Conger Myriaster Research Articles

Effects of water temperature on white-spotted conger Conger myriaster activity levels determined by accelerometer transmitters

The effect of water temperature on white-spotted conger activity was examined using acoustic accelerometer transmitters to understand thermal effects on the behavior of a target fishery species. We recorded swimming activities of 21 congers using video cameras and compared the body undulation frequency with acceleration values measured using accelerometer transmitters in the body cavity. We found a significant, positive, linear relationship between the acceleration values and activity (body undulation frequency) of congers. We conducted a calibration trial to evaluate the relationships between conger activities and acceleration values measured using accelerometer transmitters, which confirmed the body undulation frequency of congers was associated with its swimming activity. We also examined the effect of water temperature on conger activity levels. The activity levels of eight congers at water temperatures from 10 to 28 °C were tested using accelerometer transmitters. We found a positive relationship between the conger activity levels and water temperatures between 10 and 26 °C, whereas the activity declined between 26 and 28 °C. These results demonstrate that accelerometer transmitters can quantitatively measure changes in the activity of white-spotted conger with water temperature in nature.

Age determination for whitespotted conger Conger myriaster through somatic and otolith morphometrics.

It is difficult to determine ages of eels via otoliths, because multiple alternating translucent and opaque zones in the otoliths are hard to identify. In this study, we developed an efficient age determination method for whitespotted conger (Conger myriaster), using random forest models with otolith weight and length, total body length, capture location and season as predictors. 409 specimens were collected from six locations in Yellow and East China Sea between October 2016 and December 2017. Overall OOB error rate was 17.36% compared with 16.26% for the external cross-validation dataset, and the error of age was within one year. Otolith weight and total length were the most important predictors, followed by otolith length, capture locations and seasons. There were no significant differences between the results derived from otolith/somatic morphometrics and otoliths annuli in the estimation of age composition and von Betalanffy Growth Functions growth curve. Our results demonstrated that random forest model with otolith and somatic morphometrics is an efficient and reliable approach for age determination of C. myriaster, which may also be applied to other eel species.

Review of the congrid eel genus Conger (Anguilliformes: Congridae) in Taiwan.

The congrid eel genus Conger in Taiwan is reviewed. Five species are recognized, including C. jordani, C. cinereus, C. macrocephalus, C. myriaster and a newly collected species, C. philippinus. A mature male specimen of Conger myriaster is described for the first time. Specimens previously identified as C. japonicus (= C. myriaster) were misidentifications of above mentioned species. The diagnostic characters are discussed. Detailed data on all five species and a key to species in Taiwan are provided.

Detection of ascaridoid nematode parasites in the important marine food-fish Conger myriaster (Brevoort) (Anguilliformes: Congridae) from the Zhoushan Fishery, China

BackgroundThe whitespotted conger Conger myriaster (Brevoort) (Anguilliformes: Congridae) is an extremely marketable food fish, commonly consumed as sashimi or sushi in some Asian countries (i.e. Japan, Korea and China). Conger myriaster is also suspected as being an extremely important source of human anisakidosis. However, there is currently very little information on the levels of infection with ascaridoid nematode parasites in this economically important marine fish. The aims of the present study are to determine the species composition, prevalence and mean intensity of ascaridoid parasites of C. myriaster caught in the Zhoushan Fishery.ResultsA total of 1142 third-stage ascaridoid larvae were isolated from 204 C. myriaster. The overall prevalence of infection was 100% (mean intensity 5.6). Nine species of such larvae were accurately identified using integrative taxonomic techniques involving both morphological and genetic data; these included Anisakis pegreffii, A. typica and A. simplex (sensu stricto) × A. pegreffii, Hysterothylacium fabri, H. aduncum, H. sinense, H. amoyense, H. zhoushanense and Raphidascaris lophii. Although high levels of infection and species richness were revealed in C. myriaster, most of the ascaridoid parasites (1135 individuals) were collected from the body cavity and visceral organs of the fish and only seven individuals of A. pegreffii were found in the musculature.ConclusionsThis study represents the first report C. myriaster from the Zhoushan Fishery being heavily infected with third-stage ascaridoid larvae. Among the ascaridoid larvae parasitic in this fish, an important etiological agent of human anisakidosis, A. pegreffii (L3), represents the predominant species. The genus Hysterothylacium has the highest species richness, with H. fabri (L3) being the most prevalent species. This high level of infection of A. pegreffii (L3) in C. myriaster suggests a high risk of anisakidosis or associated allergies for people consuming raw or poorly cooked fish originating from this marine area. These findings provide important basic information on the occurrence and infection parameters of ascaridoid nematodes in this economically important marine fish. They also have significant implications for the prevention and control of human anisakidosis when conger eels from the Zhoushan Fishery are consumed.

