Kareius Research Articles

Effects of constant and variable salinity regimes on the occurrence, feeding, and growth of two juvenile flatfishes (Pseudopleuronectes yokohamae and Platichthys bicoloratus)

Extreme environmental conditions, such as high and low salinity, are stressors for marine fish growth. Juveniles of marbled flounder Pseudopleuronectes yokohamae and stone flounder Platichthys bicoloratus use estuaries as nursery grounds. Our field surveys showed that the occurrence of juvenile stone flounder seemed to be unrelated to salinity, whereas that of juvenile marbled flounder was positively correlated with salinity. To examine the effects of salinity on feeding and growth of these species, we conducted a laboratory experiment in which juveniles were reared individually under constant and variable salinity regimes for seven days. Cultured marbled flounder of two sizes (23–29 and 48–58 mm standard length) were reared under constant salinities of 5, 15, and 30 and fluctuating salinities of 5–30 and 15–30 or 5–15. Wild stone flounder (23–37 mm standard length) were reared under constant salinities of 1, 5, and 30 and fluctuating salinities of 5–30 and 1–30. Commercial pellets were fed to fish twice daily until satiation. The feeding and growth of marbled and stone flounders were considerably low at constant salinities of 5 and 1, respectively. Meanwhile, suppression of feeding and growth was not observed in fish with salinities varying from 5 to 30 or 1 to 30, respectively. The results indicated that extremely low salinity inhibits feeding and growth of juveniles only with continuous exposure. Estuaries with fluctuating salinities are potential nursery grounds for both marbled flounder and stone flounder, although marbled flounder tend to avoid low-salinity environments in the field. This study showed that extremely low-salinity environments, which reduce juvenile growth when consistently exposed, would not affect distribution or growth if they were temporary around low tide.

A new concept for bycatch reduction in small-scale accordion-shaped trap fisheries of the Yellow Sea, China

The bycatch issue is a major concern in small-scale accordion-shaped trap fisheries in the Yellow Sea of China because of the poor species and size selectivity of fishing gear and the co-occurrence of multispecies. Two threatened flatfish species assessed by the IUCN, marbled flounder (Pseudopleuronectes yokohamae) and stone flounder (Platichthys bicoloratus), are the two main bycatches in accordion-shaped trap fisheries. This fishery also captures a large proportion of juvenile target species, resulting in both recruitment and growth overfishing of these species. In this study, we introduced a new concept of a combined sorting grid and escape vent (CSEV), a selection device aimed at reducing the bycatch of flatfish and undersized target species in mixed-species trap fisheries. We used a catch comparison method to assess the performance of the CSEV in field experiments, with conventional traps as the baseline. Our results demonstrated that the CSEV significantly improved the species and size selectivity of the traps. Test traps mounted with the CSEV significantly reduced the catch rates of marbled flounder and stone flounder by 70% and 74% throughout the length class, respectively, compared with conventional traps. The catch of undersized target species, namely, fat greenling (Hexagrammos otakii), black rockfish (Sebastes schlegelii), and Asian paddle crab (Charybdis japonica), was reduced by 79%, 75%, and 80%, respectively, while the catch rates of target-sized individuals were maintained or even improved. Given these promising results, the CSEV may have great potential for application in accordion-shaped trap fisheries and similar fisheries.

Application of light-emitting diodes (LEDs) fishing lights to improve catch rates of small-scale trammel net fishery in the Yellow Sea, China

