Classification of fish schools based on evaluation of acoustic descriptor characteristics     

Aymen Charef  Seiji Ohshimo  Ichiro Aoki  Natheer Al Absi 《Fisheries Science》2010,76(1):1-11

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Examination of a practical method for zinc enrichment of euryhaline rotifers (Brachionus plicatilis)     

Seiji Matsumoto  Shuich Satoh  Tomonari Kotani  Hiroshi Fushimi 《Aquaculture (Amsterdam, Netherlands)》2009,286(1-2):113-120

Larval growth and survival of marine finfish in mass seed production are affected by the nutritional value of live feeds such as rotifers and Artemia. Thus far, many studies have been conducted to develop effective methods for the enrichment of live feeds with essential fatty acids and vitamins. In this study, a practical method for enrichment of rotifers with zinc was investigated. Changes in the concentrations of other minerals when zinc was added to the rotifer-enrichment tanks were also studied. The mineral composition of rotifers and Chlorella after zinc enrichment revealed that the direct addition of zinc to the culture media was not effective because rotifers cannot efficiently accumulate waterborne zinc. The ability of Chlorella to absorb waterborne zinc is much higher than that of rotifers, and hence, zinc was pre-accumulated in Chlorella, which was then fed to the rotifers. The maximum zinc content of the rotifers was 585.0 μg g^? 1 (dry matter) when the rotifers were enriched with zinc alone. This zinc concentration is comparable to that found in natural zooplankton. In rotifers simultaneously enriched with zinc and n?3 highly unsaturated fatty acids (HUFAs), the zinc content increased, but the n?3 HUFA content did not. Therefore, separate enrichment with zinc and fatty acids was adopted. The zinc content of rotifers fed zinc-enriched Chlorella was significantly higher than that of rotifers fed unenriched Chlorella. After zinc enrichment, rotifers were enriched with fatty acids, and the docosahexaenoic acid (DHA) and n?3 HUFA levels in rotifers were higher than the levels obtained after simultaneous enrichment with zinc and fatty acids. With regard to the concentration of other minerals in rotifers after zinc enrichment, the manganese content tended to decrease when the zinc content increased.The results of this study demonstrated that zinc enrichment of rotifers was successfully performed by using microalgae that had accumulated zinc, and the enrichment of rotifers with fatty acids was also achieved after the completion of zinc enrichment and before feeding the larvae. This method could be utilized for the enrichment of zooplankton with other minerals as well.  相似文献   

Estimation of the spawning grounds of chub mackerel <Emphasis Type="Italic">Scomber japonicus</Emphasis> and spotted mackerel <Emphasis Type="Italic">Scomber australasicus</Emphasis> in the East China Sea based on catch statistics and biometric data     

Ryuji Yukami  Seiji Ohshimo  Mari Yoda  Yoshiaki Hiyama 《Fisheries Science》2009,75(1):167-174

The spawning grounds of the chub mackerel (Scomber japonicus) and spotted mackerel (Scomber australasicus) in the East China Sea were estimated based on catch statistics of the Japanese large- and medium-type purse seine fishery from 1992 to 2006. Biometric data were obtained from specimens caught by purse seiners in the East China Sea from 1998 to 2006. Gonadosomatic index (GSI) at 50% sexual maturity of chub mackerel and spotted mackerel females was 2.5 and 2.6, respectively. Using this criterion for GSI, chub mackerel larger than 275 mm and spotted mackerel larger than 310 mm in fork length were considered to be mature. Mature chub mackerel was observed in the area of 15–22°C sea surface temperature (SST), and mature spotted mackerel was observed in the area of 17–25°C SST. The spawning period of chub mackerel ranged from February to June, and that of spotted mackerel ranged from February to May in the East China Sea. The spawning grounds were estimated from the distributions of catch per unit effort (CPUE) of spawners and SST. As a result, the spawning ground of chub mackerel was estimated to be in the central and southern part of the East China Sea and the area west of Kyushu in February, March, and April, and in the central part of the East China Sea, the area west of Kyushu and Tsushima Straight in May, and in Tsushima Straight and western part of the Sea of Japan in June. The spawning ground of spotted mackerel was estimated to be in the central and southern part of the East China Sea and southern coastal area of Kyushu in February, March, and April, and the central and southern part of the East China Sea and the area west of Kyushu in May.  相似文献   

