The genome sequence of the thickback sole, Microchirus variegatus (Donovan, 1808).

We present a genome assembly from an individual female Microchirus variegatus (the thickback sole; Chordata; Actinopteri; Pleuronectiformes; Soleidae). The genome sequence is 724.7 megabases in span. Most of the assembly is scaffolded into 23 chromosomal pseudomolecules. The mitochondrial genome has also been assembled and is 17.42 kilobases in length.

Genome sequencing and analysis of black flounder (Paralichthys orbignyanus) reveals new insights into Pleuronectiformes genomic size and structure.

Black flounder (Paralichthys orbignyanus, Pleuronectiformes) is a commercially significant marine fish with promising aquaculture potential in Argentina. Despite extensive studies on Black flounder aquaculture, its limited genetic information available hampers the crucial role genetics plays in the development of this activity. In this study, we first employed Illumina sequencing technology to sequence the entire genome of Black flounder. Utilizing two independent libraries-one from a female and another from a male-with 150 bp paired-end reads, a mean insert length of 350 bp, and over 35 X-fold coverage, we achieved assemblies resulting in a genome size of ~ 538 Mbp. Analysis of the assemblies revealed that more than 98% of the core genes were present, with more than 78% of them having more than 50% coverage. This indicates a somehow complete and accurate genome at the coding sequence level. This genome contains 25,231 protein-coding genes, 445 tRNAs, 3 rRNAs, and more than 1,500 non-coding RNAs of other types. Black flounder, along with pufferfishes, seahorses, pipefishes, and anabantid fish, displays a smaller genome compared to most other teleost groups. In vertebrates, the number of transposable elements (TEs) is often correlated with genome size. However, it remains unclear whether the sizes of introns and exons also play a role in determining genome size. Hence, to elucidate the potential factors contributing to this reduced genome size, we conducted a comparative genomic analysis between Black flounder and other teleost orders to determine if the small genomic size could be explained by repetitive elements or gene features, including the whole genome genes and introns sizes. We show that the smaller genome size of flounders can be attributed to several factors, including changes in the number of repetitive elements, and decreased gene size, particularly due to lower amount of very large and small introns. Thus, these components appear to be involved in the genome reduction in Black flounder. Despite these insights, the full implications and potential benefits of genome reduction in Black flounder for reproduction and aquaculture remain incompletely understood, necessitating further research.

Integrative taxonomy of Serrasentis gibsoni n. sp. (Acanthocephala: Isthmosacanthidae) from flatfishes in the Gulf of Mexico.

The Isthmosacanthidae acanthocephalan species of the genus Serrasentis are parasites of marine teleosts and an elasmobranch. In this study, Serrasentis gibsoni n. sp. is described from the intestines of four flatfish species (Paralichthyidae), namely Ancyclopsetta quadrocellata, Cyclopsetta chittendeni, Syacium gunteri, and S. papillosum from 10 oceanic sites in the Gulf of Mexico (GoM). Twenty sequences of the 'barcoding' region of cytochrome C oxidase subunit I gene were obtained from 20 adults of Serrasentis gibsoni n. sp. Additionally, five sequences of the barcoding region were obtained from five adults of rhadinorhynchid Gorgorhynchus lepidus from C. chittendeni, S. papillosum and one species of Haemulidae, Haemulom aurolineatum, from five oceanic sites from the GoM. Two phylogenetic approaches were followed: Bayesian inference and maximum likelihood. In both phylogenetic reconstructions, the sequences of Serrasentis gibsoni n. sp. were recovered as a monophyletic group within the genus Serrasentis and placed as a sister group to G. lepidus. However, due to the lack of molecular data for species of the Isthmosacanthidae and Rhadinorhynchidea, these phylogenetic inferences must be taken with caution. Serrasentis gibsoni n. sp. is the first species of Serrasentis described from Paralichthyidae flatfish species from marine waters of the Americas and from the GoM. Based on the barcoding data set analyzed, Serrasentis gibsoni n. sp. appears to have high intraspecific genetic variation; thus, it is necessary to continue exploring the genetic diversity of this species to infer its intraspecific evolutionary patterns.