The small-scale trammel net fisheries are essential to the economy and well-being of coastal communities in the Yellow Sea, China. However, these fisheries are low efficient and urgently demand technical innovations to improve catch rates. In this study, we conducted field experiments in three traditional fishing grounds (Rizhao, Yantai, and Weihai) to test whether the addition of different colored light-emitting diodes (LEDs) fishing lights in the trammel nets could improve the catch rates of seven commercial species. Results showed that the effects of LEDs on catch rates were species-specific. Green LEDs could significantly increase the catch per unit effort (CPUE) of black rockfish (Sebastes schlegelii), fat greenling (Hexagrammos otakii), marbled flounder (Pseudopleuronectes yokohamae), stone flounder (Platichthys bicoloratus), Asian paddle crab (Charybdis japonica), and mantis shrimp (Oratosquilla oratoria) by 40%-72% compared with unilluminated nets, while had no significant effect on the catch rates of swimming crab (Portunus trituberculatus). Red LEDs harvested 58%-86% higher CPUE of fat greenling, marbled flounder, stone flounder, mantis shrimp, and swimming crab while catching fewer black rockfish and Asian paddle crab. Blue and white LEDs exhibited similar performance, which could significantly capture more black rockfish, fat greenling, and mantis shrimp and did not affect the catch rates of other species. The effects of LEDs were also size-dependent for certain species, and the catch rates generally increased with the length classes. Taking economic benefits into consideration, the green and red LEDs provided the highest profitability for Rizhao, while green LEDs performed best in Weihai and Yantai. This study is the first investigation on how artificial lights affected the catch rates of trammel nets. The findings of our study illustrated that trammel nets equipped with LEDs could serve as a viable fishing strategy in small-scale trammel net fisheries.

Otolith isotopic characterization as a nursery habitat indicator for stone flounder Platichthys bicoloratus

Both estuarine and exposed inshore areas along the open coast have been known as important nursery grounds for some flatfish species belonging stone flounder Platichthys bicoloratus. To evaluate the usefulness for distinguishing the nursery habitat types according to different salinity conditions, we examined the otolith stable isotopic ratios (δ18Ootolith and δ13Cotolith) of juvenile stone flounder collected from four habitat types located around Sendai Bay, Miyagi Prefecture, as well as along the coastal areas of neighboring Fukushima Prefecture, northeastern Japan. Muscle tissue stable isotopic ratios (δ15Nmuscle and δ13Cmuscle) of fish used for otolith analyses were also measured for assisting in the interpretation of mechanisms involved in the variations in otolith values. The δ18Ootolith values were significantly different among individuals from different types of nursery habitat, likely reflecting salinity of each habitat, namely the value of individuals from the exposed inshore area being the highest, followed in order by those from brackish embayment, lagoon, and river mouth areas. These results suggest that the δ18Ootolith precipitated during the juvenile stage can be a reliable proxy to determine the habitat type experienced by each individual on nursery ground after settlement. The δ13Cotolith was associated with δ13Cmuscle. The δ13Cotolith was markedly different between exposed inshore and estuarine habitats, reflecting the difference in major food source organisms between those habitats. Those isotopic characteristics suggest that δ18Ootolith and δ13Cotolith analysis can provide additional information about nursery habitat type of stone flounder.

Effects of cryoprotective agents and treatment methods on sperm cryopreservation of stone flounder, Kareius bicoloratus

This study was performed as part of the effort to develop artificial seed production techniques for stone flounder Kareius bicoloratus, which has a great potential for farming in northeast Asian countries. To develop a sperm cryopreservation protocol that can be applied for artificial fertilization, we carried out experiments on the key factors for successful fish sperm cryopreservation, including cryoprotective agents (CPAs), diluents, equilibration times, and dilution ratios. The CPAs tested in this study were dimethyl sulfoxide (DMSO), glycerol, methanol, and ethylene glycol, and the diluents were glucose and sucrose. The equilibration times tested in the experiments ranged from 0 to 210 s and the dilution ratios ranged from 1:1 to 1:1000. According to the results of our experiments, the optimal CPA for stone flounder sperm cryopreservation was DMSO in concentrations ranging from 7.5% to 10% when 300 mM glucose was used as diluent and DMSO in concentrations ranging from 15% to 17.5% when 300 mM sucrose was used as diluent. Post-thaw sperm motility was high, with equilibration times up to 150 s, and dilution ratios up to 1:10 (semen:CPA + diluent) showed no significant differences in the effect on post-thaw sperm motility. The cryopreserved sperm showed more significant DNA damage than the fresh sperm with the severity of DNA damage being in inverse proportions to post-thaw sperm motility and survival rate. It is expected that these results will be useful for applications of artificial fertilization at stone flounder hatchery farms.

