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Conger myriaster has a high price on the international market and occupies an important position in aquatic product export in China, and it is widely distributed in the Yellow Sea, the Bohai Sea, the East China Sea, the coastal waters of Japan from southern Hokkaido to northern Okinawa, and the sea near the Korean Peninsula. The experimental aquaculture techniques of C. myriaster include pond culture, industrialized open-flowing water culture, and industrialized recirculating aquaculture. No report has been published on the morphological characteristics or the effects of various morphological traits on the body weight and net body weight of C. myriaster in an industrialized open-flowing water culture. In this study, C. myriaster was collected under this industrialized culture mode and assessed using traditional measurement methods, statistical analysis, and other means to systematically measure and analyze morphological traits. A total of 90 C. myriaster were collected equally from three aquaculture companies along the coast of the Yellow Sea. The body weight (BW), net body weight (NW), total length (TL), body length (BL), body height (BH), soma width (SW), head length (HL), head height (HH), head width (HW), proboscis length (PL), proboscis width (PW), eye diameter (ED), vertical eye diameter (VED), and distance between eyes (DE) were measured individually using an electronic balance, a ruler, and a Vernier caliper. We analyzed the relationships between morphological traits and constructed a truss network diagram of morphological traits. The effects of the morphological traits on BW and NW were studied by correlation analysis, path analysis, multiple regression analysis, and curve fitting. The correlation analysis showed that the correlations of BW with TL, BL, BH, SW, HH, and HW were extremely significant (P < 0.01), with correlation coefficient values of 0.818, 0.829, 0.611, 0.697, 0.667, and 0.642, respectively. The correlations of NW with TL, BL, BH, SW, HH, HW, and VED were extremely significant (P < 0.01), with correlation coefficients of 0.848, 0.857, 0.574, 0.591, 0.617, 0.564, and 0.519, respectively. Path analysis revealed that the path coefficients between BW and three morphological traits (namely BL, BH, and SW) were larger than those for other morphological traits, at 0.631, 0.204, and 0.374, respectively. The path coefficients between NW and these three morphological traits (BL, BH, and SW) were larger than those for other morphological traits, at 0.703, 0.213, and 0.239, respectively. Through determination coefficient analysis, it was observed that the determination coefficient for BL to BW was the largest, with a value of 0.398. The combination of SW and BL had the largest determination coefficient for BW, with a value of 0.162. This indicated that BL was a core morphological trait to determine the BW, and the SW was an important morphological trait to determine the BW. The determination coefficient of BL to NW was the largest at 0.494. The combination of SW and TL had the largest coefficient of determination for NW, with a value of 0.116. This showed that the BL was the core morphological trait to determine the NW, and SW was an important morphological trait to determine the NW. A stepwise regression method was used to establish a regression equation in which the three morphological traits were independent variables and the BW or NW was the dependent variable. The multiple regression equation of the important morphological traits for BW was BW = –642.699 + 1.086 × BL + 3.874 × BH + 7.917 × SW (P < 0.01). The multiple regression equation of the important morphological traits for NW was NW = -526.995 + 1.033 × BL + 3.438 × BH + 4.317 × SW (P < 0.01). Further curve fitting was performed for each morphological trait with BW and NW in the equation. The best fitting models of BL, BH, and SW for BW were the logarithmic function, logarithmic function, and power function, respectively, and the model equations were BW = -3, 542.357 + 608.061lnBL (R2 = 0.929), BW = 14.313BH0.941 (R2 = 0.908), and BW = -1, 028.49 + 416.452lnSW (R2 = 0.920), respectively. The best-fitting models of BL, BH, and SW for NW were the logarithmic, linear, and logarithmic functions, respectively. The model equations were NW = -2, 983.881 + 516.411lnBL (R2 = 0.930), NW = -22.252 + 11.392BH (R2 = 0.914), and NW = -774.583 + 329.017lnSW (R2 = 0.921), respectively. In summary, BL was the core morphological trait affecting the BW and NW of C. myriaster in an industrialized culture model. BH and SW were important morphological traits affecting the BW and NW of C. myriaster in the industrialized culture model. These results provide a theoretical basis for the future identification of germplasm characteristics, genetic breeding, and healthy aquaculture of C. myriaster.

