Odontobutis Obscura Research Articles

How Japanese eels escape from the stomach of a predatory fish

Predation shapes diversity in the defensive tactics of prey. One specialized defensive tactic is to escape the digestive system of the predator after capture1,2,3,4,5,6,7,8. While most of these defensive tactics involve passive ejection alive from predators' mouths and vents1,2,3,4,5, active escape from the digestive tracts of predators has recently been observed in certain invertebrate species6,7 and fish8. However, no study has yet uncovered the behavioral patterns and escape routes of the prey within a predator's digestive tract. Here, we report the sequential escape processes of the Japanese eel Anguilla japonica from capture to escape via the gills of predatory fish Odontobutis obscura using an X-ray video system. All captured eels had at least one portion of their bodies swallowed into the stomach of the predator. Surprisingly, after being swallowed, most individuals attempted to escape by going back up the digestive tract towards the esophagus and gill, and some of them succeeded in escaping via the predator's gill. Some eels, whose entire bodies were completely inside the stomach, exhibited circling behavior along the stomach, seemingly searching for possible escape routes. An electro-anesthetization experiment revealed that eels utilize various escape routes through gill clefts, rather than just one.

Peek-A-Boo test: a simple test for assessing the effect of anxiolytics on fish behavior.

The potential of pharmaceuticals and personal-care products to alter the behavior of aquatic organisms is a growing concern. To assess the actual effect of these substances on aquatic organisms, a simple but effective behavioral test is required. In this study, we devised a simple behavioral test (peek-a-boo test) to assess the effect of anxiolytics on the behavior of a model fish (medaka, Oryzias latipes). In the peek-a-boo test, we investigated the response of medaka to an image of a predator fish (donko fish, Odontobutis obscura). The test revealed that the time taken for test medaka exposed to diazepam (0.8, 4, 20, or 100 µg/L) to approach the image was shorter by a factor of 0.22-0.65 and the time spent in the area close to the image was longer by a factor of 1.8-2.7 than in the solvent control group for all diazepam exposure groups (P < 0.05). Hence, we confirmed that the peek-a-boo test could detect changes in medaka behavior caused by diazepam with high sensitivity. The peek-a-boo test devised in this study is a simple behavioral test with high sensitivity for fish behavioral alteration.

Functional Characterization of Dark Sleeper (Odontobutis obscura) TBK1 on IFN Regulation.

In East Asia, the dark sleeper, Odontobutis obscura (O. obscura) is a crucial commercial species of freshwater fish; however, its molecular biology research is still undeveloped, including its innate immune system, which is pivotal to antiviral responses. In this study, we cloned and identified the characterization and kinase function of dark sleeper TANK-binding kinase 1 (TBK1), supplementing the evidence of the conservation of this classical factor in fish. First, the ORF of Odontobutis obscurus (O. obscura) TBK1 (OdTBK1) was cloned from liver tissue by RACE-PCR. Subsequent nucleic acid and amino acid sequence analysis suggested that OdTBK1 is homologous with other fish TBK1, and the N-terminal Serine/Threonine protein kinases catalytic domain (S_TKc) and C-terminal coiled coil domain (CCD) are conserved. Subsequently, the cellular distribution demonstrated that OdTBK1 was located in the cytoplasm region. With regard to the identification of functions, OdTBK1 activated several interferon (IFN) promoters' activity and induced downstream IFN-stimulated genes (ISGs) expression. In a canonical manner, wild-type OdTBK1 significantly phosphorylated interferon regulatory factor 3 (IRF3) but failed when the N-terminal region was truncated. Furthermore, overexpression of OdTBK1 decreased viral proliferation remarkably. Collectively, these data systematically analyzed the characterization and function of OdTBK1, initiating the study of the innate antiviral response of dark sleeper.

Functional characterization of dark sleeper (Odontobutis obscura) IRF3 in IFN regulation

The dark sleeper, Odontobutis obscura (O. obscura), is a commercially important species of freshwater sleeper native to East Asia. However, its molecular biology system is unexplored, including the interferon (IFN) signaling pathway, which is crucial to the antiviral response. In this study, we characterised the IFN regulation pattern of dark sleeper interferon regulatory factor 3 (OdIRF3), supplementing evidence of the conservation of this classical pathway in fish. First, the open reading frame (ORF) of OdIRF3 was cloned from the liver tissue by Rapid amplification of cDNA ends (RACE). Amino acid sequence analysis suggested that OdIRF3 is homologous with other fish IRF3 and that the N-terminal DNA-binding domain (DBD) and the C-terminal IRF-association domain (IAD) are conserved. Then, the cellular distribution demonstrated that OdIRF3 is located in the cytoplasm region and transfers into the nuclear region under stimulation. For the function identification, OdIRF3 activated several types of IFN promoters and induced downstream interferon stimulated genes (ISGs) expression. Finally, the overexpression of OdIRF3 significantly decreased viral proliferation. Taken together, these data systematically characterised the sequence, cellular location, and function in IFN expression of OdIRF3, shedding light on the molecular biology mechanism of the dark sleeper.