Seasonal bathymetric distributions of three coastal flatfishes: Estimation from logbook data for trawl and gillnet fisheries

The present study aims to clarify the Seasonal bathymetric distributions of three coastal flatfishes (stone flounder, marbled flounder, and Japanese flounder) that are caught mainly by bottom trawls and gillnets off the coast of Fukushima, Japan, by using logbook data. All three species were found to have specific spawning depths, i.e., depths of 40–80 m, 20–40 m, and 10–60 m for stone, marbled, and Japanese flounders, respectively, with extremely high catch-per-unit-effort during their spawning seasons, reflecting spawning ground formation. Furthermore, Japanese flounder showed a tendency to expand their distribution offshore to depths deeper than 100 m after October. These results indicate interspecific variations in migration and aggregation patterns. Using logbook data and considering the seasonal catchability of each fishing gear enabled us to understand the seasonal bathymetric distribution of each species and the depths of their spawning grounds.

Development of Allotriploid Embryos Produced by Crossing Female Starry Flounder Platichthys stellatus and Male Stone Flounder Kareius bicoloratus

We investigated the development of allotriploid embryos derived from a cross between female starry flounder Platich thys stellatus and male stone flounder Kareius bicoloratus. The second cleavage, mid-blastula, gastrula, and Kupffer’s vesicle appearance stages, and hatching of embryos began 3.7, 25.6, 45.7, 87.7, and 213.2 h after cold shock at 6°C, respectively. The hatching and development time of triploid interspecific hybrid eggs was approximately the same as those of diploid starry flounder eggs at the same incubation temperature.

Ultrastructural Studies on Oocyte Differentiation and Vitellogenesis in the Oocytes of Female Kareius bicoloratus in Western Korea.

Ultrastructural studies on oocyte differentiation and vitellogenesis in the oocytes of female Kareius bicoloratus were investigated by transmission electron microscopy. The Golgi complex in the cytoplasm is involved in the formation of yolk vesicles that contain yolk carbohydrates in the yolk vesicle of oocytes in the early vitellogenic phase. In this phase, many pinocytotic vesicles (PVs), which are formed by pinocytosis, contain yolk precursors (exogenous substances). These substances are associated with exogenous heterosynthetic vitellogenesis. In yolked oocytes in the late vitellogenic phase, two morphologically different bodies, which formed by modified mitochondria, appear in oocytes. One is a multivesicular body (synthesized by autosynthetic vitellogenesis), and the other is a yolk precursor (an exogenous substance formed by heterosynthetic vitellogenesis). The multivesicular bodies (MVB) are taken into the yolk precursors (YP) and are transformed into primary yolk globules. However, after the YP mix with exogenous PVs near the zona pellucida, they are transformed into primary yolk globules. Vitellogenesis of this species occurs via endogenous autosynthesis and exogenous heterogenesis. Vitellogenesis occurs through endogenous autosynthesis, which involves the combined activity of the Golgi complex, mitochondria and MVB formed by modified mitochondria. However, heterosynthesis involves pinocytotic incorporation of extraovarian precursors (such as vitellogenin in the liver) into the zona pellucida (via granulosa cells and thecal cells) of the yolked oocyte.