This study investigated the impact of compound probiotics on the growth performance, non-specific immunity, intestinal digestive enzyme, and microbiota of Conger myriaster in a 10-week trial conducted in a recirculating aquaculture system. The control group (CI) was fed diets with added saline, while the test group (PI) was fed diets with compound probiotics (4.2 × 107 CFU/g). The results showed that the growth performance of C. myriaster in the PI group was significantly higher than that in the CI group (P < 0.05). The non-specific immunity and intestinal digestive enzyme activity in the PI group were significantly higher than those in the CI group (P < 0.05). The community richness and diversity of intestinal microbiota in the PI group were significantly higher than those in the CI group (P < 0.05). At the phylum level, the relative abundance of Firmicutes, Bacteroidota, and Actinobacteriota significantly increased (P < 0.05), while the relative abundance of Spirochaetota significantly decreased in the PI group (P < 0.05). At the genus level, the relative abundance of Lactobacillus, Acinetobacter, Bacteroides, Faecalibacterium, Lachnospiraceae_NK4A136_group, and Bifidobacterium was significantly increased (P < 0.05), while the relative abundance of Vibrio and Mycoplasma was significantly decreased in the PI group (P < 0.05). Based on the KEGG functional prediction analysis, the relative abundance of carbohydrate metabolism function in the PI group was significantly higher than in the CI group (P < 0.05). Based on the COG functional prediction analysis, the relative abundance of carbohydrate transport and metabolism function in the PI group was significantly higher than in the CI group (P < 0.05). These results indicate that the dietary supplementation of compound probiotics (4.2 × 107 CFU/g) provided better growth performance, non-specific immunity activity, and intestinal digestive enzyme activity and regulated the homeostasis of intestinal microbiota in C. myriaster. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Dalian Ocean University is the property of Journal of Dalian Ocean University Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The whitespotted conger (Conger myriaster) is an important fish species with high economic value in China and Japan owing to its high nutritional content. It occupies an important position in marine-eel export in China. C. myriaster has the potential to be artificially cultured and has promising economic prospects. Thus, there is growing international interest in C. myriaster research. Indeed, to meet the demands of domestic and foreign markets, artificial culturing of C. myriaster is urgently required. However, at present, there is no report on the research of C. myriaster reared in industrial recirculating aquaculture systems. Feeding frequency has been reported to affect feed intake and growth performance in a number of fish species. Feed management in terms of optimization of feeding frequency has emerged as one of the crucial areas of research in the field of aquaculture. Overfeeding and leftover food disrupts the water quality, while inadequate food supply has direct impact on production cost. Traditional flow through systems uses large volumes of water, and intensified aquaculture has drawbacks, such as large amount of discharged waste from effluent water. Among the excreted nutrients, nitrogen and phosphorus constitute the largest proportion. Sustainability with low environmental impacts is one of the concerns when developing aquaculture systems. Based on the concepts of reduced water consumption and efficient water management, recirculating aquaculture systems offer the possibility of creating a sustainable future for fish production. Thus, a 70-day experiment was conducted to investigate the effects of different feeding frequencies and water quality on the growth performance and physiological and biochemical indices of C. myriaster [body weight: (150.64±5.43) g] reared in industrial recirculating aquaculture systems; physiological and ecological methods were used in this study. The experiment comprised two feeding frequency groups, feeding once (group T1) and twice (group T2) per day, and each treatment group had three replicates. The average body weight of the fish in each culture pond and the water quality indices of the culture system were measured and analyzed every 14 d. At the end of the experiment, the blood, liver, and intestine samples of C. myriaster were collected to determine and analyze growth and physiological indices. The results indicated that (1) the growth performance of group T2 was better than that of group T1. The final body weight, final body length, weight gain, and specific growth rate of group T2 was significantly higher than those of group T1 (P < 0.05). The feed coefficient of group T1 was significantly higher than that of group T2 (P < 0.05). However, no significant differences were found in the final body height, liver body ratio, visceral body ratio, condition factor, or survival rate at different feeding frequencies (P > 0.05). (2) The serum malondialdehyde of group T1 was significantly higher than that of group T2 (P < 0.05). The hepatic alanine aminotransferase and hepatic aspartate transaminase of group T1 was significantly higher than those of group T2 (P < 0.05). The intestinal trypsin of group T2 was significantly higher than that of group T1 (P < 0.05). There were no significant differences in the levels of serum superoxide dismutase, serum catalase, intestinal amylase, or intestinal lipase between groups T1 and T2 (P > 0.05). (3) In the 24 h changes of ammonia nitrogen (NH4+-N) and nitrite nitrogen (NO2–-N), the change patterns of the two indices in outlet of the T1 group were similar to those of the outlet of the bio-filter; the two indices of the outlet water in T1 and T2 groups were one (24:00) and two peaks (20:00 and 08:00) respectively; the difference in NH4+-N in the outlet water of the two test groups within 24 h was significant (P < 0.05); at 04:00 and 08:00, the NO2–-N content of the outlet water of the biofilter was significantly lower than that of the other two test groups (P < 0.05); the 24 h changes range of NH4+-N and NO2–-N in T2 group were smaller than those in T1 group. (4) During the whole test period, each water quality index was maintained within the safe breeding range, and no significant differences were found in NH4+-N, NO2–-N, chemical oxygen demand, and active phosphate concentration between T1 and T2 groups (P > 0.05); at the end of the test, the total nitrogen and total phosphorus of T2 group were significantly higher than those of T1 group (P < 0.05); the biofilter has different treatment effects on various water quality indices, among which the treatment effect on NH4+-N is the most efficient, up to 54.23%. Based on the above results, the feeding frequency of twice per day was better than that of once per day in the industrial recirculating aquaculture mode for C. myriaster (body weight: 150~250 g). Without affecting the survival rate and condition factor, the twice per day group can save costs and improve economic benefits. However, due to the limitations of the test conditions, we did not explore more times of feeding, and further tests are needed in the future. The predominance, which was the high efficiency of water qualities treatment and optimal effect of culture, was demonstrated obviously in closed recirculating aquaculture systems. This study aims to provide a theoretical reference for the appropriate feeding strategy in the industrial recirculating aquaculture model of C. myriaster.