The genome sequence of the European plaice, Pleuronectes platessa (Linnaeus, 1758).

We present a genome assembly from an individual Pleuronectes platessa(the European plaice; Chordata; Actinopteri; Pleuronectiformes; Pleuronectidae). The genome sequence is 687.4 megabases in span. Most of the assembly is scaffolded into 24 chromosomal pseudomolecules. The mitochondrial genome has also been assembled and is 17.4 kilobases in length.

Peptide mass fingerprinting of preserved collagen in archaeological fish bones for the identification of flatfish in European waters.

Bones of Pleuronectiformes (flatfish) are often not identified to species due to the lack of diagnostic features on bones that allow adequate distinction between taxa. This hinders in-depth understanding of archaeological fish assemblages and particularly flatfish fisheries throughout history. This is especially true for the North Sea region, where several commercially significant species have been exploited for centuries, yet their archaeological remains continue to be understudied. In this research, eight peptide biomarkers for 18 different species of Pleuronectiformes from European waters are described using MALDI-TOF MS and liquid chromatography tandem mass spectrometry data obtained from modern reference specimens. Bone samples (n = 202) from three archaeological sites in the UK and France dating to the medieval period (ca seventh-sixteenth century CE) were analysed using zooarchaeology by mass spectrometry (ZooMS). Of the 201 that produced good quality spectra, 196 were identified as flatfish species, revealing a switch in targeted species through time and indicating that ZooMS offers a more reliable and informative approach for species identification than osteological methods alone. We recommend this approach for future studies of archaeological flatfish remains as the precise species uncovered from a site can tell much about the origin of the fish, where people fished and whether they traded between regions.

The Influence of DNA Extraction Methods on Species Identification Results of Seafood Products.

In terms of species identification, the ultimate aim of extracting DNA is the subsequent amplification of the selected marker; therefore, the quality and quantity of the extracted DNA must be sufficient for PCR-based methods. The purpose of this study is to compare five DNA extraction methods according to the parameters of quantity, quality and simplicity, among others, in order to determine the most suitable method for identification for Cephalopoda, Gadiformes and Pleuronectiformes. The Wizard DNA clean-up system kit (Promega), MPure-12TM automated nucleic acid purification system (MP Biomedicals), Chelex 100 resin (Biorad), DNeasy blood and tissue kit (Qiagen) and a swab method were examined. The obtained DNA quantity was determined by fluorescence, and quality was evaluated with ratios of absorbance of A260/A280 and A260/A230 by agarose gel visualization of the extracts and by analyzing the success of PCR amplifications of 720 bp fragments of cytochrome c oxidase I (COI) for Cephalopods and 465 bp fragments of cytochrome b for Gadiformes and Pleuronectiformes. Statistical results confirmed significant differences between the tested methods according to yield, efficiency and purity and no significant differences with respect to the species employed. The best yields were obtained with the Wizard kit, whereas other methods stand out in terms of their affordability (Chelex) and automation (Mpure).

Integration of Maps Enables a Cytogenomics Analysis of the Complete Karyotype in Solea senegalensis.

The Pleuronectiformes order, which includes several commercially-important species, has undergone extensive chromosome evolution. One of these species is Solea senegalensis, a flatfish with 2n = 42 chromosomes. In this study, a cytogenomics approach and integration with previous maps was applied to characterize the karyotype of the species. Synteny analysis of S. senegalensis was carried out using two flatfish as a reference: Cynoglossus semilaevis and Scophthalmus maximus. Most S. senegalensis chromosomes (or chromosome arms for metacentrics and submetacentrics) showed a one-to-one macrosyntenic pattern with the other two species. In addition, we studied how repetitive sequences could have played a role in the evolution of S. senegalensis bi-armed (3, and 5-9) and acrocentric (11, 12 and 16) chromosomes, which showed the highest rearrangements compared with the reference species. A higher abundance of TEs (Transposable Elements) and other repeated elements was observed adjacent to telomeric regions on chromosomes 3, 7, 9 and 16. However, on chromosome 11, a greater abundance of DNA transposons was detected in interstitial BACs. This chromosome is syntenic with several chromosomes of the other two flatfish species, suggesting rearrangements during its evolution. A similar situation was also found on chromosome 16 (for microsatellites and low complexity sequences), but not for TEs (retroelements and DNA transposons). These differences in the distribution and abundance of repetitive elements in chromosomes that have undergone remodeling processes during the course of evolution also suggest a possible role for simple repeat sequences in rearranged regions.