Food habits of fishes in a freshwater reed belt in Lake Kitaura,eastern Japan,in summer     

Seiji Usui  Kouki Kanou  Mitsuhiko Sano 《Fisheries Science》2018,84(3):469-476

The diets and feeding guild structure of a freshwater reed belt fish assemblage (30 species) were examined in Lake Kitaura, part of the Lake Kasumigaura system, eastern Japan, from June to September in 2009 and 2010. Ontogenetic dietary shifts were recognized in 14 species, including several species (e.g., Cyprinus carpio, Tridentiger brevispinis and Hyporhamphus intermedius) targeted by local fisheries. Juveniles of these species generally fed on zooplankton, later switching to other prey items (e.g., benthic chironomid larvae, gammaridean amphipods, shrimps, juvenile fishes, diatoms and decomposing reeds) with growth. A cluster analysis based on dietary overlaps showed that the reed belt fish assemblage comprised five feeding guilds (plant, zooplankton, benthic invertebrate, terrestrial insect and fish feeders). Of these, zooplankton feeders were the most abundantly represented in terms of species numbers, suggesting that the main food items for the fish assemblage were zooplankton (e.g., cladocerans, and calanoid and cyclopoid copepods). Fish feeders included five species, of which one was an alien species introduced from another region in Japan (Opsariichthys uncirostris) and three were from foreign countries (Micropterus salmoides, Lepomis macrochirus macrochirus and Ictalurus punctatus).  相似文献   

Habitat use and movement patterns of small (age‐0) juvenile Pacific bluefin tuna (Thunnus orientalis) relative to the Kuroshio          下载免费PDF全文

Ko Fujioka  Hiromu Fukuda  Seishiro Furukawa  Yaoki Tei  Suguru Okamoto  Seiji Ohshimo 《Fisheries Oceanography》2018,27(3):185-198

The habitat use of Pacific bluefin tuna (Thunnus orientalis; PBF) in nursery waters off the southern coast of Japan was investigated using archival tags over a 3 year study period (2012–2015), and the data were used to examine the free‐ranging habitat preferences of PBF and the relationship between their horizontal movements and the path of the Kuroshio off the Pacific coast of Japan. The path of the Kuroshio fluctuated seasonally, leading to changes in water temperature that strongly influenced the habitat use of small PBF (2–3 months after hatching). Most PBF were present in coastal waters inshore of the path of the current, and their habitat use changed in response to the distance of the current from the coast. The Kuroshio typically flowed along the coast from summer to autumn, and PBF remained in the coastal waters off Kochi Prefecture during this period. In contrast, PBF quickly moved eastward in winter when the current moved away from the coast. Throughout the winter and spring, the area of habitat use extended widely from the eastern end of the southern coast of Japan (the Boso Peninsula) to the offshore Kuroshio‐Oyashio transition region. These findings suggest that the seasonal habitat use and movement behavior of juvenile PBF are influenced by the distance of the Kuroshio axis from the coast, and the ultimate drivers are likely variations in oceanographic conditions and prey availability along the southern coast of Japan.  相似文献   

Relative abundance trend of the blue shark <Emphasis Type="Italic">Prionace glauca</Emphasis> based on Japanese distant-water and offshore longliner activity in the North Pacific     

Yuko Hiraoka  Minoru Kanaiwa  Seiji Ohshimo  Norio Takahashi  Mikihiko Kai  Kotaro Yokawa 《Fisheries Science》2016,82(5):687-699

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Two new species,Phytophthora nagaii sp. nov. and P. fragariaefolia sp. nov., causing serious diseases on rose and strawberry plants,respectively, in Japan     

Mohammad Ziaur Rahman  Seiji Uematsu  Toru Takeuchi  Kayo Shirai  Yasushi Ishiguro  Haruhisa Suga  Koji Kageyama 《Journal of General Plant Pathology》2014,80(4):348-365

