Molecular diet analysis of Anguilliformes leptocephalus larvae collected in the western North Pacific.

Natural diets of leptocephalus larvae have been enigmatic. In this study, we collected DNA samples from the gut contents and body surface of leptocephali belonging to the five Anguilliform families (Anguillidae, Chlopsidae, Congridae, Muraenidae, and Serrivomeridae) from the northwest Pacific and performed next-generation 18S rDNA sequencing. Wide variety of eukaryotes was detected in both samples, from which eight eukaryotic groups (jellyfish, conoid parasite, tunicate, copepod, krill, segmented worm, fungi, and dinoflagellate) were selected on the basis of abundance. All groups except conoid parasites were common in both the samples. Cnidarian 18S rDNA reads were the most abundant in both the samples; however, the number of samples having cnidarian reads and the read counts were significantly higher in the body surface scraping samples than in the gut content samples, regardless of careful rinsing of the body surface. These results indicate that the cnidarian DNAs are most likely found because of cross contamination from the body surface and/or environment. 18S rDNA read counts of copepod and tunicate in the gut contents were greater than or comparable with those in the body surface scraping samples, which may correspond to the previous observations of fecal pellets and larvacean houses in the leptocephali gut. Thus, the present study supports previous implications that leptocephali utilize detritus materials, so called marine snow.

Estrogen suppresses bcl2 expression through dnmt1 in Japanese eel ovarian follicle.

Japanese eels are commercially valuable species in Asian aquaculture. This study evaluated whether salmon pituitary extract (SPE) or 17ß-estradiol (E2) treatment can induce cytotoxic activity in eel ovarian follicles. Follicular cells died after exposure SPE for 24-h culture in an in vitro culture. Moreover, the E2 treatment also significantly reduced follicular cell counts. These results reveal that the inhibition of follicular cell numbers by SPE may occur through SPE-induced steroidogenesis. Results of a quantitative PCR analysis indicated that adding E2 to the culture decreased bcl2 and increased dnmt1 mRNA expression in Japanese eel follicular cells after 24 h. The results of a promoter assay revealed that E2 significantly increase dnmt1 promoter activity through estrogen receptor-binding site. An in silico analysis predicted several putative transcription factors targeting the bcl2 gene promoter region. Methylation of the bcl2 promoter accounted for the downregulation of bcl2 by E2-mediated dnmt1. The DNA methylation level of the bcl2 gene was significantly higher in E2-treated follicular cells than that in the control group. Finally, the E2-induced hypermethylation pattern of the bcl2 promoter and the reduction in follicular cell numbers were suppressed by adding an MTase inhibitor. Our findings demonstrate that estrogen has a negative effect on the reproductive system of female eels by regulating an epigenetic mechanism during artificial maturation.

Transcriptomic analysis of the differentiating ovary of the protogynous ricefield eel Monopterus albus.

BACKGROUND: The ricefield eel is a protogynous hermaphroditic Synbranchiform species that changes sex naturally from female to male, which offers an interesting model for studying gonadal (particularly ovarian) differentiation in vertebrates. In the present study, transcriptome sequencing of the gonad of ricefield eel larvae was performed to explore the molecular mechanisms underlying the ovarian differentiation and development. RESULTS: A total of 301,267,988 clean reads were generated from cDNA libraries of gonadal tissues of ricefield eel larvae at 6, 9, 12, and 20 days post hatching (dph), which contained undifferentiated gonads, differentiating ovaries, ovaries with oogonia, and ovaries with meiotic oocytes, respectively. De-novo assembly of all the clean reads generated a total of 265,896 unigenes with a mean size of 720 bp and a N50 of 1107 bp. RT-qPCR analysis of the developmental expression of 13 gonadal development-related functional genes indicated that RNA-seq data are reliable. Transcriptome data suggest that high expression of female development-related genes and low expression of male development-related genes in the early gonads of ricefield eel larvae participate in the cascade of sex differentiation leading to the final female phenotype. The contrasting expression patterns of genes involved in retinoid acid (RA) synthesis and degradation might result in peak production of RA at 12 dph in the gonad of ricefield eel larvae, and induce molecular events responsible for the initiation of meiosis before the meiotic signs could be observed at 20 dph. In addition, only stra6 but not stra8 could be identified in gonadal transcriptome data of ricefield eel larvae, and the expression pattern of stra6 paralleled those of genes involved in RA synthesis, suggesting that stra6 may be a downstream target of RA and play a role in RA metabolism and/or meiotic initiation in the gonad of ricefield eel larvae. CONCLUSIONS: The present study depicted the first large-scale RNA sequencing of the gonad of ricefield eel larvae, and identified many important functional genes, GO terms and KEGG pathways involved in gonadal development and germ cell meiosis. Results of the present study will facilitate future study on the ovarian differentiation of ricefield eels and other teleosts as well.

