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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.

Komatsu H.,Kagawa University | Fujiwara M.,Kagawa University | Miyagawa M.,Kagawa Prefectural Fisheries Experimental Station | Kakegawa H.,Kagawa University | Suenaga Y.,Kagawa University
Proceedings of the International Offshore and Polar Engineering Conference | Year: 2011

Recently, fishery products have been decreased in the Seto Inland Sea located at the western part of Japan. One of these reasons is decrease of seagrass and seaweed beds such as Zostera marina, Sargassum and so on. The valuable marine resources are using Zostera marina beds as spawning and nursery grounds. In this study, the authors reproduced the flow field around the Zostera marina bed behind the detached breakwater using three-dimensional hydrodynamical model. Then we examined the appropriate area of Zostera marina beds and new construction method of detached breakwaters for preservation of seagrass and seaweed beds. Copyright © 2011 by the International Society of Offshore and Polar Engineers (ISOPE).

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.

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.

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