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Knowledge about the genetic adaptations of various organisms to heterogeneous environments in the Northwestern Pacific remains poorly understood. The mechanism by which organisms adapt to temperature in response to climate change must be determined. We sequenced the whole genomes of Sillago japonica individuals collected from different latitudinal locations along the coastal waters of China and Japan to detect the possible thermal adaptations. A total of 5.48 million single nucleotide polymorphisms (SNPs) from five populations revealed a complete genetic break between the China and Japan groups. This genetic structure was partly attributed to geographic distance and local adaptation. Although parallel evolution within species is comparatively rare at the DNA level, the shared natural selection genes between two isolated populations (Zhoushan and Ise Bay/Tokyo Bay) indicated possible parallel evolution at the genetic level induced by temperature. Our result proved that the process of temperature selection on isolated populations is repeatable. Additionally, the candidate genes were functionally related to membrane fluidity in cold environments and the cytoskeleton in high-temperature environments. These results advance our understanding of the genetic mechanisms underlying the rapid adaptations of fish species. Projections of species distribution models suggested that China and Japan groups may have different responses to future climate changes: the former could expand, whereas the latter may contract. The results of the present population genomic work expand our understanding of genetic differentiation and adaptation to changing environments.

We investigated fish species composition seasonally at the intake and discharge of Weolseong Nuclear Power Plant (WS-NPP) from February to November 2008 using a trammel net. At the intake, 121 individuals belonging to 28 spe -cies were collected, and 157 fish from 34 species were sampled at the WS-NPP discharge. Dominant species at the intake were Chelidonichthys spinosus (17.2%), Scomber japonicus (11.5%) and Ditrema temminckii (8.2%) at the in- take, while Sillago japonica (18.5%), Chelidonichthys spinosus (13.4%) and Konosirus punctatus (8.3%) dominated at the discharge. The species count and diversity index at the discharge were highest during winter, whereas those at the intake were highest during spring, perhaps due to warm seawater at the discharge site. This study is the first to reveal an effect of effluent water on the aggregation of warm water fish species during winter.

Climate change is one of the most serious global environmental problems and it is of great importance to understand how species respond to climate change. Species distribution models (SDMs) have been regarded as an effective tool to examine the impacts of climate change on species’ potential distribution. In this study, we developed a SDM for a marine fish, the Japanese whiting Sillago japonica by using records of its occurrence and five predictor variables (ocean depth, distance to shore, mean sea surface temperature, salinity, and currents velocity) and predicted its habitat suitability for current conditions and under scenarios of future climates. The SDM suggests that ocean depth, distance to shore, and temperature are the three most important predictor variables determining the distribution of S. japonica. Our SDM accurately predicted the current distribution of the species, with values of true skill statistics and area under the receiver operating characteristic curve above 0.95. Under future climate scenarios, the suitable habitat of S. japonica is predicted to become smaller in size and to shift northward. Differences between climate change scenarios for 2040–2050 and 2090–2100 showed that this species will lose more suitable habitat as climate change progresses over time. Future fisheries management strategies should take this range contraction and associated northward shift into account.

Japanese whiting (Sillago japonica) is a relatively common marine fish inhabiting in the coastal shallow waters and the target species in an important commercial and recreational fishery. In this study, eighty-three specimens in five sites were collected along coasts of China and Japan, and genotyping-by-sequencing (GBS) technology was carried out to investigate the genetic structure and difference among them. Consistent with prior research conclusions, a relatively high genetic diversity was detected in S. japonica, and an increasing tendency of genetic variation level was detected as the latitude decreased in Chinese populations. Although estimated value of pairwise population differentiation (FST) was low, the genetic heterogeneity analysis demonstrated a certain amount of genetic differentiation among local populations of S. japonica. Samples from Rushan were differentiated from other Chinese populations, but closely correlate with Ise Bay (IB) and Tokoy Bay (TB) populations, indicating gene flow between Rushan population (RS) and Japanese populations to a certain extent. Isolation by distance (IBD) analysis showed that genetic differentiation was significantly affected by geographical isolation. While, the results of isolation by environment (IBE) test showed that genetic distance was correlated with seawater salinity, which might be a selective pressure promoting genetic variation in S. japonica. Given the complex pattern of genetic differentiation of Japanese whiting among Chinese and Japanese populations, we suggested treating them as different management units in utilization of offshore fisheries resources.