Successful Spermatogonial Stem Cells Transplantation within Pleuronectiformes: First Breakthrough at inter-family Level in Marine Fish.

As a promising biotechnology, fish germ cell transplantation shows potentials in conservation germplasm resource, propagation of elite species, and generation of transgenic individuals. In this study, we successfully transplanted the Japanese flounder (P. olivaceus), summer flounder (P. dentatus), and turbot (S. maximus) spermatogonia into triploid Japanese flounder larvae, and achieved high transplantation efficiency of 100%, 75-95% and 33-50% by fluorescence tracking and molecular analysis, respectively. Eventually, donor-derived spermatozoa produced offspring by artificial insemination. We only found male and intersex chimeras in inter-family transplantations, while male and female chimeras in both intra-species and intra-genus transplantations. Moreover, the intersex chimeras could mature and produce turbot functional spermatozoa. We firstly realized inter-family transplantation in marine fish species. These results demonstrated successful spermatogonial stem cells transplantation within Pleuronectiformes, suggesting the germ cells migration, incorporation and maturation within order were conserved across a wide range of teleost species.

Chromosome level reference of Atlantic halibut Hippoglossus hippoglossus provides insight into the evolution of sexual determination systems.

Changes in the genetic mechanisms that control sexual determination have occurred independently across the tree of life, and with exceptional frequency in teleost fishes. To investigate the genomic changes underlying the evolution of sexual determination, we sequenced a chromosome-level genome, multitissue transcriptomes, and reduced representation population data for the Atlantic halibut (Hippoglossus hippoglossus), which has an XY/XX sex determination mechanism and has recently diverged (0.9-3.8 Ma) from the Pacific halibut (Hippoglossus stenolepis), which has a ZZ/ZW system. We used frequency and coverage-based population approaches to identify a putative sex-determining factor, GSDF. We characterized regions with elevated heterozygosity and linkage disequilibrium indicating suppression of recombination across a nascent sex chromosome. We detected testis-specific expression of GSDF, the sequence of which is highly conserved across flatfishes. Based on evidence from genome-wide association, coverage, linkage disequilibrium, testis and brain transcriptomes, and sequence conservation with other flatfishes, we propose a mechanism for the recent evolution of an XY sex-determination mechanism in Atlantic halibut. Changes to the ancestral sex-determining gene DMRT1 in regulating the downstream gene GSDF probably coincided with GSDF, or a proximal regulatory element of it, becoming the primary sex-determining factor. Our results suggest changes to a small number of elements can have drastic repercussions for the genomic substrate available to sex-specific evolutionary forces, providing insight into how certain elements repeatedly evolve to control sex across taxa. Our chromosome-level assembly, multitissue transcriptomes, and population genomic data provide a valuable resource and understanding of the evolution of sexual systems in fishes.

Cytogenomics Unveil Possible Transposable Elements Driving Rearrangements in Chromosomes 2 and 4 of Solea senegalensis.

Cytogenomics, the integration of cytogenetic and genomic data, has been used here to reconstruct the evolution of chromosomes 2 and 4 of Solea senegalensis. S. senegalensis is a flat fish with a karyotype comprising 2n = 42 chromosomes: 6 metacentric + 4 submetacentric + 8 subtelocentric + 24 telocentric. The Fluorescence in situ Hybridization with Bacterial Artificial Chromosomes (FISH-BAC) technique was applied to locate BACs in these chromosomes (11 and 10 BACs in chromosomes 2 and 4, respectively) and to generate integrated maps. Synteny analysis, taking eight reference fish species (Cynoglossus semilaevis, Scophthalmus maximus, Sparus aurata, Gasterosteus aculeatus, Xiphophorus maculatus, Oryzias latipes, Danio rerio, and Lepisosteus oculatus) for comparison, showed that the BACs of these two chromosomes of S. senegalensis were mainly distributed in two principal chromosomes in the reference species. Transposable Elements (TE) analysis showed significant differences between the two chromosomes, in terms of number of loci per Mb and coverage, and the class of TE (I or II) present. Analysis of TE divergence in chromosomes 2 and 4 compared to their syntenic regions in four reference fish species (C. semilaevis, S. maximus, O. latipes, and D. rerio) revealed differences in their age of activity compared with those species but less notable differences between the two chromosomes. Differences were also observed in peaks of divergence and coverage of TE families for all reference species even in those close to S. senegalensis, like S. maximus and C. semilaevis. Considered together, chromosomes 2 and 4 have evolved by Robertsonian fusions, pericentric inversions, and other chromosomal rearrangements mediated by TEs.