Nuclear and membrane progestin receptors in the European eel: Characterization and expression in vivo through spermatogenesis.

Characterization of all the progestin receptor genes (PRs) found in the European eel has been performed. There were five membrane PRs (mPRs): mPRα (alpha), mPRAL1 (alpha-like1), mPRAL2 (alpha-like2), mPRγ (gamma), mPRδ (delta) and two nuclear PRs (nPRs or PGRs): pgr1 and pgr2. In silico studies showed that the C and E(F) domains of Pgr are well conserved among vertebrates whereas the A/B domain is not. Phylogeny and synteny analyses suggest that eel duplicated pgr (pgr1 and pgr2) originated from the teleost-specific third whole genome duplication (3R). mPR phylogeny placed three eel mPRs together with the mPRα clade, being termed mPRα, mPRAL1 and mPRAL2, while the other two eel mPRs clustered with mPRγ and mPRδ clades, respectively. The in vivo study showed differential expression patterns along the brain-pituitary-gonad axis. An increase in nPR transcripts was observed in brain (in pgr1) and pituitary (in pgr1 and pgr2) through the spermatogenesis, from the spermatogonia B/spermatocyte stage to the spermiation stage. In the testis, mPRγ, mPRδ and pgr2 transcripts showed the highest levels in testis with A spermatogonia as dominant germ cell, while the highest mPRα, mPRAL1 and mPRAL2 transcripts were observed in testis from spermiating males, where the dominant germ cell were spermatozoa. Further studies should elucidate the role of both nuclear and membrane progestin receptors on eel spermatogenesis.

Opportunistic spawning of tropical anguillid eels Anguilla bicolor bicolor and A. bengalensis bengalensis.

Information on the spawning migration, spawning ecology and life history of tropical eels in the Indo-Pacific region is very limited. The physiological and morphological characteristics of tropical freshwater eels, Anguilla bicolor bicolor and A. bengalensis bengalensis collected in Malaysia were examined in relation to their downstream migration patterns. A total of 455 eels were collected over monthly intervals between February 2014 and January 2016 and we examined both gonadosomatic index and gonad histology features. In both species, close positive relationships between advanced maturation stages and eye, fin, gonadosomatic indexes were found in males and females. A. bengalensis bengalensis was found to be larger and heavier than A. bicolor bicolor at the time of seaward migration. The final stage of maturation for seaward spawning migration occurred throughout the year in A. bicolor bicolor, although that of A. bengalensis bengalensis was estimated to six months due to the limited number of samples. These results suggest that year-round spawning in the open ocean occurs in the tropical eel. This non-seasonal spawning ecology is notably different from that of temperate eels, which are known to follow a well-defined spawning season, with spawning migrations generally taking place during autumn months.

Silvering and swimming effects on aerobic metabolism and reactive oxygen species in the European eel.

Silvering, the last metamorphosis in the eel life cycle induces morphological and physiological modifications in yellow eels (sedentary stage). It pre-adapts them to cope with the extreme conditions they will encounter during their 6000-km spawning migration. A previous study showed that silver eels are able to cope with reactive oxygen species (ROS) over-production linked to an increase in aerobic metabolism during sustained swimming, but the question remains as to whether this mechanism is associated with silvering. A sustained swimming session decreased red muscle in vitro mitochondrial oxygen consumption (MO2) but increased ROS production in both eel stages. The swimming exercise used here was perhaps too intense to induce a stimulation of mitochondrial function or biogenesis even when antioxidant enzyme activities were unchanged. Pro-oxidant/antioxidant imbalance by lipid peroxidation increased in yellow but significantly decreased in silver eels. The silvering process therefore appears to allow a pre-adaptation of red muscle radical metabolism to the demands of spawning migration.