Prey selection by marine fishes is highly dependent on whether available food resources are abundant or deficient in their feeding grounds. The influence of fishing method on prey choice was analyzed via stomach content analyses of three coastal fishes: Pennahia argentata, Sillago japonica, and Thryssa kammalensis. Fish samples were collected from northern Jinju Bay, Korea, using two types of fishing gear that covered two different fishing layers in the water column: beam-trawl (bottom layer) and set-net (surface layer). When caught via beam-trawl, all three target species were function as bottom-feeding carnivores that consumed mainly benthic crustaceans and other invertebrates. In contrast, when caught via set-net, teleosts were the most abundant prey items in the diets of the three species. Significant differences in the diet composition between beam-trawl and set-net samples were revealed using permutational multivariate analysis of variance. Although seasonal changes in diet composition were also evident, the influence of season was weaker than that of fishing gear. Consequently, in this study, stomach content analysis demonstrated that set-net made a strong effect on prey selection by the co-occurring P. argentata, S. japonica, and T. kammalensis in southern Korean waters.

Live food resources are useful for larval fish rearing. However, production of sufficient live food resources is expensive. This study employed a cost-effective rotifer culture technique using fish waste diet (FWD) and investigate the effect of the FWD-fed rotifer on larval rearing of the Japanese whiting,Sillago japonica. Fertilized eggs ofS. japonicawere hatched in polycarbonate tanks containing 100 l of artificial seawater at 10 eggs l-1with 50 ml min-1of aeration at room temperature. Two diets (i.e. FWD-fed rotifers and rotifers fed with super fresh Chlorella-V12 as control) were used with 10 rotifers ml-1for 10 days. Fish were sampled every two days for morphometric and gut content analysis. Fatty acid analysis was done for both rotifers and fish larvae. The fish larvae fed with FWD-rotifers had higher total length than those given control diet. There was no significant difference in survival rate, viability, dry weight, gut content, head length, eye diameter, and body depth between the two diets. The DHA recorded of total lipid for the fish given FWD-rotifer and control fish are3 5.2% and 18.2% respectively. The use of waste-fed rotifers is cost-effective method to enhance the production of larval fish rearing in hatcheries.

Japanese whiting (Sillago japonica) is a commercially important demersal fish distributed along the coasts of East Asia and becomes recently an aquaculture species. Despite its commercial importance, the levels and patterns of population genetic variation remain poorly understood. In this study, 346 specimens were collected from 14 localities along the coastal waters of China, Korea and Japan and their genetic variation was analyzed with mtDNA control region (D-loop) sequences. A total of 131 polymorphic sites were detected which determined 294 haplotypes. A pattern with high levels of haplotype diversity (h = 0.999 ± 0.001) and nucleotide diversity (л = 0.030 ± 0.015) was detected in the examined range. Analyses of analysis of molecular variance (AMOVA) and F

Cryopreservation of fish embryos requires the swift uptake of considerable amounts of cryoprotectant (CPA) but this process is hampered by the low permeability of the egg chorion. This study examined the relative efficiency of ultrasound to promote the incorporation of CPAs in two different embryonic developmental stages (somites and tail elongation) of Japanese whiting Sillago japonica and performed a preliminary cryopreservation trial using the best conditions determined during the study. Embryos tolerated ultrasound densities up to 37.5 W/cm2 well for up to 3 min but had significant mortality at 50 W/cm2. Hatching rates of somites embryos sonicated at 37.5 W/cm2 for 1-3 min in 10 and 20% Me2SO solutions were comparable (61-72%) to that of sonication in artificial seawater (65-86%) but decreased sharply at the concentration of 30% (0-55%); at similar conditions, tail elongation embryos had comparatively lower survival. Me2SO content of sonicated embryos at the somites and tail elongation stages increased significantly by 58-191% and 27-123%, respectively, compared to controls exposed to Me2SO without ultrasound. Pre-exposure to Me2SO before sonication increased the CPA uptake further by 36% without impairing survival. A preliminary cryopreservation trial after ultrasound-mediated impregnation of somites embryos with a CPA solution containing 20% PG and 10% MeOH did not yield live embryos after freeze-thawing but resulted in a significant decrease of nucleation temperature and increase of the proportion of morphologically intact embryos after freeze-thawing. These results suggest that sonication might be useful for fish embryo cryopreservation although it may require combination with other techniques to enhance CPA permeation.

Twenty-four dinucleotide microsatellite DNA markers were developed for a commercially important fish, Japanese sillago (Sillago japonica). Loci were screened in 24 individuals from Laizhou Bay, China. The number of alleles per locus ranged from 7 to 24, and the observed and expected heterozygosity ranged from 0.333 to 0.913 and from 0.744 to 0.963, respectively. These microsatellites will facilitate the study of population-level variability (the genetic diversity and population structure) of S. japonica.