A new disease of rose was noticed in Chiba Prefecture of Japan in 1968, and the pathogen was initially identified as Phytophthora megasperma based on morphological characteristics. Similar Phytophthora isolates have since been collected from rose plants in Chiba, Kanagawa, and Shizuoka Prefectures. In 2005, several Phytophthora isolates were recovered from crowns of strawberry plants in Hokkaido Prefecture. These were considered to be members of a new species. In this study, we re-examined all these isolates using morphological and physiological studies and a multilocus phylogenetic analysis. The rose and strawberry isolates were mostly similar morphologically and physiologically, with some exceptions. The rose isolates differed significantly from P. megasperma sensu stricto and other related Phytophthora species. The rose and strawberry isolates had external proliferation of sporangia, characteristic funnel-shaped oogonia, predominantly paragynous antheridia, and fast growth rates of 10.5 mm/24 h at an optimum temperature of 28 °C. In the multilocus phylogenetic tree constructed using sequences from the rDNA ITS regions, rDNA LSU, and the translation elongation factor 1-α, β-tubulin and coxI genes, they formed a distinct monophyletic group in clade 7 with strong bootstrap support. The rose and strawberry isolates separated into two distinct groups. The results indicate that the rose and strawberry isolates constitute two separate species, designated here as Phytophthora nagaii and P. fragariaefolia.  相似文献   

Anthracnose of sweet pepper caused by Colletotrichum scovillei in Japan     

Takeshi Kanto  Seiji Uematsu  Toshihide Tsukamoto  Jouji Moriwaki  Naho Yamagishi  Toshiyuki Usami  Toyozo Sato 《Journal of General Plant Pathology》2014,80(1):73-78

Severe fruit rot of sweet pepper was found in Shimane, Hyogo, Chiba, Toyama, and Nagano prefectures, Japan from 2005 to 2011. Dark, sunken spots with concentric rings of orange conidial masses appeared on fruits. Pathogenic isolates from diseased fruits in the prefectures were identified as Colletotrichum scovillei. This species was added to the pathogens of sweet pepper anthracnose in Japan. The representative isolate was pathogenic to sweet pepper, tomato and chili pepper fruits, kidney bean pod, azuki bean, pea and strawberry leaves, but a caused no symptoms on cucumber or carrot in inoculation tests.  相似文献   

Seasonal contribution of C3 and C4 species to ecosystem respiration and photosynthesis estimated from isotopic measurements of atmospheric CO2 at a grassland in Japan     

Seiji Shimoda  Shohei Murayama  Wenhong Mo  Takehisa Oikawa 《Agricultural and Forest Meteorology》2009,149(3-4):603-613

Measurements of δ¹³C in atmospheric CO₂ and plant samples were made in 2003, along with CO₂ flux measurements, at a grassland site in Tsukuba in central Japan. The objective of the study was to obtain estimates of relative seasonal contributions of C₃ and C₄ plants to the net CO₂ flux over a C₃/C₄ grassland area influenced by the Asian monsoon. C₄ contribution to the ecosystem respiration (f_4R) increased from June to September, and then became constant at 63–67% through October and November. The seasonal variation in f_4R reflected the biomass composition of C₃ and C₄ plants at the measurement site. The seasonal C₄ contribution to photosynthesis (f_4P) was significantly different from its contribution to f_4R in May (8%) while it showed similar values to f_4R after June. The seasonal variations in f_4R and f_4P reflect the biomass composition ratio. Such seasonal transition from C₃ to C₄ of relative contribution to the carbon flux is similar to that observed in humid prairie ecosystems, while it is different from that in dry prairie ecosystems where the contribution of C₃ plants is lower and the seasonal maximum of the C₄-plant contribution occurs earlier compared to the humid prairie ecosystems.  相似文献   

Genetic contribution of parents in sex determination of honmoroko Gnathopogon caerulescens     

Yasuhiro Fujioka  Seiji Ueno 《Fisheries Science》2014,80(5):943-950

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.  相似文献