English

The Tokyo Electric Power Company's, Fukushima Dai-ichi nuclear power plant in Fukushima-Ken (Fukushima Prefecture), Japan, was destroyed in March 2011 by a massive magnitude 9 earthquake (centred offshore to the northeast of Honshu Island) and by the subsequent historic Tsunami of March 11, 2011. Because of the nuclear meltdown, hydrogen-explosion damage to the buildings that housed the reactors, and the contamination of the cooling water from the reactor cores, large quantities of radioisotopes were emitted into the atmosphere and adjacent seawater. The Tokyo University of Marine Science and Technology has measured radioisotope levels in fishery species off Iwaki-Shi(Iwaki City), Fukushima-Ken (located south of the former nuclear power plant); these data could be used to understand the relationship between the accumulation of specific nuclides (radioisotopes) and certain species of fish, as follows: [1] It is possible to accumulate or separate specific nuclides (134Cs and 137Cs) by combining Sebastes cheni (Japanese rockfish; SHIROMEBARU) and Kareius bicoloratus (Stone flounder; ISHIGAREI), and Ditrema temmincki temmincki (Surfperch; UMITANAGO) and Cynoglossus joyneri (Red tongue sole; AKASHITA BIRAME). [2] There are differences in 134Cs and 137Cs accumulation between adult fish and fry of Paralichthys olivaceus (Bastard halibut; HIRAME). Therefore, some fish species have the ability to accumulate a specific nuclide (radioisotope). To date, ultra-centrifugation and diffusion methods have been used to accumulate specific nuclides for atomic fuel. However, if we could use the ability of some fish species to accumulate specific nuclides, we would have additional methods to concentrate nuclides. Key Words: Nuclide, Accumulate, Fukushima, Fish.

Morphological characteristics and distribution of Pleuronectidae (Pisces) eggs in the western margin of the East Sea

Seven species of Pleuronectidae (Platichthys stellatus, Kareius bicoloratus, Pseudopleuronectes herzensteini, Microstomus achne, Glyptocephalus stelleri, Hippoglossoides dubius, and Limanda punctatissima) were identified based on eggs collected from the western margin of the East Sea (east coast of Korea), using DNA barcoding. The eggs of P. herzensteini and G. stelleri were relatively widely distributed along the east coast of Korea, whereas those of P. stellatus and K. bicoloratus were narrowly distributed; in particular, the eggs of P. stellatus were restricted to areas near bays. The eggs, which share common morphological characteristics (such as a homogeneous yolk and smooth membrane) were divided into three groups according to egg size: group A (more than 1.60 mm in egg diameter, including genera Hippoglossoides and Microstomus), group B (1.00–1.60 mm, including genera Kareius, Glyptocephalus, and Platichthys), and group C (less than 1.00 mm, including genera Limanda and Pseudopleuronectes). This paper provides an overview of the morphological characteristics of the eggs of the family Pleuronectidae collected from the east coast of Korea. Our approach to the analysis of eggs, based on DNA barcoding, morphological characteristics, and geographic distributions, provides a rapid and accurate basis for identifying spawning areas and spawning periods, thus facilitating the assessment and management of fisheries stocks and resources.

Ultrastructural Studies of Germ Cell Development and the Functions of Leydig Cells and Sertoli Cells associated with Spermatogenesis in Kareius bicoloratus (Teleostei, Pleuronectiformes, Pleuronectidae).

The ultrastructures of germ cells and the functions of Leydig cells and Sertoli cells during spermatogenesis inmale Kareius bicoloratus (Pleuronectidae) were investigated by electron microscope observation. Each of the well-developed Leydig cells during active maturation division and before spermiation contained an ovoid vesicular nucleus, a number of smooth endoplasmic reticula, well-developed tubular or vesicular mitochondrial cristae, and several lipid droplets in the cytoplasm. It is assumed that Leydig cells are typical steroidogenic cells showing cytological characteristics associated with male steroidogenesis. No cyclic structural changes in the Leydig cells were observed through the year. However, although no clear evidence of steroidogenesis or of any transfer of nutrients from the Sertoli cells to spermatogenic cells was observed, cyclic structural changes in the Sertoli cells were observed over the year. During the period of undischarged germ cell degeneration after spermiation, the Sertoli cells evidenced a lysosomal system associated with phagocytic function in the seminiferous lobules. In this study, the Sertoli cells function in phagocytosis and the resorption of products originating from degenerating spermatids and spermatozoa after spermiation. The spermatozoon lacks an acrosome, as have been shown in all teleost fish spermatozoa. The flagellum or sperm tail of this species evidences the typical 9+2 array of microtubules.