Sillago sihama (Forsskal, 1775), a commercially important marine fishery species in the Indo-West Pacific, is being developed as a target species for aquaculture and stock enhancement in China. However, due to the limitations of traditional isolation methods, the available microsatellite loci, or simple sequence repeats (SSRs), of S. sihama lack diversity. We used a stepwise approach including Illumina sequencing, primer screening, and SSR marker validation to develop diverse SSRs for S. sihama. A total of 853.48 Mb clean sequences were assembled with high coverage and sequencing depth, and 27,288 potential SSRs were identified. A set of 18 novel SSR markers with four type motifs including 11 di-, 1 tri-, 5 tetra-, and 1 hexanucleotide repeats were successfully isolated. The ranges of number of alleles per locus and observed and expected heterozygosities were 5-24, 0.226-0.968, and 0.319-0.950, respectively. The diversity parameters exhibited high levels of polymorphism in these 18 loci. Three loci with the presence of both null alleles and inbreeding showed significant deviation from Hardy-Weinberg equilibrium after Bonferroni correction. Moreover, 13 loci developed in S. sihama showed high transferability to the closely related species Sillago japonica. The polymorphic SSR markers developed in this study may serve as valuable tools for further basic and applied research on the genetic resources of S. sihama as well as S. japonica. Our results indicate that this approach, based on next-generation sequencing technology, is convenient, cost-effective, and suitable for SSR marker isolation in other sillaginid fishes.

Seasonal variations in species composition and abundance of the fish assemblages in the coastal waters off Gadeok-do were determined using monthly sample collection by a small otter trawl in 2010-2011. Of a total of 65 fishes collected, the dominant species were Leiognathus nuchalis, Clupea pallasii, Thryssa kammalensis, Engraulis japonicus, Repomucenus valenciennei, Sillago japonica, Trachurus japonicus, Pennahia argentatus, Okamejei kenojei, Cynoglossus joyneri, Pholis fangi, Pleuronectes yokohamae, and Zoarces gillii. These 13 fishes accounted for 92.8% of the total number of individuals collected. The number of fish species, number of individuals, biomass, and species diversity indices fluctuated with the seasons. The peak number of fishes occurred in April, whereas the biomass of fishes was highest in August. The numbers and biomass of fishes were lower in February corresponding with the low temperatures, and diversity indices were lower in January than in any other month.

Coastal marine ecosystem plays important role of spawning and nursery grounds for fisheries resources. Yongil Bay is one of major coastal marine ecosystems, which is located in the southwestern East Sea of Korea. Species composition and abundance of marine organism in the Yongil Bay were investigated by season from March to November 2009. Gill net and pot fisheries were used for survey of pelagic and demersal species composition, and collected 106 species, 67 families, and 7 taxa of fisheries resources from the coastal ecosystem. Species were included 2 species in Ascidiacea, 2 species in Bivalvia, 6 in Cephalopoda, 22 in Crustacea, 5 in Echinodermata, 12 in Gastropoda, and 57 in Pisces. Diversity indices (Shannon index, H') showed seasonal variation with low value of 2.11 in winter, and high value of 2.63 in autumn. Main dominant species were Asterias amurensis, Pleuronectes yokohamae, Siphonalia spadicea fuscolineata, Trachurus japonicas, Sillago japonica, Conger myriaster, Volutharpa ampullaceal, Engraulis japonicus, Asterina pectinifera, and Portunus (Portunus) sanguinolentus that were occupied over 71.5% of total individuals, and 52.9% of wet weight. Seasonal variations of fisheries resources composition were discussed on correlationships with those of environmental factors in the coastal ecosystem of the Yongil Bay in Korea. Those results from this study will provide scientific data and information to develop the ecosystem-based coastal fisheries assessment and management system in Korea.

Changes of fish assemblage inhabiting around Dae Island in Gwangyang Bay, Korea were investigated using a small beam trawl monthly from March 2009 to February 2010. These data were compared with those obtained in previous studies(1990~1991 and 1995~1996) at our study sites. A total of 8,133 fish belonging to 74 species in 38 families were collected. Leiognathus nuchalis, Argyrosomus argentatus, Acentrogobius pellidebilis, Sillago japonica, Apogon lineatus, Thryssa hamiltoni, Repomucenus richardsonii, Pholis nebulosa, Pleuronichthys cornutus, Hexagrammos otakii, and Limanda yokohamae dominated, and these were responsible for 89.5% and 58.9% in the number of individuals and in biomass, respectively. These were primarily small species or early juveniles of larger species. Seasonal variation in both species composition and abundance was large: the peak number of fish species occurred in May and October 2009, whilst both number of individuals and biomass were the highest in May 2009. Fish numbers as well as biomass was lowest in January and February 2010. Seasonal changes in the abundance of fishes corresponded with temperature. Compared with the previous studies, the total number of individuals and biomass per unit area(㎡) were higher, and the predominance of L. nuchalis occurred while abundances of Liparis tanakai were significant decreased. These results seemed to be change of species composition in fish assemblage which was due to variation of annual environmental characteristics in Gwangyang Bay.