Threshold Responses in the Taxonomic and Functional Structure of Fish Assemblages to Land Use and Water Quality: A Case Study from the Taizi River

Biological functional traits help to understand specific stressors that are ignored in taxonomic data analysis. A combination of biological functional traits and taxonomic data is helpful in determining specific stressors which are of significance for fish conservation and river basin management. In the current study, the Taizi River was used as a case study to understand the relationships between the taxonomic and functional structure of fish and land use and water quality, in addition to determining the thresholds of these stressors. The results showed that taxonomic structure was significantly affected by the proportion of urban land and specific conductivity levels, while functional metrics were influenced by the proportions of farmland and forest. Threshold indicator taxa analysis found that Phoxinus lagowskii, Barbatula barbatula nuda, Odontobutis obscura, and Cobitis granoei had negative threshold responses along the gradients of urban developments and specific conductivity. There was a significant change in fish taxonomic composition when the proportion of urban land exceeded a threshold of 2.6–3.1%, or specific conductivity exceeded a threshold of 369.5–484.5 μS/cm. Three functional features—habitat preference, tolerance to disturbances, and spawning traits—showed threshold responses to the proportion of farmland and forest. The abundance of sensitive species should be monitored as part of watershed management, as sensitive species exhibit an earlier and stronger response to stressors than other functional metrics. Sensitive species had a positive threshold response to the proportion of forest at 80.1%. These species exhibited a negative threshold response to the proportion of farmland at 13.3%. The results of the current study suggest that the taxonomic and functional structure of fish assemblages are affected by land use and water quality. These parameters should be integrated into routine monitoring for fish conservation and river basin management in the Taizi River. In addition, corresponding measures for improving river habitat and water quality should be implemented according to the thresholds of these parameters.

The Phylogenetic Position of the Cestode Nippotaenia mogurndae Yamaguti et Miyata, 1940 (Cestoda: Nippotaeniidae), a Parasite of the Chinese Sleeper Perccottus glenii Dybowski, 1877 (Actinopterygii: Odontobutidae), Based on a Partial Sequence of the 18S rRNA Gene

A partial sequence of the 18S rRNA gene (1979 bp) of the cestode Nippotaenia mogurndae Yamaguti et Miyata, 1940, a parasite of the Chinese sleeper Perccottus glenii Dybowski, 1877, is obtained. The maximum likelihood (ML) and Bayesian Inference (BI) algorithms are used for phylogenetic analysis that included the sequence and data obtained from GenBank. Both algorithms reveal a close phylogenetic relationship of our N. mogurndae and the N. mogurndae s. str. from its type host, Odontobutis obscura (Temminck et Schlegel, 1845), from Japan. The genetic divergence between these helminths (0.005) corresponds to the level of intraspecies differences typical for groups of cestodes phylogenetically close to the nippotaeniids: Mesocestoididae and Hymenolepididae. The results of the phylogenetic analysis also do not support the separation of nippotaeniid cestodes into two genera: Amurotaenia Achmerow, 1941 and Nippotaenia Yamaguti, 1939.

The phylogenetic placement of Odontobutis obscura base on complete mitochondrial DNA sequence

In our research, 16 sets of primers were used to amplify contiguous, overlapping segments of the complete mitochondrial DNA (mtDNA) of Odontobutis obscura. The aim of our research was to provide some important genetic background information for conservational practice of these valuable fish species. The total length of the mitochondrial genome is 16 864 bp and deposited in the GenBank with accession numbers KT438552. The gene arrangement and transcriptional direction were similar to other bony fishes which contained 37 genes (13 protein-coding genes, 2 ribosomal RNA, and 22 transfer RNAs) and a major non-coding control region. The nucleotide skewness for the coding strands of O. obscura (GC-skew = −0.26) is biased toward G and the negative GC-skew ranges from −0.51(ND2) to −0.24(CO1). The phylogenetic analysis showed that the Gobiiformes could be divided into three groups, Eleotridae, Odontobutidae and Rhyacichthyidae. The O. Obscura and O. Potamophila are sister species and clustered together.