The proximate composition, amino acid, fatty acid and mineral elements of wild and farmed Conger myriaster muscle were compared. Results indicated that the lipid content of farmed fish was significantly higher, while moisture content was significantly lower than that of the wild fish (P<0.05). The contents of all essential amino acids (EAA), half essential amino acids (HEAA) and Tyr, Asp, Glu were significantly higher in farmed Conger myriaster than that in wild fish (P<0.05). The ratios of the WEAA/WTAA (39.92% vs 39.77%) and WEAA/WNEAA (84.29% vs 82.37%) were similar in farmed and wild Conger myriaster (P>0.05). n-3 polyunsaturated fatty acids (PUFAs), n-6 PUFAs and total PUFAs content were lower in wild than that in farmed Conger myriaster (P<0.05). Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) were higher in farmed than wild Conger myriaster (P<0.05). Farmed fish showed significant high content in K and Mg but low in Hg, As and Pb compared to wild fish (P<0.05). In a word, farmed Conger myriaster under investigation have high nutritional qualities and positive health benefits, it is a potentially healthier alternative to the wild Conger myriaster. [ABSTRACT FROM AUTHOR]

In this study, the traditional morphometry method was applied to analyze the standardized measurements together with the meristic counts so as to provide supplementary information for fishery biology, population assessment, and fishery resources protection of C. myriaster. The results of one-way analysis of variance (ANOVA) showed that the greatest divergence was observed between the Dalian and Qingdao populations, whereas the smallest difference was found between the Lianyungang and Zhoushan populations. Statistical difference in tail length (TAL) was detected between all populations. The morphological traits with high C.D values were mostly related to body weight (BW), confirming greater potential variations of these weight-related traits. Principal component analysis (PCA) extracted 7 principal components (PCs) with eigenvalues greater than 1, and the cumulative contribution rate was 72.790%. The results of cluster analysis, together with the PCA and DFA, supported separating the populations into three groups linked with their geographic distribution and their specific environment localization. Considering the particularity of the natural environment of the Bohai Sea and the sophisticated oceanic circulations of the Shandong Peninsula, the relationships of C. myriaster populations in the northwest Pacific Ocean along the China coast were closely related to their geographical distributions and oceanic circulations.

Spawning potential ratio (SPR) is a commonly used biological reference point to inform management decisions; however, the fish reproductivity may vary substantially with different body conditions, and the variability has not been well understood. Here, we examined the maturity, fecundity, and SPR of a marine eel Conger myriaster. The results showed that total fecundity increased with length and hepatosomatic indices (HSI), whereas relative fecundity (total fecundity/body weight) decreased with body weight, suggesting length- and condition-driven reproductive strategies. A length-structured per-recruit model was used to estimate SPR and examine the influence of HSI in resultant management decisions. Our results suggested that this stock was subject to a high risk of recruitment overfishing. Fish condition greatly influences the estimates of SPR-related reference points. For example, when HSI increased from 0.6% to 1.8%, F40% increased by 91%. In addition, using spawning stock biomass to calculate F40% could produce a bias of 23%. We highlight the need for monitoring the changes in fish fecundity and conditions in fisheries assessment, which may contribute to the robust management of data-poor fisheries.

Abstract Background The 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. Results A 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. Conclusions This 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.