Fish larvae were collected monthly with an ichthyoplankton net from 18 stations (including four stations located in eelgrass beds) in Gamak Bay and Yeoja Bay, southern Korea, in 2007. In total, 33 species of fish larvae were collected, of which Engraulis japonicus (48.5%), Tridentiger trigonocephalus (21.5%), and Omobranchus elegans (9.2%) were dominant. Dominant species varied seasonally: Hexagrammos otakii during December and January, Pholis nebulosa during January and March, Acanthogobius flavimanus in April, T. trigonocephalus in May, E. japonicus during June, July, September, and November, and Sillago japonica in August. Dominant species also differed between sites inside and outside the bays. Leiognathus nuchalis, O. elegans, and T. trigonocephalus were more abundant inside, while H. otakii was more abundant outside. From cluster analysis, three groups were identified according to sampling months (January-April, MaySeptember, and October-December) and two groups according to station (inside and outside bays). The occurrence of small larvae of almost all major fish species indicated that the bays were used as spawning and nursery grounds. An exception was Lateolabrax japonicus, whose specimens were relatively large (>19 mm TL), suggesting that this fish may spawn offshore, with its juveniles approaching the bays with growth.

Species composition and seasonal variation of fish assemblage in Sacheon marine ranching, Korea were examined. Sampling was seasonally made by a shrimp trawl from February 2009 to November 2009. A total of 55 species were collected. Of these, five species was dominant species comprising 51.1% of the total number of individuals. Nine species represented 57.3% of the total biomass. While total abundance (number of individuals) was high in spring, total biomass and species richness (number of species) and diversity were high in autumn. Cluster analysis, based on seasonally abundance data of the 21 most common species, showed that the species were separated into 4 different groups. Group A composed of Pholis nebulosa, Pleuronectes yokohamae, Hypodytes rubripinnis, Hexagrammos otakii, Tridentiger trigonocephalus and Paracercis sexfasciata, which were year round residents, group B Congr myriaster, Leiognathus nuchalis, and Platycephalus indicus, which were abundant in autumn, group C Sillago japonica, Pseudaesopia japonica, Zoarces gilli, Pholis fangi, and Pleuronichthys cornutus which were abundant in spring, and group D Sillago sihama, Cociella sp., Johnius grypotus, Cynoglossus joyneri, Cynoglossus robustus, and Pennahia argentata, which were abundant in summer. Principal component analysis revealed that seasonal variation in the fish assemblage was attributed to the abundance of temporal species such as conger and sand smelt fishes, which were abundant in summer, due to seasonal variation of water temperature.

To clarify the feeding habits and major food sources of sandy beach fishes, the gut contents of 55 fish species collected on a sandy beach at Fukiagehama, South-West Kyushu Island, Japan, were examined. Ontogenetic changes in food preference were recognized in nine species (Hypoatherina valenciennei, Lateolabrax japonicus, Trachurus japonicus, Sillago japonica, Sphyraena japonica, Paralichthys olivaceus, Heteromycteris japonica, Paraplagusia japonica, and Takifugu niphobles). A cluster analysis based on dietary overlaps showed that the sandy beach fish assemblage comprised six trophic groups (mysid, amphipod, zooplankton, juvenile fish, terrestrial insect, and mollusk feeders). Of these, the first three groups were the most abundantly represented, whereas the last two were represented by only a single species. These results indicated that epibenthic macrofauna, such as mysids and gammaridean amphipods, and zooplankton, were important food resources for the fish assemblage at the study site, but infaunal macrobenthos, such as polychaetes and bivalves, being relatively unimportant.