울진바다목장에서 자망으로 어획된 수산자원의 종조성과 계절변동

Variations in the species composition, biomass and size distribution of fisheries resources in the Uljin marine ranching area were investigated using trammel nets at two stations (artificial reef and natural rocky area) from 2009 to 2010. During the survey, a total of 74 species were sampled with a mean density of 132 ind./net and mean biomass of 21.56 kg/net. In the natural rocky area, a total of 45 species were sampled at a mean density of 202 ind./net and mean biomass of 28.81 kg/net, while in the artificial reef area, samples included a total of 56 species, with means of 62 ind./net and 14.30 kg/net. The dominant species, comprising over 3% of the total number of individuals, were Suberites ficus (30.8%), Ovalipes punctatus (19.2%), Paralichthys olivaceus (11.7%), Pleuronectes herzensteini (4.7%), Kareius bicoloratus (3.5%), Pseudopleuronectes yokohamae (3.5%) and Eopsetta grigorjewi (3.0%). The dominant species, in terms of biomass, comprising over 5% of the total biomass, were P. olivaceus (22.1%), S. ficus (18.7%), O. punctatus (7.2%), Hexagrammos otakii (6.6%), P. yokohamae (5.7%), K. bicoloratus and P. herzensteini (5.3%). A cluster analysis and non-metric multidimensional scaling (nMDS) analysis based on the Bray-Curtis similarity of fourth root transformed data for number of species and individuals, was divided into two groups: the artificial reef area (group A) and the natural rocky area (group B).

Complete mitochondrial genome of the Pseudopleuronectes yokohamae (Pleuronectiforll: Pleuronectidae)

In this study, the complete mitochondrial genome of the Pseudopleuronectes yokohamae was sequenced. The mitochondrial genome is 17 383 bp in length, consisting of 13 protein-coding genes, 2 ribosomal RNA genes (rRNAs), 22 transfer RNA genes (tRNAs) and a control region (D-loop). The gene order and composition of P. yokohamae mitochondrial genome was similar to that of most other vertebrates. Two rRNA genes for 12S rRNA (949 bases) and 16S rRNA (1716 bases) are located between tRNA-Phe (GAA) and tRNA-Leu (TAA) and separated by the tRNA-Val. The control region of P. yokohamae, is located after tRNA-Pro and found to be 1679 bp. The overall nucleotides base composition of the heavy strand is A (27.55%), T (26.45%), G (28.75%), C (17.26%). With the exception of the NADH dehydrogenase subunit 6 (ND6) and eight tRNA genes, all other mitochondrial genes are encoded on the heavy strand. The 22 tRNA genes could be folded into a typical clover-leaf secondary structure. The phylogenetic trees consistently show that P. yokohama, Kareius bicoloratus and Platichthys stellatus from the same genus clustered into one branch. The complete mitogenome sequence information of P. yokohamae would provide useful data for further studies on population genetics and molecular systematics.

Diel feeding patterns and daily food intake of juvenile stone flounder Platichthys bicoloratus

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 4h 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 4h (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.

