of the Seto Inland Sea has recently improved compared with that in the 1970s and early 1980s, but the fisheries yield of species such as sardine and short-neck clam has decreased. Since 2002, the Nori (Porphyra) culture has been particularly heavily damaged due to a lack of nutrients. In this paper, we review our previous water quality results of the Seto Inland Sea, which focused on the Nori culture directly influenced by the nutrient concentrations. Moreover, we discuss the potential mechanism for low levels of dissolved inorganic nitrogen (DIN) concentrations and poor Nori production. Our results suggest that the reasons for the recent decreases in nutrient concentrations are (1) decrease of nutrient loading from riverine sources, (2) an increase of nutrient uptake by phytoplankton growth due to an increase of euphotic depth, (3) the diffusion of nutrients in the bottom marine layer due to a decrease in stratification, and (4) a decrease of the upward nutrient flux across the overlying water-sediment interface. © 2010 The Japan Society for Analytical Chemistry.

Ogawa K.,Meguro Parasitological Museum | Iwaki T.,Meguro Parasitological Museum | Itoh N.,Tohoku University | Nagano T.,Kagawa Prefectural Fisheries Experimental Station
Fish Pathology | Year: 2012

A long, tubular "parasite" was found in the muscle of greater amberjack Seriola dumerili cultured in Kagoshima and Miyazaki prefectures. Infection with this parasite was very rare, only occurring in two amberjacks from Kagoshima and one from Miyazaki. Molecular analysis indicates the parasite is a cestode of the order Trypanorhyncha, most closely related to the subfamily Grillotiinae, family Lacistorhynchidae. The tubular structure was a blastocyst. There was no evidence of the scolex in the blastocysts, which may not have been sampled intact, making it impossible to identify the parasite. This is the first report of Trypanorhyncha infection in greater amberjack in Japan. © 2012 The Japanese Society of Fish Pathology.

Shan B.,Ocean University of China | Song N.,Ocean University of China | Han Z.,Zhejiang Ocean University | Wang J.,Chinese Academy of Fishery Sciences | And 2 more authors.
Biochemical Systematics and Ecology | Year: 2016

Genus Lateolabrax consists of three species, Japanese sea bass Lateolabrax japonicus, spotted sea bass Lateolabrax maculatus and blackfin sea bass Lateolabrax latus. The complete mitochondrial DNA (mtDNA) of the three sea basses were amplified and sequenced to characterize and discuss their phylogenetic relationships. The length of mitogenomes was 16,593 bp, 16,479 bp and 16,600 bp, respectively, and all of them consisted of 13 protein-coding genes, 2 ribosomal RNA (rRNA), 22 transfer RNA (tRNA) and a control region, which are typical for mtDNA of vertebrate. Most genes were encoded on the H-strand, except for the ND6 and eight tRNA genes encoding on the L-strand. A significant variation among the three species was detected in length of the control region. Phylogenetic relationship among the three species was constructed based on the datasets, including the 12 protein-coding genes (except ND6 gene), 22 tRNA and 2 rRNA sequences. The results supported the sister taxon between L. japonicus and L. maculatus. The genetic resources reported here are useful for further studies in taxonomy and phylogeny of the three sea basses and related species. © 2016 Elsevier Ltd.

Tomiyama T.,Hiroshima University | Katayama S.,Tohoku University | Yamamoto M.,Kagawa Prefectural Fisheries Experimental Station | Shoji J.,Hiroshima University
Journal of Sea Research | Year: 2016

Pleuronectid flatfish are considered visual day feeders, but their ability to feed at night has not been examined in the field. Juvenile (age-0) stone flounder Platichthys bicoloratus were collected, and their stomach contents were investigated in situ every 4 h over a 24-h period in an estuarine habitat to elucidate diel feeding periodicity. The weight of juvenile stomach contents was usually the highest around dusk and the main prey was bivalve siphons. To reveal whether juveniles feed only at particular times during the day or throughout a 24-h period, we conducted 24-h cage experiments in which 10 juveniles with empty stomachs were held in a cage for approximately 4 h (six trials). This experiment was carried out three times during different moon phases. Juveniles primarily ingested prey during the day, but 30% of fish that were caged at night also ingested prey. The number of successful captures by the caged fish was much greater during the day than that at night. These results indicate that stone flounder generally feed during the day and they may only feed at night under unusual situations, although they have the ability to capture prey at night. The mean daily ration estimated by diel changes in stomach content weight varied from 3.4% (95% confidence interval, 1.8-4.8%) to 13.2% (11.0-15.6%) of body weight between survey dates, indicating that daily food consumption by fish estimated from a single survey may be strongly biased. © 2015 Elsevier B.V.

Koike K.,Hiroshima University | Akai N.,Kagawa Prefectural Fisheries Experimental Station | Liao L.M.,Hiroshima University | Ikeda S.,Hiroshima University | Yoshimatsu S.,Akashiwo Research Institute of Kagawa Prefecture
Parasitology International | Year: 2013

A green spotted Japanese sillago (Sillago japonica) was caught by a fisherman and brought to the laboratory for pathological inspection. The green spots were abundant on the lateral line and more extensively so within the mouth cavity. In both sites, green spots were embedded within the fish flesh and formed 2-3. mm dome-shaped colonies. SEM revealed these colonies to harbor numerous unknown cells with small, surface warts (ornamentations). Molecular analysis showed the cells were Desmodesmus (D. komarekii), a common freshwater coccoid green alga found in ponds and rivers worldwide. It is uncertain how the host fish came to be infected with the alga which was not merely attached externally but embedded within the flesh and inside the mouth cavity. This is the first case of parasitic form of coccoid green algae in marine fish and provides new insights into the variable nature of green algae. © 2013 Elsevier Ireland Ltd.