Development of polymorphic microsatellite loci in Odontobutis obscura using Illumina paired-end sequencing and the test of cross-species amplification.

Odontobutis obscura is a bottom-dwelling freshwater fish native to East Asia. Its range encompasses southwest China, western Japan, and Geoje Island in South Korea. Despite its widespread range in China and Japan, only a small and spatially isolated population is found in South Korea. We developed a total of 23 novel and polymorphic microsatellite loci of O. obscura using Illumina paired-end shotgun sequencing and characterized them using 80 Japanese and Korean samples. An extensive genetic polymorphism was detected at these 23 loci, with the observed number of alleles at a locus ranging from 2 to 15 and expected and observed heterozygosities ranging from 0 to 0.656 and 0 to 0.547, respectively. Korean O. obscura exhibited a much lower level of genetic variability than the Japanese population did, probably as a result of long-term isolation combined with historical bottlenecks. The Japanese and Korean populations showed a high level of genetic differentiation with FST = 0.700 and RST = 0.913. Many of our primer sets were successfully transferable to congeneric O. interrupta and O. platycephala, which exhibited even greater polymorphism than Korean O. obscura. In conclusion, our study showed that these 23 microsatellite markers are useful for understanding the conservation biology and population genetic structure of O. obscura and other congeneric species.

Rediscovery of a Fish Acanthocephalan, Acanthocephalus minor (Echinorhynchida: Echinorhynchidae), in the Lake Biwa Basin, Central Japan, with a Review of the Fish Acanthocephalan Fauna of the Basin

Specimens of the echinorhynchid acanthocephalan Acanthocephalus minor Yamaguti, 1935 were collected from the rectum of a dark sleeper, Odontobutis obscura (Temminck and Schlegel, 1845), in an irrigation canal near Lake Biwa, Shiga Prefecture, west-central Japan. This represents a rediscovery of A. minor in the Lake Biwa basin after a gap of nearly 80 years. It appears not to be distributed in Lake Biwa proper, but to occur rarely in rivers and irrigation canals of a limited coastal area around the lake. To date, 10 nominal species of acanthocephalan in four families and three orders have been reported from fish in the Lake Biwa basin. Among these, striking morphological similarities between Acanthocephalus aculeatus Van Cleave, 1931 and its congener A. opsariichthydis Yamaguti, 1935 are noted. It is furthermore suggested that A. gotoi Van Cleave, 1925 could not maintain its population after the basin's wild population of its major host, Anguilla japonica Temminck and Schlegel, 1846, disappeared in the mid-1960s.

Two novel myxosporean species (Myxosporea: Bivalvulida), Myxobolus marumotoi n. sp. and Cardimyxobolus japonensis n. sp., from the dark sleeper, Odontobutis obscura, in Japan

Two new myxosporean species, Myxobolus marumotoi n. sp. and Cardimyxobolus japonensis n. sp. (Myxozoa: Myxosporea: Bivalvulida), are described from the dark sleeper, Odontobutis obscura, in Japan, based on their morphological and molecular characterizations. Plasmodia of M. marumotoi n. sp. (Myxobolidae) grew in the myofiber of trunk muscles, forming pseudocysts. The rounded spore was relatively large, measuring 13.3-15.0 μm (average 13.8) in length, 14.2-15.0 μm (14.6) in width, and 10.0-11.7 μm (10.8) in thickness, with two subspherical polar capsules of 7.9-9.6 μm (8.4) in length by 5.4-6.3 μm (5.9) in width (n = 15). The polar capsules were directed toward the apex of the spore, packing five to six spirals of the polar filament. Plasmodia of C. japonensis n. sp. (Ortholineidae) were surrounded by thin fibrous tissue, forming cysts in the lamina propria of the alimentary tract. The spore was ovoid, wider than long, in valvular view and spindle-shaped in sutural view. It measured 8.8-10.4 μm (9.4) in length, 11.3-12.5 μm (11.9) in width, and 5.2-6.7 μm (5.8) in thickness, with two ovoid polar capsules of 4.2-5.0 μm (4.7) in length by 2.9-3.8 μm (3.3) in width (n = 15). The shell valves of spores often showed a flattened anterior border and semicircular posterior border, and the two polar capsules were directed toward opposite lateral sides. In addition, the sporoplasm contained an iodinophilous vacuole. Almost complete small-subunit (SSU) rDNA sequences, except for primer flanking regions, were obtained for both species; 1,996 bp long for the former and 1,588 bp long for the latter. On phylogenetic trees based on the SSU rDNA sequences of representative species of Bivalvulida, M. marumotoi n. sp. and C. japonensis n. sp. formed a distinct branch in the Henneguya/Myxobolus clade or near but outside this clade, respectively. This study is the first report of the genetic characterization for the genus Cardimyxobolus.