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. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: To develop seed production techniques for aquaculture of the common Japanese conger, Conger myriaster, we attempted to induce ovarian maturation and ovulation without exogenous hormone treatment and examined the changes in steroid hormones to understand the endocrine condition of the fish during their maturation process. Juveniles caught in November 2001 (20 to 30cm in total length) were reared for 1.5years in seawater at temperatures ranging from 10 to 20°C before the experiments. Then, 141 randomly selected female eels (58 to 82cm in total length) were maintained at a water temperature of 6°C from April 2003 to March 2004. The initial GSI values (5.0 to 12.0) and oocyte diameters (300 to 400μm) recorded in April 2003 had increased to maximum values of 30.0 and 650μm, respectively, at the end of experiment, in March 2004. In late December 2003, 12 fish with oocytes measuring over 600μm in diameter were selected and divided into an elevated temperature group from 6 to 10°C and a control group of 6°C for 43days. The mean oocyte diameter in the elevated temperature group increased significantly, and one fish (estimated GSI, 47.0) ovulated eggs with an average diameter of 995±46μm on the 41st day at a water temperature of 10°C, in contrast, the control group showed no significant changes in oocyte diameter, and no fish ovulated. Plasma T levels, examined via ELISA, increased with oocyte maturation, with the highest level detected at the migratory nucleus stage, and declined after ovulation. In contrast, plasma E2 was maintained at high levels during the vitellogenic stage, exhibiting the highest value after ovulation. The present study demonstrates that ovarian maturation and ovulation in the common Japanese conger could be achieved through water temperature manipulation. [Copyright &y& Elsevier]

The common Japanese conger Conger myriaster is an important commercial coastal fisheries species in East Asia, but its spawning area has not been determined. A larval sampling survey was conducted in September 2008 along 136°E between 13°N and 22°N, which roughly followed the Kyushu-Palau Ridge in the western North Pacific. Twenty larval specimens were confirmed to be C. myriaster using DNA analysis. Two were newly hatched larvae (preleptocephali) 5.8 and 7.8 mm in total length (TL), which were caught at 17°N. The 5.8 mm TL larva was estimated to be 3-4 days after hatching, the youngest preleptocephalus (i.e., the earliest stage) of this species ever collected. Eighteen other leptocephali were caught at 18°N and 21°N, and these ranged from 18.6 to 40.0 mm TL. Based on these collections, we discerned that there is a spawning area of C. myriaster in the area along the Kyushu-Palau Ridge approximately 380 km south of Okinotorishima Island. Similar to the Japanese eel spawning area along the West Mariana Ridge, the Kyushu-Palau Ridge may play an important role as a landmark of the spawning area. The discovery of this offshore spawning area should lead us to a better understanding of the recruitment mechanisms of C. myriaster, and help to facilitate future international management efforts. [ABSTRACT FROM AUTHOR]

Comparative fishing experiments were carried out in 2010 using tube traps with five hole diameters (8, 15, 18, 20 and 22 mm) to establish the size selectivity of escape holes for white-spotted conger. Selectivity and split parameters of the SELECT model were calculated using the estimated-split and equal-spilt model. From likelihood ratio tests and AIC (Akaike's Information Criterion) values, the estimated-split model was selected as the best-fit model. Size selectivity of escape holes in the tube traps was expressed as a logistic curve, similar to mesh selectivity. The 50% selection length of white-spotted conger in the estimated-split model was 28.26, 33.35, 39.31 and 47.30 cm for escape-hole diameters of 15, 18, 20 and 22 mm, respectively. The optimum escape-hole size is discussed with respect to management of the white-spotted conger fishery. The results indicate that tube traps with escape holes of 18 mm in diameter would benefit this fishery. [ABSTRACT FROM AUTHOR]

Abstract: The anti-predatory performance of hatchery-reared red tilefish (Branchiostegus japonicus) using tube-shaped burrows was studied together with the behavioral characteristics of potential predators, the white spotted conger (Conger myriaster) and the marbled rockfish (Sebastiscus marmoratus). White spotted conger were released in Maizuru Bay (Kyoto, Japan) and tracked using acoustic telemetry; they were also observed in a tank using video recording. White spotted conger tended to remain inside shelters, but occasionally swam outside briefly at night. Attacking behavior of predators and predation avoidance behavior of red tilefish were also recorded in a tank. Red tilefish construct tube-shaped burrows into which they retreat to avoid attack. White spotted conger wandered around the tank, often invading the burrows to prey on red tilefish. Predation by white spotted conger occurred at night. Inside the burrows, red tilefish were not easily caught and were able to escape through the other entrance of the tube-shaped burrow. Marbled rockfish, on the other hand, pounced on red tilefish immediately after prey recognition, ambushing their prey near the burrow entrance. Predation by marbled rockfish was frequently observed around dusk and dawn, but some red tilefish that remained inside burrows survived. White spotted conger is nocturnal and probably an olfactory predator, whilst marbled rockfish is crepuscular and an ambush predator. For stock enhancement of red tilefish, the construction of tube-shaped burrows and their diurnal behavior around the burrows are desirable characteristics in reducing predation by both white spotted conger and marbled rockfish. [Copyright &y& Elsevier]