Katayama S.,Japan National Research Institute of Fisheries Science | Yamamoto M.,Kagawa Prefectural Fisheries Experimental Station | Gorie S.,Hyogo Prefectural Institute of Technology
Journal of Sea Research | Year: 2010

We developed an ageing methodology and examined age composition of three flatfish stocks inhabiting the Seto Inland Sea, Japan. Ages were difficult to determine for three-lined tongue sole (Cynoglossus abbreviates) and ridged-eye flounder (Pleuronichthys cornutus) because the first year annulus ring was often indistinct; therefore, we used directional change in otolith growth to distinguish it. Sectioning and etching methods were powerful tools for identifying annual checks for red tongue sole (Cynoglossus joyneri). Using these ageing methods, we determined age-length relationships and growth curves. The age composition of the populations studied and of the landings showed that a large proportion of the latter consisted of individuals under the mean age of sexual maturity, thereby reducing the percent spawning potential ratio (%SPR) to ≈ 20% for all species. These findings suggest that fishing pressure on immature fish is leading to overfishing of these flatfish stocks. © 2010 Elsevier B.V.

Nakajima K.,Tokyo University of Marine Science and Technology | Kitada S.,Tokyo University of Marine Science and Technology | Yamazaki H.,Japan National Research Institute of Fisheries And Environment of Inland Sea | Takemori H.,Kagawa Prefectural Fisheries Experimental Station | And 3 more authors.
Aquaculture Environment Interactions | Year: 2013

If the release of hatchery-reared juveniles exceeds the carrying capacity of the environment, the growth rate of wild fish may decrease or hatchery fish might displace wild fish because of competition for prey and space, or cannibalism. However, limited evidence is available to confirm these ecological effects. Therefore, we used census-marking experiments to investigate the ecological interactions between hatchery and wild fish in the large piscivorous species Japanese Spanish mackerel (JSM) Scomberomorus niphonius in the Seto Inland Sea. We analysed the relationship between the mean body weight and population size of Age 0 JSM, and the relationship between the biomass of juvenile Japanese anchovy Engraulis japonicus, which is the principal prey fish of JSM, and that of Age 0 JSM. We also estimated the spawner-recruit relationship. We measured the body sizes of 5008 JSM juveniles during July and December between 1999 and 2005 in the eastern Seto Inland Sea, and 551 hatchery fish were identified in the sample based on examinations of marked otoliths. There was a negative correlation between the mean body weight and population size of Age 0 fish, which clearly demonstrated the density-dependent growth of Age 0 JSM. The ~35% variation in the biomass of Age 0 JSM was explained by the biomass of prey fish. Hatchery fish tended to be larger than wild fish, and they had better growth performance. Our analysis showed that hatchery fish reduced the growth rate of wild fish and displaced the wild fish in terms of biomass when hatchery fish stocking exceeded the carrying capacity of the environment. © The authors 2013.

Akai N.,Kagawa Prefectural Fisheries Experimental Station | Utsumi N.,Kagawa Prefectural Fisheries Experimental Station
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2012

The effects of high water temperature during the estivation period on the mortality and reproduction of Japanese sand lance Ammodytes personatus collected in the Seto Inland Sea were examined through a rearing experiment. Specimens were reared at three water temperatures (24, 26 and 28°C) during the months from August to September in 2010 after a two-month acclimation. Cumulative mortality in these conditions during the first three months was 3.0,13.7 and 29.7%, respectively, showing a tendency to higher mortalities with higher temperature during the estivation period. The condition factor of the specimens in the 28°C group significantly decreased one month later and this tendency continued until they were returned to the natural water temperature. In late December, specimens in each experiment generally matured. However, a decrease of both fecundity and male testicular weight was observed in specimens from the 28°C group. In the Bisan Strait in 1994, a year with abnormally high water temperature, the water temperature remained above 28°C for over one month. Therefore, we suggest that a sustained period of high water temperature during estivation affects not only the survival rate and condition factor of wild sand lance but also their reproduction.

Yamamoto M.,Kagawa Prefectural Fisheries Experimental Station | Tominaga O.,Fukui Prefectural University
Fisheries Science | Year: 2014

The aim of this study was to characterize a nursery ground (Ohama Beach, Hiuchi-nada) for the Japanese flounder Paralichthys olivaceus in the central Seto Inland Sea having insufficient availability of mysids, Nipponomysis ornata and Iiella oshimai. We examined daily growth rates of wild juveniles; this measure can be used as an index of quality of a nursery. Juveniles consumed not only mysids, but also Crangon uritai and fishes. Mysid availability was lower at the study beach than in the nursery in the Sea of Japan; however, mean growth rates (MGRs) from May to June varied from 0.75 to 1.84 mm day−1 and equaled that in the nursery with sufficient availability of mysids in the Sea of Japan. Prey availability was high from May to June and decreased after July. Additionally, water temperatures after late July were higher than the optimal temperature. Multiple regression analysis suggested that the low availability of prey and high water temperatures reduced the MGR after July. The results indicate that the optimal season for releasing hatchery-reared juveniles is from May to June, a period characterized by high availability of prey. © 2014, Japanese Society of Fisheries Science.

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