We examined shrimp and bycatch species composition in the shrimp beam trawl fishery off Wan-do, Korea(in the major or fishing ground)from December 2004 to November 2005. We observed a total of 103, 072 individuals in 96 taxa. By densities of individuals, 96.97% were shrimps, 1.20% decapods, 1.10% fish, 0.30% cephalopods and 0.43% other species. By catch weight, 57.29% were shrimps, 26.33% fish, 6.82% decapods, 4.64% cephalopods and 4.92% other species. In spring, the dominant bycatch species by biomass were Okamejei kenojei, Lophiomus setigerus, and Charybdis bimaculata. In summer, the dominant species were Charybdis bimaculata, Muraenesox cinereus, and Paralichlhys olivaceus. In autumn, dominants were Okamejei kenojei, Conger myriasler, and Sefipinna tenuifilis, and in winter they were Okamjei kenojei, Chaeturichthys stigmatias, and Sillago japonica. Bycatch species composition and individual species abundances differed significantly among seasons, probably indicating that variations were related to the life history characteristics of bycatch species. The diversity index was highest in October (2.797) and lowest in July (1.012). The July dominance index (0.569) was much higher than in other months; evenness was highest in September (0.856) and lowest in July (0.374). During the study period, the bycatch-to-shrimp ratio of this fishery varied from 0.063 in February 2005 to 11.031 in May 2005, with a mean of 3.363 These temporal variations may be linked 10 variations in reproductive behaviors and migration patterns of the marine animals sampled.

We aim to understand the relationships between physical conditions and characteristics of the immature-fish community in surf zones of sandy beaches. Therefore, we obtained fish samples between March 2007 and February 2008 and analyzed certain physical conditions in the surf zones of 21 sandy beaches on the coastline of the northwestern Kyushu Island, Japan. We collected a total of 83 species and 6458 immature individuals. In a BIO-ENV analysis, the highest correlation was observed between fish assemblage and S20 (i.e., the slope from the shoreline to the sites where the depth was 20 m) and current velocity (CV) values. Stepwise multiple linear regression analyses revealed that the number of species and individuals decrease with an increase in the S20 and CV values. These results show that species richness and the abundance of immature-fish increase under shelving and calm conditions. Thus, immature-fish assemblages are strongly influenced by the prevailing physical conditions. Moreover, in six of the 10 dominant species, a negative correlation was observed between CV and abundance. On the other hand, S20 was found to be the explanatory variable only in the case of the most dominant species, i.e., Gymnogobius breunigii. Furthermore, a positive correlation was observed between S1 (i.e., the slope from the shoreline to the sites where the depth was 1.0 m at the mean tidal level) and median particle size (i.e., MPS of the sediments) and the abundances of Sillago japonica and Favonigobius gymnauchen, respectively, and a negative correlation with salinity, in the case of Acanthogobius lactipes. We conclude that the characteristics of the fish community in surf zones on sandy beaches are determined by not only the shelving and calm conditions, which influence fish assemblages and abundances, but also the habitat diversity, which influences the diversity of fish species.

シロギス雄の血中ビテロゲニン（Vg）量に及ぼす成熟雌の影響を明らかにするために，産卵期のシロギスを用いて雌雄混合（混合区）と雄単独（単独区）の 2 群を設けて 3 週間飼育した後，各区の魚を 4 時間間隔で取り上げて，血清 Vg 濃度，生殖腺体指数（GSI），精巣組織を調べた。その結果，混合区の雄の血中 Vg 濃度は単独区よりも高かった。また両区の雄はともに活発な精子形成を行っていたが，混合区の雄の GSI は単独区よりも高かった。以上より，成熟雌の存在が雄の血中 Vg 濃度や GSI の上昇の要因になることが明らかとなった。

We cloned a full-length cDNA encoding vitellogenin (VTG) from a marine teleost, the Japanese sillago Sillago japonica. The cloned sillago VTG contained signal peptide, lipovitellin heavy chain, phosvitin, lipovitellin light chain, and beta'-component in the order from the N-terminus. An exposure to 17beta-estradiol significantly increased the levels of plasma VTG, but not hepatic VTG mRNA in males. Neither plasma VTG nor hepatic VTG mRNA levels were affected by the exposure to 4-tert-octylphenol. Hepatic VTG mRNA levels in males increased at 1 day after intraperitoneal administration of 17beta-estradiol but decreased in the subsequent 5 days. However, plasma VTG levels remained high for 5 days after administration, suggesting that the accumulation period of plasma VTG is longer than that of hepatic VTG mRNA in males. Therefore, VTG mRNA may be a suitable indicator of temporal exposure to estrogenic chemicals in the environment, whereas plasma VTG is useful to detect consecutive exposure.

To clarify the feeding habits of fishes in surf zones, the gut contents of 19 fish species collected in the surf zone of a sandy beach at Sanrimatsubara, western Japan, were examined. Ontogenetic changes in food preference were recognized in seven species (Mugil cephalus cephalus, Lateolabrax latus, Sillago japonica, Paralichthys olivaceus, Paraplagusia japonica, Takifugu poecilonotus, and Takifugu niphobles). A cluster analysis based on dietary overlaps showed that the surf zone fish assemblage comprised six trophic groups (zooplankton, benthic and epiphytic crustacean, detritus, polychaete, fish, and insect feeders). Of these, the most abundant trophic group was zooplankton feeders, along with benthic and epiphytic crustacean feeders.