Antifreeze Activity in Temperate Fish from the East Sea, Korea

Antifreeze proteins and glycoproteins [AF(G)Ps] constitute a group of proteins that lower the freezing but not the melting points of aqueous solutions, enabling polar and north-temperate fish to survive in ice-laden environments. However, little is known about antifreeze activity in temperate fish; such work would extend our knowledge on the functions and evolution of AF(G)Ps. In the present study, we screened for antifreeze activity in temperate fish caught off the coast of Jumunjin (<TEX>$37.89^{\circ}N$</TEX>), Gangneung, Korea. Thermal hysteresis (TH) and the ability to inhibit ice recrystallization (IR) in blood, liver, and muscle samples from nine fish were examined to assess antifreeze activity. As the East Sea off the coast of Jumunjin is ice-free year round, we thought it most unlikely that the fish would express antifreeze proteins. Surprisingly, the blood of Pleurogrammus azonus and three types of tissue from Gymnocanthus herzensteini, Zoarces gilli and Kareius bicoloratus exhibited measurable TH values together with the ability to trigger characteristic morphological changes in ice crystals. Blood samples from the three species also evidenced ice recrystallization (IR) inhibition. This implies that AF(G)Ps or other antifreeze-like substances are present in temperate fish even under nonfreezing conditions. These results contribute to our understanding of the functions and origins of antifreeze activity in fish.

Collection Record and Feeding Habits of Larval Spotted Halibut and Stone Flounder in Coastal Shallow Waters off Fukushima, the Pacific Coast of Eastern Japan

Collection Record and Feeding Habits of Larval Spotted Halibut and Stone Flounder in Coastal Shallow Waters off Fukushima, the Pacific Coast of Eastern Japan

Locus Number Estimation of MHC Class II B in Stone Flounder and Japanese Flounder

Members of major histocompatibility complex (MHC) family are important in immune systems. Great efforts have been made to reveal their complicated gene structures. But many existing studies focus on partial sequences of MHC genes. In this study, by gene cloning and sequencing, we identified cDNA sequences and DNA sequences of the MHC class II B in two flatfishes, stone flounder (Kareius bicoloratus) and homozygous diploid Japanese flounder (Paralichthys olivaceus). Eleven cDNA sequences were acquired from eight stone flounder individuals, and most of the polymorphic sites distributed in exons 2 and 3. Twenty-eight alleles were identified from the DNA fragments in these eight individuals. It could be deduced from their Bayesian inference phylogenetic tree that at least four loci of MHC class II B exist in stone flounder. The detailed whole-length DNA sequences in one individual were analyzed, revealing that the intron length varied among different loci. Four different cDNA sequences were identified from one homozygous diploid Japanese flounder individual, implying the existence of at least four loci. Comparison of the cDNA sequences to the DNA sequence confirmed that six exons existed in this gene of Japanese flounder, which was a common feature shared by Pleuronectiformes fishes. Our results proved the multi-locus feature of MHC class II B. The sequences we obtained would provide detailed and systematic data for further research.

Early growth and development of reciprocal hybrids of the starry flounder Platichthys stellatus and stone flounder Kareius bicoloratus.

Larval growth and development of hybrid flounder were observed and compared with those of their parent species. The reciprocal hybrids of female starry flounder Platichthys stellatus and male stone flounder Kareius bicoloratus (hybrid Sb) and of female K. bicoloratus and male P. stellatus (hybrid Bs) both survived and grew to juveniles. Development was divided into nine stages (A-I). Many of the hybrids' traits were identical and intermediate to those of their parents. The position of the eye, however, was primarily sinistral in both hybrids (80% in Sb and 76% in Bs), a trait possessed by P. stellatus (80%) in the western Pacific Ocean. The daily growth rates of the larvae were similar. In the parent species, development was more rapid in P. stellatus than in K. bicoloratus whereas rate of development was intermediate in both Sb and Bs hybrids. The size at settlement [standard length (LS ) at stage H (mean ± s.d.)] was 9·82 ± 1·47 mm for the hybrid Sb and 9·99 ± 0·90 mm for the hybrid Bs, while the minimum age at metamorphosis (initial age at stage H) was 29 days after hatching (DAH) in both hybrids. In comparison, LS at settlement in parent species was 6·43 ± 0·25 mm for P. stellatus and 12·87 ± 1·29 mm for K. bicoloratus. Minimum age at metamorphosis for the parents was 23 DAH at stage G in P. stellatus and 34 DAH at stage H in K. bicoloratus. Thus, the timing of settlement of hybrids was different from that of their parent species. These traits may occur with high frequency in a natural habitat.