Diversity in interspecific interactions between a nest-associating species, Pungtungia herzi, and multiple host species

Nest association in fishes affects the reproductive success of the host to varying degrees, from complete failure of the host’s reproduction to fitness advantages. Such varying impacts of nest association are considered to result from both the associate’s behavior and the characteristics of the host’s reproduction. To investigate the relationship between the impact of nest associate and host/associate ecology as well as evolutionary strategies involving nest association, we compared reproductive strategies and success between an associate East Asian minnow, Pungtungia herzi, and two host fishes (a goby, Odontobutis obscura, and a catfish, Pseudobagrus nudiceps) that have different reproductive ecologies. The associate frequently spawned around the days on which both hosts spawned, and gained a fitness advantage through continuous egg protection. Spawning by the associate had a negative effect on the survival of O. obscura eggs. Male O. obscura tended to abandon their nest when it was parasitized during the pre-spawning period. This is likely a tactic to alleviate the costs of brood parasitism. In contrast, survival of P. nudiceps eggs was consistently high in all nests, regardless of the intensity of associate’s spawning, and P. nudiceps young fed on cyprinid offspring (most probably the associate’s eggs/young) in the nest. Both P. nudiceps and P. herzi populations likely gain fitness benefits from their relationship. When comparing these two hosts with another known host, the freshwater perch Coreoperca kawamebari, the observed differences in the impact of nest association to the associate species likely correspond to differences in the spatial reproductive resources used by the respective hosts.

Description and innervation of the lateral line system in two gobioids, Odontobutis obscura and Pterogobius elapoides (Teleostei: Perciformes)

Components of the lateral line system and their innervation were studied in Odontobutis obscura (Odontobutidae) and Pterogobius elapoides (Gobiidae), which are benthic and pelagic species, respectively. Innervation of the superficial neuromasts constituting the trunk lateral line system by way of three continuous longitudinal series (dorsal, middle, and ventral series: ld, lm, and lv series, respectively) became apparent for the first time. Innervation patterns indicated that the ld and lv series represented a mixture of displaced rows (from lm series) and new additional rows. In O. obscura, the ld and lv series were poorly developed, whereas both series were well developed in the pelagic P. elapoides, possibly as an adaptation to receive stimuli from above and below. Two extremely elongated nerve branches derived from the lateral ramus of the posterior lateral line nerve innervated the ld and lv series, respectively, in P. elapoides. Homologies of the neuromast rows on the head and body were discussed on the basis of their innervation patterns.

Mitochondrial DNA phylogeny of Japanese freshwater goby, Odontobutis obscura, and an evidence for artificial transplantation to Kanto District

Mitochondrial DNA phylogeny of Japanese freshwater goby, Odontobutis obscura, and an evidence for artificial transplantation to Kanto District

Distribution pattern of two genetically different groups of Odontobutis obscura in the Takatsu River and its vicinity.

Distribution pattern of two genetically different groups of Odontobutis obscura in the Takatsu River and its vicinity.

Flexibility of reproductive tactics and their consequences in the brood parasitic fish Pungtungia herzi (Teleostei: Cyprinidae)

Although previous studies have claimed that Pungtungia herzi (Cyprinidae) is an obligate brood parasite, in this study a significant proportion of P. herzi egg masses was found in crevices formed by stones and rocks, which was not guarded by hosts. Egg masses were also found in almost all nests of a goby Odontobutis obscura, suggesting that P. herzi has two alternative reproductive tactics: brood parasitic spawning and non-parasitic crevice spawning, the latter of which may occur when a shortage of reproductive resources (i.e. host nests) exists. The hatching rates of parasitic egg masses were significantly higher than those of non-parasitic egg masses, and the hatching rate of P. herzi eggs exhibited a strong positive correlation with continuous egg guarding by a reproductive O. obscura male. These results indicate that brood parasitism effectively improves reproductive success in P. herzi. The alternative reproductive tactic of this species suggests that brood parasitism has evolved directly from crevice spawning via the sharing of spawning habitat with host species.