Double control regions of some flatfish mitogenomes evolve in a concerted manner.

Mitochondrial genomes (mitogenomes) typically contain 13 protein-coding genes, 22 tRNA genes, two rRNA genes, and a single control region (CR). Flatfish mitochondrial genomes (mitogenomes) from three different genera in Bothidae (bothids) contain double CRs that evolved in a concerted manner. How these double CRs maintained identical sequences throughout the evolutionary process is an interesting issue. In the present study, over four hundred arrays of the double CRs of mitogenomes from three bothids (Arnoglossus tenuis, Lophonectes gallus and Psettina iijimae) were performed. Interesting variations between double CRs were observed in P. iijimae mitogenomes, and the networks of CR sequences from P. iijimae indicated a high possibility of genetic information exchange between CRs. No recombination product was detected in our results, indicating that the mechanism of the concerted evolution between the double CRs of P. iijimae was not recombination. We speculate that mismatch repair, a mitochondrial DNA repair mechanism, is a potential explanation for the concerted evolution between these double CRs.

Comparative analysis of the diet composition and its relation to morphological characteristics in Achirus mazatlanus and Syacium ovale (Pleuronectiformes: Osteichthyes) from a Mexican Pacific coastal lagoon

The purpose of this research was to investigate differences in diet composition between Achirus mazatlanus and Syacium ovale, two flatfishes inhabiting in a tropical coastal lagoon and to investigate the relationship of their feeding habits to size, body morphometry and mouths characteristics. Fish were collected during sampling trips conducted regularly from 2011 to 2016 using several types of fishing gear. Total number of analyzed stomachs with some food content was 328 for Achirus mazatlanus from 1.4 to 21.3 cm total length (TL) and 203 for Syacium ovale with 1.3 to 24.0 cm TL. Results indicate that both species share a general diet based on benthic invertebrates and fishes but S. ovale has a more piscivorous habit, which can be explained by a more slender body shape and larger teeth, characteristics which increase prey fish catching performance. Important changes in composition of food categories related to size were not found for any species, but larger fish of both species eat larger ranges of prey sizes, and this ontogenetic change is consistent with recent developments on optimal foraging theory.(AU)

Se investigaron las diferencias en la composición de la dieta entre Achirus mazatlanus y Syacium ovale, dos especies de lenguados que habitan en una laguna costera tropical, y la relación de los hábitos alimentarios con el largo total, la morfometría corporal y las características de las bocas. Los peces fueron colectados regularmente entre 2011 y 2016, mediante varios tipos de artes de pesca diferentes. El número total de estómagos analizados con contenido estomacal fue de 328 para Achirus mazatlanus de 1.4 a 21.3 cm de longitud total (TL) y 203 para Syacium ovale de 1.3 a 24.0 cm TL. Los resultados indican que ambas especies tienen una dieta general basada en invertebrados bentónicos y peces, pero S. ovale tiene un hábito más piscívoro, lo cual puede ser explicado por un cuerpo más alargado y dientes más grandes, características ambas que incrementan el rendimiento de la captura de peces presas. No se encontraron cambios importantes en la composición de las categorías alimentarias relacionados con la talla en ninguna de las especies de lenguados, pero los peces mayores de ambas especies consumen rangos más amplios de tamaños de presas y este cambio ontogénico es consistente con la teoría de forrajeo óptimo.(AU)

Annotated catalogue of type specimens of flatfishes (Osteichthyes: Pleuronectiformes) in the Zoological Institute, St. Petersburg, Russia.