Small-scale sillago, (Sillago parvisquamis) form the basis of a traditional recreational fishery in Japan. Historically distributed across a wide range, this species is now limited to a single population in the southwest region of the Suonada Sound in the Seto Inland Sea, Japan. Eleven candidate microsatellite loci were isolated from a small insert genomic DNA library of S. parvisquamis. In a screen of 40 individuals from Buzen Sea, we identified polymorphisms at all loci with levels of variability ranging from 2 to 20 alleles with no evidence of linkage disequilibrium. Observed heterozygosities ranged from 0.45 to 0.95, with no locus exhibiting significant departure from Hardy–Weinberg equilibrium. A test for cross-amplification with Sillago japonica revealed a subset of seven polymorphic loci that were successfully amplified. The polymorphic microsatellite loci developed in the current study will facilitate conservation genetic studies in both species, particularly the endangered S. parvisquamis.

We carried out dietary analysis on five numerically abundant fishes, Sillago japonica, Ditremma temmincki, Tridentiger trigonocephalus, Hippocampus japonicus and Petroscirtes breviceps in an eelgrass bed in Kwangyang Bay, Korea. Comparisons between species demonstrated that the dietary composition of each fish species was significantly different from that of every other species. Although gammarid amphipods and caprellid amphipods were consumed by all species, their individual contributions to each species' diet varied. Furthermore, polychaetes contributed to the diets of S. japonica and T. trigonocephalusand crab larvae were consumed byD. temmincki. Algae and eelgrass were not consumed by four fish species and made only a minimal contribution to the diet of P. breviceps. The diet of each fish species except H. japonicus underwent size-related changes; smaller fishes consumed gammarid amphipods, mysids and copepods, while larger fishes ate polychaetes, gastropods, isopods and other fishes. Differences in the prey organisms consumed of each individual species could be often related to differences in mouth length and width. S. japonica, D. temmincki, T. trigonocephalus, and P. breviceps underwent also a significant diel changes that could be related to differences in foraging behavior and/or prey availability. Thus, use of vision to detect prey would account for the greater daytime consumption of copepods by S. japonica and of crab larvae by D. temmincki, whereas the nocturnal emergence of gammarid amphipods, polychaetes and isopods from the substrate explained their greater consumption by S. japonica, D. temmincki, T. trigonocephalusand P. breviceps at night. Dietary breadth was greater for species with larger mouth dimensions.

Feeding habits of Sillago japonica collected from in an eelgrass (Zostera marina) bed in Jindong Bay, Korea were studied. S. japonica was a carnivore which consumed mainly gammarid amphipods, polychaetes, bivalves, caridean shrimps and crabs. Its diets also included a small amount of fishes, copepods and caprellid amphipods. The diet of S. japonica underwent significant size-related changes; small individuals ( 10 cm SL) ate polychaetes, caridean shrimps and crabs. The dietary breadth of S. japonica were varied with size. The diet of S. japonica also underwent seasonal changes that could be related to differences in prey availability; gammarid amphipods were mainly consumed in spring and polychaetes in summer.

Ocean sequestration of CO2 is proposed as a possible measure to mitigate climate changes caused by increasing atmospheric concentrations of the gas, but its impact on the marine ecosystem is unknown. We investigated the acute lethal effect of CO2 during the early developmental stages of four marine teleosts: red sea bream (Pagrus major), Japanese whiting (Sillago japonica), Japanese flounder (Paralichthys olivaceus), and eastern little tuna (Euthynnus affinis). The percentages of larvae that hatched and survived were not affected by exposure to water with a PCO2 of 1.0 kPa (= 7.5 mmHg) within 24 h. Median lethal PCO2 values for a 360-min exposure were 1.4 kPa (cleavage), 5.1 kPa (embryo), 7.3 kPa (preflexion), 4.2 kPa (flexion), 4.6 kPa (postflexion), and 2.5 kPa (juvenile) for red sea bream; 2.4 kPa (cleavage), 4.9 kPa (embryo), 5.9 kPa (preflexion), 6.1 kPa (flexion), 4.1 kPa (postflexion), and 2.7 kPa (juvenile) for Japanese whiting; 2.8 kPa (cleavage) and > 7.0 kPa (young) for Japanese flounder; and 11.8 kPa (cleavage) for eastern little tuna. Red sea bream and Japanese whiting of all ontogenetic stages had similar susceptibilities to CO2: the most susceptible stages were cleavage and juvenile, whereas the most tolerant stages were preflexion and flexion. © 2003 Wiley Periodicals, Inc. Environ Toxicol 18: 375–382, 2003