Feeding ecology of Conger myriaster and structure of the food webs in artificial reef zone, Laoshan Bay, China

Based on cage net and longline fishing surveys in Laoshan Bay, China, from April 2015 to January 2017, a total of 279 Conger myriaster stomach samples were analyzed to study their feeding ecology, including diet composition, feeding type, feeding grade, feeding intensity, trophic niche, and trophic level. The stomach content analysis of nine key fish species (including Sebastes schlegelii, Hexagrammos otakii, Hexagrammos agrammus, Sebastiscus mamoratus, Lateolabrax maculatus, etc.), were conducted to examine the food webs in artificial reef zone. The results showed that the diet of C. myriaster consisted of more than 30 species belonging to seven orders, in which shrimps were the most dominant prey species, followed by fishes and cephalopods. The dominant species in the diet of C. myriaster were H.otakii, Enedrias fangi, Trachypenaeus curvirostris, Ammodytes personatus and Alpheus japonicas. The diet composition of C. myriaster varied with season and anal length. Fishes and shrimps were the two important groups throughout the years. Cephalopods were predominant in spring. Cephalopods and crabs were predominant in Autumn. Fish eggs were eaten mostly during winter. Fish eggs and T. curvirostris were the dominant prey groups of the C. myriaster with anal length ≤120 mm, whereas A. personatus and A. japonicas were the dominant prey groups of the C. myriaster with anal length 120-130 mm, H.otakii and E.fangi were the dominant prey of the C. myriaster with anal length ＞130 mm. The percentage of empty stomach of C. myriaster varied significantly with season, but the mean stomach fullness index did not. The percentage of empty stomach and mean stomach fullness index did not differ significantly among different anal length groups. The trophic levels of the key fish species were higher than level 3, with C. myriaster at the top of food webs (with a trophic level of 4.636). Decapoda, crabs, amphipoda and molluscs were the main prey of key fish species, while Crustaceans, E. fangi, H. otakii and A. personatus were the main preys of L. maculatus and C. myriaster.

Relationship between the spatiotemporal distribution of Conger myriaster and environmental factors in the southern waters off the Shandong Peninsula during autumn and winter

Relationship between the spatiotemporal distribution of <i>Conger myriaster</i> and environmental factors in the southern waters off the Shandong Peninsula during autumn and winter

Age determination and growth estimates of the white-spotted conger eel, Conger myriaster (Brevoort, 1856) in marine waters of South Korea

The age and growth of conger eel, Conger myriaster, were investigated by measuring transversely sectioned sagittal otoliths samples from 635 individuals. Sample ages ranged from 1 to 13 years in the female data. Parameters of the von Bertalanffy growth function were estimated using nonlinear regression from back-calculation, mean length of samples at age relationships, and otolith weight-at-age relationships. Best-fitting value of the three methods was the otolith weight-at-age relationship (r2 = .87). Parameters of otolith weight-at-age were estimated as L∞ = 143.76 cm, K = 0.081, and t0 = −1.285. Maximum oocyte diameter (MOD) ranged from 50 to 430 μm. Reproductive traits of ovaries showed a positive relationship between GSI and MOD (r2 = .8515). It is suggested that oogenesis begins to develop from 4 years of age and at lengths of about 45 cm TL. In conclusion, these data provide reliable fundamental data for the fish stock management of Conger myriaster in South Korea.

Evaluating the approaches of habitat suitability modelling for whitespotted conger (Conger myriaster)

Habitat suitability models (HSMs) are effective for evaluating habitat suitability and guiding the conservation and exploitation of fishery resources. Using species presence-absence and environmental data collected from a 2011–2015 of bottom trawl survey, we developed and evaluated four habitat suitability models to examine the trends of habitat suitability for a long-distance migration fish, whitespotted conger (Conger myriaster). Generalized additive model (GAM) showed a higher explanatory power than generalized linear model (GLM) and random forest model (RF). Depth and bottom temperature were the most powerful predictors for conger distribution in spring and fall, respectively. We conducted cross-validation study to evaluate the predictability of these models, and random forest model showed consistently better performance than the other models. The spatial distribution of suitable habitat predicted by the best model was mapped in the survey area to inform the exploitation of this species, which showed remarkable annual variations in autumn.

Neoascarophis sinensis n. sp. (Nematoda: Cystidicolidae), a parasite of Conger myriaster (Brevoort) (Anguilliformes: Congridae) in Chinese waters.