A new species of Apterichtus (Anguilliformes: Ophichthidae) from the Marquesas Islands.

A new finless ophichthid eel, Apterichtus succinus sp. nov., is described based on a single specimen collected from the Marquesas Islands. The new species closely resembles A. klazingai Weber, 1913 in the shape and coloration of its head and its total vertebral count. The former differs from the latter in having more preopercular pores (4 vs. 3), fewer preanal vertebrae (54 vs. 56-63), a single tooth on the prevomer (generally absent), a shorter head (14.8 in TL vs. 12-14 in TL), and larger spots on its head and nape. Three species of Apterichtus (A. succinus, A. klazingai, and Apterichtus mysi McCosker & Hibino, 2015) are recognized from the Marquesas Islands.

Three new species of the genus Chlopsis (Anguilliformes: Chlopsidae) from the Indo-Pacific.

Three new species of false moray eels belonging to the genus Chlopsis, family Chlopsidae, are described and illustrated. Chlopsis sagmacollaris, from Western Australia, is characterized by its distinct color pattern with a unique dark saddle on the nape and paler body pigmentation than all other congeners. Chlopsis nanhaiensis, from Taiwan, has a bicolored body with its dorsal-fin origin behind a vertical through posterior margin of gill opening. These characters are shared with C. apterus, C. bicolor, C. bidentatus and C. orientalis sp. nov., but C. nanhaiensis has fewer total vertebrae than other bicolored species (ca. 120 in C. nanhaiensis vs. 125-140 in other four species). Chlopsis orientalis, from Vietnam, is distinguished from all other congeners except C. bicolor by its simple bicolored body, head length (ca. 10% of total length), position of dorsal-fin origin (distinctly behind a vertical through posterior margin of gill opening), and counts of preanal and total vertebrae (35 and 135). Although C. orientalis resembles C. bicolor in meristics and morphometrics, it differs in its pigmentation and possession of stouter intermuscular bones. These new species represent the first records of the genus Chlopsis from the northwestern Pacific Ocean and the eastern Indian Ocean.

A new genus and species of worm eels, Sympenchelys taiwanensis (Anguilliformes: Ophichthidae: Myrophinae), from the northwestern Pacific Ocean.

A new genus and species of ophichthid eel, Sympenchelys taiwanensis is described. The genus is distinguishable from all other myrophine genera by having neural and haemal spines with well-developed paddle-like tips, and from two closely similar genera, Mureaenichthys Bleeker 1853 and Skythrenchelys Castle & McCosker 1999, by the following combination of characters: an unconstricted gill opening; a minute flap just posterior to the gill opening; a slender cleithrum; three preopercular pores; a slender and distinctly tapered maxilla; an undeveloped supraoccipital crest; and large and recurved teeth on jaws and vomer. Sympenchelys taiwanensis is described from five specimens collected from Taiwan, the northwestern Pacific Ocean.

A new species of moray eel (Anguilliformes: Muraenidae) from Taiwan, with comments on related elongate unpatterned species.

The following nine elongate unpatterned muraenid species of the subfamily Muraeninae, including one new species, are recognized from Taiwan and adjacent waters: Gymnothorax albimarginatus (Temminck & Schlegel), G. dorsalis Seale, G. melanosomatus Loh, Shao & Chen, G. phasmatodes (Smith), G. prolatus Sasaki & Amaoka, G. sagmacephalus Böhlke, Pseudechidna brummeri (Bleeker), Strophidon sathete (Hamilton) and G. pseudomelanosomatus new species, described from two specimens. This new moray eel is distinguished from its similar species, G. melanosomatus, by the following features: grey brown body (vs. black), snout length 20.5% (vs. 17.8%) of head length, smaller eye diameter 8.2% (vs. 10.0%) of head length; preanal length 49.5% (vs. 58.5%) total length, and preanal vertebrae 89-89 (vs. 105-109). Phylogenetic relationships of the nine species were examined using nucleotide sequence data from partial sequences of mitochondrial ND5 gene (600 bp), and seven species form COI (600 bp). The genetic analyses suggest that G. pseudomelanosomatus is distinct from G. melanosomatus and the other six species of Gymnothorax. Morphological features and mitogenetic affinities strongly suggest that "G." dorsalis should be placed in Strophidon rather than in Gymnothorax. The results also suggest that employment of ND5 and COI gene sequences are rather useful for identification of species and for obtaining reasonable insights into the phylogeny of the muraenid species.