Genetic identification of larvae and juveniles reveals the difference in the spawning site among Cyprininae fish species/subspecies in Lake Biwa

To understand the differences in the spawning sites among Cyprininae fishes in Lake Biwa, we conducted periodic sampling of larvae and juveniles at three sites (irrigation ditch, St. 1; river, St. 2; and satellite lake, St. 3). On the basis of species/subspecies identification by using RAPD analysis, we examined the species composition of the larvae and juveniles at these three sampling sites. The number of specimens was 616, 68, and 117 at St. 1, St. 2, and St. 3, respectively. Based on morphological and genetic identification, the specimens were found to include nine fish species/subspecies, namely, Carassius auratus grandoculis, Carassius cuvieri, Carassius auratus langsdorfii, Cyprinus carpio, Sarcocheilichthys sp., Silurus asotus, Oryzias latipes, Odontobutis obscura obscura, and Rhinogobius sp. The species composition at the three sites also differed. Among the Cyprininae fishes, C. auratus grandoculis, C. auratus langsdorfii, and Cyprinus carpio were found in abundance at St. 1; C. cuvieri was not collected from St. 1 but was found at the other two sites, particularly St. 3. Among the other fishes, Rhinogobius sp. was collected at St. 1 and St. 3, whereas the other four occurred only at St. 1. These results suggest that the selection of spawning sites by C. cuvieri differs to a certain extent from that of the other Cyprininae fishes, and the irrigation ditch in the lake is an important habitat for the larvae and juveniles of native fish species.

Redescription of Trypanosoma ophiocephali Chen 1964 (Kinetoplastida: Trypanosomatina: Trypanosomatidae) and first record from the blood of dark sleeper (Odontobutis obscura Temminck and Schlegel) in China

During the parasite fauna investigation within 2004 and 2005, the freshwater fish trypanosomes were isolated from the blood of dark sleeper (Odontobutis obscura Temminck and Schlegel) and snakehead fish (Ophiocephalus argus Cantor) from Niushan Lake, Hubei Province, China. Blood trypomastigotes were used for light microscopy investigations. The detailed descriptions of three morphological groups of the genus Trypanosoma: Trypanosoma sp. I and Trypanosoma sp. II found in blood of O. obscura, and Trypanosoma sp. III found in blood of O. argus were provided. Morphological features and host species show Trypanosoma sp. III belong to Trypanosoma ophiocephali Chen 1964, an incompletely described species. Infection with trypanosomes of O. obscura was recorded for the first time. According to the size and appearance, the trypanosomes in O. obscura were also tentatively identified as T. ophiocephali Chen 1964.

Genetic Relationships between Japanese and Korean Odontobutis obscura (Pisces, Odontobutidae)

Genetic Relationships between Japanese and Korean Odontobutis obscura (Pisces, Odontobutidae)

淡水魚腸内寄生虫に対する重金属毒性検出の試み

The effects of copper and zinc ions on intestinal parasites in freshwater fish Odontobutis obscura were investigated in the laboratory. The survival of the cestode Amurotaenia mogurndae, and the survival and reproduction of the trematode Asymphylodora macrostoma in CuSO4 and ZnCl2 solutions were tested for five days. The copper levels of the CuSO4 solutions were at 0.00 (control), 0.02 and 0.05 mg·l-1, and the zinc levels of ZnCl2 solutions 0.01 (control), 2.83, 3.19 and 3.38 mg·l-1. No significant differences were detected in the survivals of both parasites and the reproduction of Am. mogurndae between the control and the CuSO4 and ZnCl2 solutions. The concentrations of copper and zinc in water from O. obscura's original habitat and in its muscle tissue measured using ICP-AES showed that the metals did not accumulate in the muscle tissue during the experiment, and that zinc was actually excreted.

Life cycle of Coitocoecum plagiorchis (Trematoda: Digenea: Opecoelidae)

The life cycle of Coitocoecum plagiorchis Ozaki, 1926 ( Coitocaecum is an incorrect subsequent spelling) was studied in the field and laboratory. The study was conducted at the Futatsu River and the Chikugo River, Kyushu, Japan. Adults of C. plagiorchis were obtained from fishes Coreoperca kawamebari, Rhinogobius spp . and Odontobutis obscura. Cotylomicrocercous cercariae with a two-point stylet (= Cercaria distyloides Faust, 1924) were detected in pleurocerid snails ( Semisulcospira spp.). Metacercariae with a cyclocoel were obtained from shrimp ( Neocaridina denticulata). The cercariae were experimentally exposed to the shrimp, and subsequently metacercariae with a cyclocoel were recovered from the shrimp within 24 days after exposure. These metacercariae were identified as C. plagiorchis. The sporocysts, cercariae, metacercariae and adults are briefly described.