Because blood vitellogenin (Vg) has been considered a biomarker for environmental estrogens, the basal levels of Vg and 17β-estradiol (E2) were determined in male Japanese whiting reared under natural conditions. Serum levels of Vg and E2 were measured and gonadal development was assessed by gonadosomatic index (GSI) and histological observation in 8–10 male fish at monthly intervals throughout the annual reproductive cycle. Serum E2 was 1%. Histological observation revealed that testes in such male fish were in active spermatogenesis and then all of the testes of male fish in which serum Vg decreased to ND levels were regressed. These results suggest that Vg productive potency (sensitivity to estrogens) may increase in the spermatogenic stage, resulting in production of Vg in response to very low levels of natural or xenobiotic estrogens.

1999年4月～2001年3月に館出湾の砂浜海岸砕波帯の汀線域と沖浜で小型地曳網によりシロギス仔稚魚を採集し,出現や食性等を明らかにした。出現は主に7～9月で,とくに沖浜で多かった(沖浜,14,106個体;汀線域,302個体)。しかし両者で体長差はなかった(沖浜,12.9±4.3mm ;汀線域,13.2±6.8 mm)。主な餌生物は,体長13.9mmまではカラヌス目であり,14.0mmで多毛網が,17.0mmではアミ目が加わった。出現状況や食性等から,砕波帯,とくに沖浜は,シロギス仔稚魚の重要な成育場と考えられた。

Fish communities comprising postlarval to early adult stages were studied in the surf zone of a protected sandy beach, with runnels and a low tide terrace, at Doigahama, Yamaguchi Prefecture, western Japan. One elasmobranch and 100 teleost species, represented by a total of 17 608 individuals (1·85–785 mm in TL), were collected by fine and coarse meshed beach seines from May 1994 to April 1999. Species richness, abundance and biomass were greater during the evenings as well as in the warmer seasons (May to October). Larval and smaller juvenile ichthyofauna (collected mainly by fine-mesh seine) was relatively poor compared to larger juvenile ichthyofauna (coarse-mesh seine). Tidal effect was observed in the fine-mesh seine samples, whereas no tide-related trends were evident in the coarse-mesh seine samples. Effects of time of the day and tide on the species diversities were not so evident in both seines. Dominant species were classified according to the developmental stages occurring in the surf zone, as follows: Type-I: Postlarval (transformation) stage ( Plecoglossus altivelis altivelis , Sardinops melanostictus , Enneapterygius etheostomus , Tripterygion bapturum , Luciogobius sp.). Type-II: Juvenile stage ( Lateolabrax latus , Trachurus japonicus , Gerres oyena , Acanthopagrus schlegeli , Sparus sarba , Girella punctata , Mugil cephalus cephalus , Paralichthys olivaceus , Tarphops oligolepis , Heteromycteris japonica ). Type-III: Postlarval and juvenile stages ( Spratelloides gracilis , Engraulis japonicus , Gobiidae sp.1). Type-IV: Juvenile and early adult stages ( Sillago japonica , Paraplagusia japonica ). Type V: Postlarval to early adult stages ( Takifugu niphobles ). It is considered that the surf zone at Doigahama functions as a nursery area, particularly as a feeding place for larger juveniles than as a shelter for larvae and smaller juveniles.

To determine the thermal limit for normal spawning of Japanese whiting and to evaluate thermal effects on spawning in the normal temperature range, two experiments were conducted. In Experiment 1, the temperature of three experimental groups (Groups A, B and C) was increased from 25 to 28, 31 or 33°C, respectively. Subsequently, temperatures in all groups were decreased to 28°C. During the experimental period, the number of eggs, egg size, and hatching rate were monitored. According to the results, the upper thermal limit of normal spawning was considered to be 28–29°C, because the number of eggs and the hatching rate decreased at temperatures over 28°C. However, egg size tended to be reduced at 28°C, and was found to be strongly dependent on temperature. In Experiment 2, the number of eggs, egg size and time of spawning were compared between fish held at a constant temperature of 22°C (Group CT) and those held at increasing temperatures from 22 to 28°C (Group IT). Group IT spawned more in number and had smaller-sized eggs than did Group CT, while spawning was delayed in group IT. To identify the thermal effects on spawning of Japanese whiting, the mechanisms governing egg size must be determined.