A complete catalogue is provided for the type specimens of flatfishes curated in the ichthyological collection of the Zoological Institute, St. Petersburg. The collection contains a total of 138 type specimens, representing 25 species and one subspecies of eight different flatfish families. The catalogue includes: photographs of type specimens, radiographs of holotypes or largest syntypes, number of specimens, original sampling data (locality, coordinates, depth, collection date and collector), and select morphometric characters for each specimen.

New species and new records of camallanid nematodes (Nematoda, Camallanidae) from marine fishes and sea snakes in New Caledonia.

Recent examinations of camallanid nematodes (Camallanidae) from marine fishes off New Caledonia, collected in the years 2003-2011, revealed the presence of the following five new species of Procamallanus Baylis, 1923, all belonging to the subgenus Spirocamallanus Olsen, 1952: Procamallanus (Spirocamallanus) dispar n. sp. from the common ponyfish Leiognathus equulus (type host) and the striped ponyfish Aurigequula fasciata (both Leiognathidae, Perciformes); Procamallanus (Spirocamallanus) bothi n. sp. from the leopard flounder Bothus pantherinus (Bothidae, Pleuronectiformes); Procamallanus (Spirocamallanus) hexophtalmatis n. sp. from the speckled sandperch Parapercis hexophtalma (Pinguipedidae, Perciformes); Procamallanus (Spirocamallanus) synodi n. sp. from the sand lizardfish Synodus dermatogenys (Synodontidae, Aulopiformes); and Procamallanus (Spirocamallanus) thalassomatis n. sp. from the yellow-brown wrasse Thalassoma lutescens (Labridae, Perciformes). These are described based on light and scanning electron microscopical (SEM) studies. An additional three congeneric nematodes unidentifiable to species are reported from perciform fishes and a shark: Procamallanus (Spirocamallanus) sp. 3 of Moravec et al., 2006, Procamallanus (Spirocamallanus) sp. 1, and Procamallanus (Spirocamallanus) sp. 2. Ten fish species are recorded as new hosts for Camallanus carangis Olsen, 1954. Two camallanids, Procamallanus (Spirocamallanus) sp. 3 (subgravid female) and Camallanus carangis (fourth-stage larva) were also found in the digestive tract of the New Caledonian sea krait Laticauda saintgironsi, serving apparently as postcyclic and paratenic hosts, respectively, for these fish nematodes.

TITLE: Nouvelles espèces et nouveaux signalements de nématodes camallanidés (Nematoda, Camallanidae) provenant de poissons marins et de serpents de mer en Nouvelle-Calédonie. ABSTRACT: L'étude récente de nématodes camallanidés (Camallanidae) de poissons marins capturés au large de la Nouvelle-Calédonie, recueillis de 2003 à 2011, a révélé la présence des cinq nouvelles espèces suivantes de Procamallanus Baylis, 1923, toutes appartenant au sous-genre Spirocamallanus Olsen, 1952 : Procamallanus (Spirocamallanus) dispar n. sp. de Leiognathus equulus (hôte-type) et de Aurigequula fasciata (tous deux Leiognathidae, Perciformes) ; Procamallanus (Spirocamallanus) bothi n. sp. de Bothus pantherinus (Bothidae, Pleuronectiformes) ; Procamallanus (Spirocamallanus) hexophtalmatis n. sp. de Parapercis hexophtalma (Pinguipedidae, Perciformes) ; Procamallanus (Spirocamallanus) synodi n. sp. de Synodus dermatogenys (Synodontidae, Aulopiformes) ; et Procamallanus (Spirocamallanus) thalassomatis n. sp. de Thalassoma lutescens (Labridae, Perciformes). Ces espèces sont décrites sur la base d'études réalisées au microscope électronique à balayage et au microscope photonique. Trois autres nématodes congénères non identifiables au niveau spécifique sont signalés chez des poissons perciformes et un requin : Procamallanus (Spirocamallanus) sp. 3 de Moravec et al., 2006, Procamallanus (Spirocamallanus) sp. 1 et Procamallanus (Spirocamallanus) sp. 2. Dix espèces de poissons sont rapportées comme nouveaux hôtes pour Camallanus carangis Olsen, 1954. Deux camallanidés, Procamallanus (Spirocamallanus) sp. 3 (femelles subgravides) et Camallanus carangis (larve du quatrième stade) ont également été trouvés dans le tube digestif du serpent marin de Nouvelle-Calédonie, Laticauda saintgironsi, qui semble servir respectivement d'hôte post-cyclique et d'hôte paraténique pour ces nématodes de poissons.