A new species of the worm-eel genus Neenchelys (Anguilliformes: Ophichthidae) from southern Taiwan.

A new ophichthid worm-eel, Neenchelys gracilis sp. nov., is described from a specimen collected from southwestern Taiwan. It differs from its congeners by having: a minute pectoral fin, many filamentous cirri on the anterior nostril rim; a very slender body; a very small gill opening; and a vertebral formula of 30-78-200.

Renaming of three recently described eels of the genus Neenchelys (Teleostei: Anguilliformes: Ophichthidae) from the western Pacific.

In our earlier paper (Ho et al., 2013), we described three new species of the eel genus Neenchelys Bamber, 1915. Unfortunately, the critical step of registering the work in ZooBank was omitted, thus rendering the names unavailable. In this paper, we present abbreviated descriptions of the new species in order to make these names available in accordance with the amended Article 8.5 of the International Code of Zoological Nomenclature.

A new species of Neenchelys (Anguilliformes: Ophichthidae: Myrophinae) from the eastern Indian Ocean.

A new worm eel, Neenchelys andamanensis, is described based on a single specimen collected from a depth of 520-531 m, Andaman Sea, eastern Indian Ocean. The new species is similar to N. daedalus, N. nudiceps, and N. similis in its total vertebral count and slender body, however, it differs from the latter three in having a shorter tail (60% TL vs. 70-76%), more numerous preanal vertebrae (77 vs. 59-71), and shorter pectoral fins (2.4% HL vs. 21-27%). Although the new species resembles N. mccoskeri in some proportional characters, the former species is distinguishable from the latter by its higher total vertebral count (221 vs. 172-184), position of the dorsal-fin origin (horizontal distance from the origin to a vertical through mid-anus 65% of trunk length vs. 46-59%) and width of the interorbital region (4.5% of head length vs. 8.2-16%). A revised key to the species of Neenchelys is provided.

A new species of Muraenichthys (Anguilliformes: Ophichthidae) from the Indo-Pacific, with revised generic diagnosis.

A new worm eel (Ophichthidae, Myrophinae), Muraenichthys velinasalis, is described based on five specimens (97.9-281.0 mm of total length) collected from Taiwan, Philippines, northeastern Australia, Vanuatu, and Sri Lanka. Muranichthys velinasalis is most similar to M. philippinensis and M. schultzei in the position of the dorsal-fin origin behind a vertical through mid-anus, but can be easily distinguished from the latter two species by the condition of the posterior nostril, unique character of M. velinasalis within Muraenichthys, and by the shape of the teeth on the innermost row of the upper jaw (relatively robust and slightly pointed vs. slender and pointed), arrangement of upper-jaw teeth (irregularly biserial anteriorly and uniserial posteriorly vs. completely uniserial in M. philippinensis, biserial or triserial in M. schultzei), and its more numerous or fewer preanal and total vertebrae (44-51 vs. 59-60 in M. philippinensis, 42-47 in M. schultzei; 136-139 vs. 128-130 in M. philippinensis, 119-128 in M. schultzei). The genus Muraenichthys is re-defined based on all currently valid species by the following combination of characters: eyes located anterior to mid-jaw; inner hole of posterior nostril above upper lip, and outer hole usually outside of mouth, with a prominent but short projected flap anteriorly; a single pore between anterior and posterior nostrils; three preopercular pores; teeth on jaws, vomer, and intermaxillary area; tooth shape variable, blunt to pointed but not distinctly recurved and tooth length equal or less than a half of eye diameter; teeth on jaws and vomer arranged in one to five rows; gill opening constricted, its height<170% of eye diameter; pectoral fins absent.

Review of the arrowtooth eel genera Dysomma and Dysommina in Taiwan, with the description of a new species (Anguilliformes: Synaphobranchidae: Ilyophinae).

Species of the synaphobranchid eel genera Dysomma and Dysommina from Taiwan are reviewed. A total of eight species in Dysomma and one species in Dysommina are recognized. A new Dysomma species is described based on four specimens collected from off Taiwan. It differs from its Taiwanese congeners in having 137-139 total vertebrae, pectoral fin well-developed, 2 intermaxillary teeth, 4 compound teeth on vomer, 40-48 total lateral-line pores, the last at about middle of body, and a uniform brownish color. A key to all species in these two genera in Taiwan is provided.