울진바다목장에서 어획된 가자미목(Pleuronectiformes) 어류의 군집구조 및 공간분포

To elucidate the variation of species composition, biomass and length distribution of flatfishes by the period and region in the Uljin marine ranching area, bottom trawl survey was investigated at the six stations from Feb. 2008 to Dec. 2010. During the survey period, a total 4 families 17 species in the Pleuronectiformes, average 69,158 <TEX>$ind./km^2$</TEX> and 5,625 <TEX>$kg/km^2$</TEX> were identified, in 2008 appeared in 14 species, average 25,798 <TEX>$ind./km^2$</TEX> and 2,333 <TEX>$kg/km^2$</TEX> and in 2009 appeared in 13 species, average 102,360 <TEX>$ind./km^2$</TEX> and 5,634 <TEX>$kg/km^2$</TEX> and in 2010 appeared in 14 species, average 75,704 <TEX>$ind./km^2$</TEX> and 8,632 <TEX>$kg/km^2$</TEX>. The individual dominant species, occupying over 10% of total individuals, was Pleuronectes herzensteini (20,811 ind., 30.0%), Hippoglossoides pinetorum (18,666 ind., 26.9%) and Glyptocephalus stelleri (13,499 ind., 19.4%) also the biomass dominant species, occuping over 10% of total biomass, was P. herzensteini (2,207 kg, 39.3%), Pleuronectes yokohamae (857 kg, 15.3%), H. pinetorum (761 kg, 13.5%), Kareius bicoloratus (677 kg, 12.1%). From the cluster and MDS analysis based on Bray-Curtis similarity matrix of fourth root transformed data of species number and individuals in the Uljin marine ranching area from Feb. 2008 to Dec. 2010 was divided into two different groups of the flatfishes community in 2008 and from Jan. to Apr. in 2009 and 2010 (Group A) and the pleuronectiform community in from May to Dec. in 2009 and 2010 (Group B). From the cluster and MDS analysis using the similarity of demersal organisms community among six stations, the Uljin marine ranching area was divided into two different groups of Group 1 (St. 1 and St. 3) and Group 2 (St. 2, St. 4, St. 5 and St. 6).

Cloning and characterization of major histocompatibility complex class II genes in the stone flounder Kareius bicoloratus (Pleuronectidae)

Major histocompatibility complex (MHC) class II genes play important recognition roles in the immune system in vertebrates. We cloned the MHC class II genes A and B in the stone flounder (Kareius bicoloratus). The full-length cDNA and DNA sequences of both genes were obtained, and their characteristic motifs were analyzed. The DNA sequence of stone flounder MHC class II A consists of four exons, while gene B contains six exons. The extra intron in gene B might be a common feature in most of its Acanthopterygii orthologs. Several conserved motifs were identified by multiple deduced amino acid sequence alignments of the two genes and their orthologs. The peptide sequences of α chain and β chain shared identity of 86.0-30.1% and 69.8-31.3% with their orthologs, respectively. Bayes phylogenetic trees showed that the stone flounder is closely related to the spotted halibut (Verasper variegates), and the half-smooth tongue sole (Cynoglossus semilaevis). Real-time quantitative PCR showed that in the stone flounder, both genes A and B are highly or moderately expressed in several tissues, including the intestine, spleen and gills, and less expressed or undetectable in the liver, kidney, brain, heart, and gonads. These expression patterns differed slightly from those in other teleosts. This might be a unique phenomenon in the stone flounder. This first study of MHC genes in stone flounder could provide reference data for comparative studies.