Neoascarophis sinensis n. sp. collected from the whitespotted conger Conger myriaster (Brevoort) (Anguilliformes: Congridae) in the Yellow and East China Seas, is described using both light and scanning electron microscopy. The new species is characterised mainly by the body size (8.5-10.5 mm in the males, 9.5-14.0 mm in the females), the location of the vulva (near equatorial region of the body), the non-bifurcate deirids, the lengths of the vestibule (40-50 µm in the males, 30-60 µm in the females) and glandular oesophagus (2.5-3.1 mm in the males, 3.1-3.5 mm in the females) and the morphology and length of the spicules (left spicule 400-410 µm, right spicule 130-150 µm). Neoascarophis sinensis n. sp. is the first species of Neoascarophis Machida, 1976 reported from the anguilliform fish and is also the only species of this genus found in the Chinese waters.

The Identity ofConger japonicus(Anguilliformes: Congridae)

The number of species of the congrid eel genus Conger in Japan has been unsettled for more than half a century. The principal authors have disagreed over how many species are present and what their correct names are. The main question involves the identity of Conger japonicus Bleeker, 1879. It has variously been treated as a valid species or a synonym of Conger myriaster (Brevoort, 1856). We examined the holotype and determined that Conger japonicus is a synonym of Conger myriaster. The four valid species of Conger in Japan are Conger cinereus, Conger myriaster, Conger erebennus, and Conger jordani.

Longline selectivity for white-spotted conger Conger myriaster (Brevoort, 1856) in Haizhou Bay, China

Conger myriaster is one of the most commercially important fish stocks in the Haizhou Bay, China. As the type of longline fishing hook has a significant effect on its capture, three hook sizes (nos. 302, 303, 304) were compared in experiments conducted along the Haizhou Bay from September to November 2012. C. myriaster selectivity analysis using the different hook widths was obtained by analysing the catch rate, CPUE, total length distribution and selection curves. The log-normal model equation was used to explore the longline selection, and anova was employed to analyse the difference in catch rate and CPUE among the three hook sizes. The longline selectivity for C. myriaster was well described by a log-normal model equation. Hook no. 303 proved to have the highest catch rate, CPUE, and the estimated model lengths within three types of hooks tested in the experiments, in accordance with the fact that no. 303 is also the favourite hook used by local fishermen. Overall, the present study indicates that hook no. 303 has the best selection and is an appropriate size for sustainable utilisation of C. myriaster.

Inactivation of Anisakis simplex L3 in the flesh of white spotted conger (Conger myriaster) by high hydrostatic pressure and its effect on quality

ABSTRACTKoreans consume much seafood; the country is surrounded on the east, west and south by the sea. Koreans have eaten raw sashimi for a long time. However, a concern in the raw sea food industry is that the parasitic nematode Anisakis simplex L3 occurs naturally in marine fish. Thus, the fishery industry needs a non-thermal processing method. High hydrostatic pressure (HPP) has been demonstrated to be effective. White spotted conger flesh containing 20 live larvae was exposed to different pressures (150 and 200 MPa for 1 and 5 min; 250 and 300 MPa each for 1 min). The viability of A. simplex L3 was significantly (p < 0.05) reduced in the flesh of white spotted conger by the stepwise increase of high pressure and time. The conditions required to eliminate A. simplex L3 were as follows: 200 MPa for 5 min or 300 MPa for 1 min. The flesh of the white spotted conger treated at 300 MPa for 1 min was whiter and yellower than untreated controls or that treated at 200 MPa for 5 min. No significant changes (p > 0.05) in any of the Hunter colour (‘L’, ‘a’ and ‘b’) values were found after HPP at 200 MPa for 5 min. The fresh treated at 300 MPa for 1 min scored < 4.0 (the defect limit of quality) of flavour, texture and overall acceptability in untrained sensory evaluation using a seven-point hedonic scale. However, the flesh treated at 200 MPa for 5 min scored > 5.0 (‘like’) for all sensory parameters. This study suggested that HPP at 200 MPa for 5 min could potentially be used for the inactivation of A. simplex L3 in raw fishery food products without any concomitant changes in their colour or sensory qualities.