New species of the snake eels Echelus and Ophichthus (Anguilliformes: Ophichthidae) from Taiwan.

Three new species of ophichthid eels, subfamily Ophichthinae, are described and illustrated from specimens collected at fish markets in Taiwan. Included are: Echelus polyspondylus sp. nov., which is unique in its vertebral number (172-183), dorsal-fin origin (behind gill openings), and coloration (anal-fin membrane black posteriorly); Ophichthus bicolor sp. nov., which is unique in its mean vertebral formula (18-64-158), dorsal-fin origin (well behind gill openings), dentition (teeth large and conical), and contrasting coloration (tan dorsally, white ventrally); and O. shaoi sp. nov., which is unique in its mean vertebral formula (11-69-159), and prominent lip barbels. A key to Taiwanese species of Echelus and Ophichthus is provided.

The eels of the genus Nettenchelys, with description of a new species from Taiwan (Teleostei: Anguilliformes: Nettastomatidae).

The species of the genus Nettenchelys are summarized. Nine species are recognized on the basis of adult specimens: Nettenchelys dionisi Brito, N. erroriensis Karmovskaya, N. exoria Böhlke & Smith, N. gephyra Castle & Smith, N. inion Smith & Böhlke, N. paxtoni Karmovskaya, N. proxima new species, N. pygmaea Smith & Böhlke, and N. taylori Alcock. Another species, N. bellottii (D'Ancona) is based on a larva. Nettenchelys gephyra is redescribed on the basis of additional specimens from northeastern Taiwan, Indonesia and Australia. Nettenchelys proxima new species is described from a specimen from southwestern Taiwan. Nettenchelys sp. reported by Uyeno & Sasaki (1983) is found to be a specimen of Facciolella. Information on larvae is updated based on new knowledge of the genus.

Notes on the congrid eel genus Parabathymyrus from the western Pacific Ocean, with the description of a new species (Pisces: Anguilliformes: Congridae).

The congrid eel genus Parabathymyrus from the western Pacific Ocean is reviewed and three species are recognized: Parabathymyrus macrophthalmus from Japan, Taiwan, Vietnam and Australia, P. brachyrhynchus from Taiwan, Vietnam, the Philippines, Vanuatu and Solomon Islands, and a new species, P. philippinensis sp. nov., is described based on two specimens collected from the Philippines. These three species can be distinguished from each other by the number of total vertebrae (128-137 in P. macrophthalmus, 162-173 in P. brachyrhynchus and 140-141 in P. philippinensis sp. nov.), preanal vertebrae (39-46, 49-58, and 42), preanal lateral-line pores (36-44, 46-54, and 40-42), total lateral-line pores (121-131, 159-169, and 140-141) and supraorbital pores (4, 4 and 3).

Saurenchelys gigas sp. nov., a new nettastomatid eel (Teleostei, Anguilliformes, Nettastomatidae) from the western central Pacific.

Some large Saurenchelys specimens collected from Daxi, Yilan, NE Taiwan, and Da Nang, Vietnam, by bottom trawl at depths of 100-200 m, are described as Saurenchelys gigas new species. They differ from all known adult Saurenchelys species by predorsal length 40.9-46.8, head length 36.8-39.3in % of preanal length, 38-40 preanal vertebrae, 63-70 precaudal vertebrae, 38-42 preanal lateral-line pores, 56-63 preanal dorsal fin rays, and larger size (the maximum size 1155 mm TL).

A new species of Short Brown Unpatterned Moray Eel of the Genus Gymnothorax (Anguilliformes: Muraenidae) from the Bay of Bengal.

A new species of short brown unpatterned moray eel of the genus Gymnothorax, Gymnothorax mishrai sp. nov. is described from a specimen of 324 mm total length, collected from the Bay of Bengal. The species is distinguished by having the dorsal-fin origin before gill opening, jaw pores with brown rim, two branchial pores, total vertebrae 134 (MVF: 9-59-134), three median intermaxillary teeth, uniserial maxillary and vomerine teeth. The new species is distinctly different from the other eight described species of this group. This species is also the first species of short brown unpatterned moray eel to be reported from India.