Polymorphism and multiple correlated characters: Do flatfish asymmetry morphs also differ in swimming performance and metabolic rate?

Phenotypic polymorphisms often differ in multiple correlated traits including morphology, behavior, and physiology, all of which can affect performance. How selection acts on these suites of traits can be complex and difficult to discern. Starry flounder (Platichthys stellatus) is a pleuronectid flatfish that exhibits rare polymorphism for the direction of eye migration and resulting whole-body asymmetry. P. stellatus asymmetry morphs differ subtly in several anatomical traits, foraging behavior, and stable isotope signatures, suggesting they may be ecologically segregated, yet performance and metabolic differences are unknown.Here we tested the hypothesis that sinistral and dextral P. stellatus asymmetry morphs diverge in performance and routine metabolic rate (RMR) by comparing prolonged swimming endurance (time to exhaustion at a constant swimming speed), fast-start swimming velocity and acceleration, and rate of oxygen consumption. Based on subtle morphological differences in caudal tail size, we expected sinistral P. stellatus to have superior prolonged swimming endurance relative to dextral fish, but inferior fast-start performance.Sinistral P. stellatus exhibited both significantly greater prolonged swimming performance and fast-start swimming performance. However, sinistral P. stellatus also exhibited greater RMR, suggesting that their general swimming performance could be enhanced by an elevated metabolic rate.Divergence between P. stellatus asymmetry morphs in swimming performance and metabolic rates contributes to growing evidence of ecological segregation between them, as well as our understanding of possible ecological consequences of asymmetry direction in flatfishes. These data provide an example of the complexity of polymorphisms associated with multiple correlated traits in a rare case of asymmetry polymorphism in a marine flatfish species.

The complete mitochondrial genome of Cynoglossus interruptus and its novel rearrangement (Pleuronectiformes: Cynoglossidae).

The complete mitochondrial genome was determined for the Cynoglossus interruptus belonging to the family Cynoglossidae. The length of the complete mitochondrial genome is 17,262 bp, consisting of 13 protein-coding genes, 22 tRNA genes, two rRNA genes, and a control region. The gene rearrangement related to tRNAGln and a control region gene were found, forming the gene order of CR-Ile-Gln-Met. Phylogenetic analysis using mitochondrial genomes of 12 species showed that C. interruptus formed a well-supported monophyletic group with other Cynoglossus species.

Gene rearrangements in the mitochondrial genome of robust tonguefish, Cynoglossus robustus (Pleuronectiformes: Cynoglossidae) and a comparative analysis with other Cynoglossus fishes.

The complete mitochondrial genome was determined for the Robust tonguefish Cynoglossus robustus belonging to the family Cynoglossidae. The length of the complete mitochondrial genome is 16,720 bp, consisting of 13 protein-coding genes, 22 tRNA genes, two rRNA genes, and a control region. Rearrangements of the tRNAGln and a control region gene were found and tRNAGln is translocated from the light to the heavy strand. Phylogenetic analysis using mitochondrial genomes of 12 species showed that C. robustus formed a well-supported monophyletic group with other Cynoglossus species.

Evidence for a Robertsonian fusion in Solea senegalensis (Kaup, 1858) revealed by zoo-FISH and comparative genome analysis.