Particular gene order and complete mitochondrial genome of Beach conger (Conger japonicus)

Beach conger (Conger japonicus) is a demersal and carnivorous species belonging to the family Congridae. In the present study, the complete mitochondrial genome of the C. japonicus was first determined. The mitochondrial genome of C. japonicus is 17,778 nucleotides, comprising 13 protein-coding genes, 2 ribosomal RNA genes, 22 tRNA genes, and 2 main non-coding regions (the control region and the origin of the light strand replication), which is consistent with other vertebrates. However, its gene order is different from other vertebrates (except for C. myriaster). The Cytb gene, tRNAThr and the control region are located between the ND5 gene and the ND6 gene in C. japonicus while they are between the ND6 gene and the tRNAPhe gene in other vertebrates. The same gene order also appeared in C. myriaster. The mitochondrial genome of C. japonicus and C. myriaster, which are currently the only two members of Conger genus with complete mitochondrial genome, appeared in the gene rearrangement, so we speculated that the mitochondrial genome of all species from Conger genus may appear in the gene rearrangement. However, to clarify the speculation, more mitochondrial genomes of Conger genus will be needed in the future. In addition, phylogenetic analysis result demonstrated that C. japonicus and C. myriaster clustered in a clade and formed a sister relationship.

Simultaneous Detection and Prevalence of Allergens in Anisakis Species Isolated from Marine Fishes

This study was conducted to develop a multiplex reverse transcription (RT) PCR for the detection of Anisakis allergens and to investigate the relationship between allergen profiles and anisakid larvae isolated from Scomber japonicus, Trichiurus lepturus, and Conger myriaster in Korea. The species of Anisakis was determined using Anisakis pegreffii-specific PCR and restriction fragment length polymorphism analysis. The prevalence and profiles of five Ani s allergens were examined by multiplex RTPCR. A. pegreffii and Anisakis typica accounted for 97.1 and 2.9%, respectively, of the 140 larvae examined. In A. pegreffii, allergen prevalence was 41.2% for Ani s 1, 72.1% for Ani s 2, 69.9% for Ani s 3, 86.7% for Ani s 4, and 93.4% for Ani s 5. Most A. pegreffii larvae had multiple allergen profiles, and 80.7% of A. pegreffii carried both Ani s 4 and Ani s 5, which are heat-resistant allergens. Fifty-two to 65% of A. pegreffii isolated from S. japonicus and C. myriaster carried all five Ani s allergens.

여수 돌산도 연안 낭장망에 부수어획된 어류 종조성

The species composition of bycatch species in the coastal waters of Yeosu were determined by monthly sample collection using a gape net with wings in 2014. Of a total of 32 fishes collected, the dominant species were Ammodytes personatus, Conger myriaster leptocephali, Sebastes inermis, Trichiurus lepturus, Thryssa kammalensis, Leiognathus nuchalis, Syngnathus schlegeli, Thryssa adelae and Hexagrammos otakii. These 9species accounted for 95.2% of the total number of individuals collected. Most of the fish caught were juveniles and small fishes. Based on the results of multidemensional scaling (MDS) analysis, the bycatch fishes were divided into five group.

Population genetic structure of the European conger (Conger conger) in North East Atlantic and West Mediterranean Sea

Assessment of population genetic structure is crucial in species conservation and stock management. The use of multiple markers is recommended to obtain accurate studies. In this study, a panel of five microsatellite loci described for Conger myriaster was optimized for the European conger eel Conger conger. These are the first hypervariable nuclear loci employed for C. conger population study and have a high discrimination power. A total of 67 alleles were observed for Atlantic and Mediterranean samples with an average number of alleles per locus of 13.4 (range 4–24). Variation at these microsatellite loci was combined with mitochondrial control region sequences (395bp) to explore genetic structure of C. conger across the Cantabrian Sea (North East Atlantic ocean) and the West Mediterranean Sea. Overall, there is not total isolation between the Atlantic and the Mediterranean stocks, as previously suggested in other studies, but a subtle differentiation. Cross-species amplification of microsatellite loci in C. conger is hoped to encourage further population studies of this species and the development of new nuclear markers in order to provide scientific advice for the stock management.

Differences and Variations among Anguilla japonica, Muraenesox cinereus and Conger myriaster from the Yellow Sea.

Genomic DNAs were extracted from the muscle of twenty-one specimens of three eel species collected in Anguilla japonica (AJ), Muraenesox cinereus (MC) and Conger myriaster (CM) from the Yellow Sea, respectively. In the present study, 7 oligonucleotides primers generated 191 specific loci in the AJ species, 226 in the (MC) species and 181 in the CM species, respectively. The primer BION-02 generated the most loci (a total of 83), with an average of 11.86 in the AJ species. The specific loci generated by oligonucleotides primers exhibited inter-individual-specific characteristics, thus revealing DNA polymorphisms. With regard to average bandsharing value (BS) results, individuals from Conger myriaster species (0.808) exhibited higher bandsharing values than did individuals from Muraenesox cinereus species (0.729) (p<0.05). The longest genetic distance (0.430) displaying significant molecular difference was also between individual no. 01 within Anguilla japonica eel species and individual no. 04 within Anguilla japonica species. In this study, the dendrogram resulted from reliable seven oligonucleotides primers, indicating three genetic clusters composed of group I (ANGUILLA 01~ANGUILLA 07), group II (MURAENESOX 08~MURAENESOX 14) and group III (CONGER 15~CONGER 21). The existence of species differentiation and DNA polymorphisms among three eel species were detected by PCR analysis. As mentioned above, a dendrogram revealed close relationships between individual identities within three eel species. High levels of a significant genetic distance among three eel species showed this PCR approach is one of the most suitable tools for individuals and/or species biological DNA studies.