SUMMARY: The survival of Japanese whiting Sillago japonica and by-catch species captured by a sweeping trammel net was examined to assess the effects of differing species, captured conditions, and body lengths on survival, in Tateyama Bay, Chiba Prefecture, Japan. All the live samples were kept in laboratory tanks for 4 days of successive survival observation. The survival ratio of the Japanese whiting varied by the captured conditions. The fish captured by pocketed condition was 27% surviving at the fourth day, which was significantly higher than the gilled and entangled fish. Most of the by-catch species survived for 4 days. About 60% of dead Japanese whiting were observed to have scar injury and damage on the body surface. For the by-catch species, the body damage occurred only in stripedfin goatfish Upeneus bensasi, Temminck's surfperch Ditrema temmincki, and tidepool gunnel Pholis nebulosa. Therefore, it suggests that the conservation measure through catch-and-release may be an appropriate method for most by-catch species, but not for the Japanese whiting.

Ovarian developmental stages and serum steroid hormone levels were examined at six different times of day (0100, 0600, 1000, 1300, 1600, 2000 h) in a marine teleost, the Japanese whiting Sillago japonica, which has an asynchronous-type ovary containing oocytes at various stages of development and spawns every day during a period ranging up to three months. The largest oocytes in the ovaries at the active vitellogenic or post-vitellogenic stages were found between 0100 and 1300 h. Oocyte maturation indicated by germinal vesicle breakdown (GVBD) occurred at 1600 h, and ovulated oocytes were observed in the ovaries collected at 2000 h. These processes were accompanied by a significant daily change in serum steroid hormone levels. The serum level of estradiol-17β showed a peak in fish with mature oocytes sampled at 1600 h. In these fish, the second-largest oocytes in the ovaries were at the initial stage of vigorous vitellogenesis, the secondary yolk stage. Therefore the highest level of serum estradiol-17β was considered to be due to the second-largest oocytes. Testosterone levels remained low and constant throughout the experimental period. The serum levels of 17α,20β-dihydroxy-4-pregnen-3-one (17α,20β-diOHprog) peaked at 1600 h at which time all fish had mature oocytes. These results indicate that the Japanese whiting possesses a diurnal rhythm of oocyte development including vitellogenesis, oocyte maturation and ovulation, and further suggest that daily cycles in oocyte growth and maturation which simultaneously take place in an ovary are regulated by diurnal secretions of estradiol-17β and the maturation-inducing steroid, 17α,20β-diOHprog.

To determine the annual reproductive cycle of Sillago japonica in Ago Bay, the GSI (Gonado‐somatic index) investigation and histological observation of gonads were carried out every month from May 1997 to December 1998. In females, GSIs between June and September (>3) were higher than from October to May (0.5) were higher than between October and April (, 三重県英虞湾に産するシロギスの生殖周期を明らかにするため，1997年4月から1998年12月までの期間に毎月採集した生殖腺のGSI測定と組織学的観察を行い以下の点を明らかにした。1．雌のGSIは6～9月が高く，10～5月が低かった。卵巣の組織学的観察では，11～4月の卵巣はすべて未熟であった。5月に卵黄蓄積の開始が認められ，6～9月には多くの個体において成熟卵が認められた。退行卵は9～10月にかけて出現した。2．雄のGSIは5～9月が高く，10～4月が低かった。12～1月の精巣はすべて休止期であった。2月に精子形成の開始が認められ，3～4月には少量であるが精子も観察された。ただしこの間のGSIにははとんど変化が見られなかった。5～9月は多くの個体において精小嚢内腔と主輸精管内に精子が充満していた。後繁殖期の精巣は9月から出現し，10月に多くの個体において観察された。3．以上の結果から英虞湾産シロギスの生殖周期は，成熟の開始時期などにおいて雌と雄とでは異なっていたが，大量の成熟卵と精子が生産される本格的な配偶子形成は，雌雄ともに5～9月に集中的に行われていることが明らかになった。したがって，産卵期は6～9月と推定された。

SUMMARY: To determine the mesh selectivity of a sweeping trammel net for Japanese whiting Sillago japonica, experimental fishing operations using three different inner net mesh lengths (27.5, 31.0 and 33.5 mm) were carried out in Tateyama Bay, Chiba Prefecture, Japan from August to November 1996 and from April to May 1997. The length mode of captured fish increased in proportion to the mesh length from 150–160 mm of the smallest mesh to 190–200 mm total length of the largest mesh. The master curve of selectivity in terms of length ratio to the mesh length (l/m) showed a wide selection range of 50% relative efficiency compared to the mesh selectivity curve of gill net. The curve had a peak at l/m of 6.3 with the selection range from 5.4 to 7.4. This suggested that the trammel net caught a large number of entangled or pocketed fish in comparison to the gilled fish due to the effect of inner net slackness. In terms of body girth ratio to mesh perimeter (G/P), the curve had a peak at G/P of 1.31, which reflected that relative efficiency of capture reached its maximum when the body girth of fish was 1.31 times that of the mesh perimeter.