BACKGROUND: Solea senegalensis (Kaup, 1858) is a commercially important flatfish species, belonging to the Pleuronectiformes order. The taxonomy of this group has long been controversial, and the karyotype of the order presents a high degree of variability in diploid number, derived from chromosomal rearrangements such as Robertsonian fusions. Previously it has been proposed that the large metacentric chromosome of S. senegalensis arises from this kind of chromosome rearrangement and that this is a proto-sex chromosome. RESULTS: In this work, the Robertsonian origin of the large metacentric chromosome of S. senegalensis has been tested by the Zoo-FISH technique applied to two species of the Soleidae family (Dicologlossa cuneata and Dagetichthys lusitanica), and by comparative genome analysis with Cynoglossus semilaevis. From the karyotypic analysis we were able to determine a chromosome complement comprising 2n = 50 (FN = 54) in D. cuneata and 2n = 42 (FN = 50) in D. lusitanica. The large metacentric painting probe gave consistent signals in four acrocentric chromosomes of the two Soleidae species; and the genome analysis proved a common origin with four chromosome pairs of C. semilaevis. As a result of the genomic analysis, up to 61 genes were annotated within the thirteen Bacterial Artificial Chromosome clones analysed. CONCLUSIONS: These results confirm that the large metacentric chromosome of S. senegalensis originated from a Robertsonian fusion and provide new data about the chromosome evolution of S. senegalensis in particular, and of Pleuronectiformes in general.

A new species of sinistral flatfish of the genus Chascanopsetta (Teleostei: Bothidae) from off Papua New Guinea, western Pacific Ocean.

Left-eyed flounders of the genus Chascanopsetta Alcock 1894 (Bothidae) occur in the Indian, Pacific, and Atlantic oceans at depths ranging from 120 to 1500 meters. They possess some unique features in bothid fishes including a strongly compressed and elongated body and a tremendously large mouth. Currently, nine species of Chascanopsetta are recognized, and three of them (C. micrognatha Amaoka Yamamoto 1984, C. lugubris Alcock 1894 and C. prognatha Norman 1939) are distributed in the West Pacific. We collected 25 specimens of Chascanopsetta during 11 biodiversity expeditions carried out mainly in the West Pacific. Among them, eight specimens taken off Papua New Guinea present morphological features that differ from those of the three nominal species known in the West Pacific. In this study, we examined these eight specimens of unknown affinity and compared their morphology to that of specimens of other congeneric species. Results of these comparisons showed that these specimens represent an undescribed species of Chascanopsetta, named herein, C. novaeguineae sp. nov.. The new species resembles C. elski Foroshchuk 1991, which is known only from the Saya de Malha Bank in the western Indian Ocean, in having a high number of gill rakers (> 13). However, the combination of the following characters further distinguishes C. novaeguineae sp. nov. from C. elski: longer jaws, narrower interorbital width, and number of pseudobranches (21-25 vs. 26-27). The DNA sequences from the mitochondrial cytochrome oxidase subunit I (COI) gene from C. novaeguineae sp. nov. and other species were obtained and compared to confirm its taxonomic status and to infer its tentative phylogenetic position within the Chascanopsetta.

Duplicated major histocompatibility complex class II genes in the tongue sole (Cynoglossus semilaevis).

The major histocompatibility complex (MHC) molecule plays an important role in the vertebrate immune system. However, we have a limited understanding of the MHC genomic structure in teleosts. Using gene cloning and family analysis, we isolate the MHC class II genes in the tongue sole (Cynoglossus semilaevis) and find that both class II A and class II B genes are duplicated (named Cyse-DAA and Cyse-DBA, Cyse-DAB and Cyse-DBB, respectively). The class II A genes consist of four exons with a highly conserved genomic structure, but each gene has unique and defining exon 2 and intron 2 sequences. The class II B genes have a conserved six-exon genomic structure, with intron 3 splitting the ß2 encoding region into two exons. Each class II B gene has unique variations in exon 2 and intron 1 sequences. The two class II A genes have similar expression patterns among tissues, with high levels in spleen and gill. Both class II B genes have similar patterns, with high expression in spleen, gill and intestine. The alleles of MHC class II have wide distribution and reliable inheritance in the families analysed. This indicates that the duplicated MHC genes are all classical class II genes. The class II gene duplication with divergent exon and intron sequences, but similar expression patterns in tongue sole provides new insights into MHC evolution.