Anisakiasis: Report of 15 Gastric Cases Caused by Anisakis Type I Larvae and a Brief Review of Korean Anisakiasis Cases.

The present study was performed to report 15 anisakiasis cases in Korea and to review the Korean cases reported in the literature. Total 32 Anisakis type I larvae were detected in the stomach of 15 patients by the endoscopy. Single worm was detected from 12 cases, and even 9 larvae were found from 2 cases. Epigastric pain was most commonly manifested in almost all cases, and hemoptysis and hematemesis were seen in 1 case each. Symptom manifestations began at 10-12 hr after eating fish in 73.3% cases. Endoscopy was performed 1-2 days after the symptom onset in most cases. The common conger, Conger myriaster, was the probable infection source in 7 cases. In the review of Korean anisakiasis cases, thus far, total 645 cases have been reported in 64 articles. Anisakis type I larva was the most frequently detected (81.3%). The favorable infection site of larvae was the stomach (82.4%). The common conger was the most probable source of human infections (38.6%). Among the total 404 cases which revealed the age and sex of patients, 185 (45.8%) were males, and the remaining 219 (54.2%) were female patients. The age prevalence was the highest in forties (34.7%). The seasonal prevalence was highest in winter (38.8%). By the present study, 15 cases of gastric anisakiasis are added as Korean cases, and some epidemiological characteristics of Korean anisakiasis were clarified.

Combined modeling of fish behavior and fishing operations for conger eel fishery in Ise Bay

In order to simulate the conger eel (Conger myriaster) fishery in Ise Bay, a typical semi-enclosed bay in Japan, we developed a fishery simulator that consists of a fish behavioral model and a fishing operations model. The fish behavioral model considers the migration effect as well as the growth rate of individuals and changes in population size. In the behavioral model with migration, the direction of fish movement is determined by the preference intensities for the environmental factors of water temperature and dissolved oxygen. The change in population size is calculated by using a general population dynamics model considering natural and fishing mortalities. In the first step, the fishing mortality was estimated by the actual fish catch data. Studies have clarified that environmental conditions such as oxygen-deficient water in summer have a large influence on the migration and distribution of C. myriaster. Although the simulated catch per unit effort (CPUE) based on actual fishing operations data was able to describe general features of the annual variability, some improvement of the model will be necessary for more accurate prediction. In the next step, the fish behavioral model was combined with a fishing operations model, which predicts the behavior of trawling boats based on economic conditions and resource distribution. The combined model reproduced the boats’ fishing locations and their fish catch amounts well. The model was applied to evaluate the effects of fishery management and clarified that the control of fine-net use is an effective means to increase the fishery profit.

Biological characteristics of Conger myriaster during the initial stage of spawning migration in the East China Sea

The biological characteristics of Conger myriaster in the East China Sea were studied in May and June (summer), and in November and December (winter), from 2009 to 2010. C. m yriaster was collected mainly at stations in the survey area contained within longitudes 125°E and 128°E and latitudes 28°N and 33°N. Depths and bottom water temperatures for the positive stations ranged from 73 to 186 m and 12.5 to 19.2 °C in summer, and from 65 to 187 m and 13.8 to 21.4 °C in winter. A total of 107 specimens included 64 pre-vitellogenesis (peri-nucleolus to early oil droplet stages) females, 16 mid-vitellogenesis (primary to secondary yolk globule stages) females, 24 pre-meiosis males (spermatogonial proliferation stage), and three sex-unidentified specimens. The gonads of summer-collected mid-vitellogenesis females were more developed than those of winter-collected mid-vitellogenesis females. Additionally, mid-vitellogenesis females were collected mostly where bottom water temperature was lower than 20 °C in both summer and winter. On the other hand, males were captured only in winter and were all pre-meiosis individuals. This suggested that C. m yriaster has different behaviors between females and males. Furthermore, sex ratios (female:male) were 46:0 in summer and 34:24 in winter. The presence of mid-vitellogenesis females and the absence of males in summer suggested different spawning migration routes and/or seasons for females and males.