A subsample of Conger leptocephali collected in the East China Sea (ECS) was genetically analyzed and most were found to be the larvae of Conger myriaster, the most commercially important marine eel species in East Asia. However, these leptocephali (22.3–74.0 mm total length [TL]) did not have a complete row of lateral pigmentation, like the leptocephali of this species are commonly known to have when they are collected over the continental shelf or in coastal waters as they recruit. These leptocephali were in the western edge of the Kuroshio Current and the mixing zone over the shelf in the northern part of the ECS, and two smaller leptocephali (22.3, 46.5 mm TL) were collected to the south of the Ryukyu Islands. This evidence of an ontogenetic change in the presence of lateral pigmentation of C. myriaster indicates that previous efforts to determine the spawning area and recruitment patterns based on only morphological examination of Conger leptocephali in the region must be reconsidered. New research efforts based on genetic identification methods are needed to understand the spawning ecology and recruitment of this important fishery species. [ABSTRACT FROM AUTHOR]

In Tokyo Bay, conger tube-trap fishers voluntarily deployed escape holes of at least 13 mm diameter to reduce the by-catch of young conger smaller than the marketable size of 35 cm total length. Comparative fishing experiments in Tokyo Bay were carried out using tube traps with seven hole diameters (3, 9, 13.5, 14, 15, 17, and 19 mm), to obtain the size-selectivity of the escape-hole size for inshore hagfish Eptatretus burgeri and white-spotted conger Conger myriaster. On the assumption of the geometrical similarity in the combination of body g and hole perimeter m at a given retention probability, a single master curve s( R) = exp(−13.52 + 11.31 R)/(1 + exp [−13.52 + 11.31 R]) was estimated for the two species in terms of relative R = g/ m using the Share Each LEngth's Catch Total (SELECT) process based on a multinomial distribution. Almost all conger and hagfish with a girth equivalent to the hole perimeter were able to pass through the hole. Thus, the two species have a high ability to escape through a narrow space by squeezing the body through the hole in the rigid PVC tube. Optimum escape-hole size is discussed from several objectives for conger tube-trap fishery management, e.g. reduction of hagfish by-catch. This study also specifies the conditions for pooling data when fishing experiments using more than two fishing gears are replicated. [ABSTRACT FROM AUTHOR]

Abstract: The major yolk protein precursor, vitellogenin (VTG) was detected in plasma from vitellogenic females and estradiol-17β (E2)-treated immature females, but not in males and immature females by Western blotting in common Japanese conger Conger myriaster. Its molecular mass was approximately 180 kDa under denaturing and reducing conditions. The common Japanese conger VTG cDNA was cloned from the liver of vitellogenic female. It contains 5110 nucleotides including an open reading frame that encodes 1663 amino acids. The deduced amino acid sequence of the common Japanese conger VTG shares 80% identity with that of eel Anguilla japonica VTG-1, and 45–55%, 32–34% and 27–29% identity with the deduced amino acid sequences of other fish, amphibian and avian VTG with polyserin domain, respectively. In female common Japanese conger, VTG gene was highly expressed in the liver of this species similar with other oviparous vertebrates. The expression levels of VTG gene in the liver increased from the oil droplet stage to the tertiary yolk globule stage and were maintained until the migratory nucleus stage. [Copyright &y& Elsevier]

In this study, we developed a new automatic system, comprised of a radio frequency identification (RFID) system and global positioning system (GPS), for monitoring fishing effort, and effectiveness of effort, in fisheries using many pieces of fishing gear, such as hooks of longlines. The outline of this system is as follows. A single RFID tag with an identification (ID) number is attached to each piece of fishing gear. The RFID tag on the fishing gear passes the antenna of the RFID reader before being shot into the sea and after being hauled up from the sea. Data on the time and geographic location are measured by the GPS and recorded along with the ID number in a personal computer (PC). When a fish is caught, it is brought close to the fish-sorting table. Then, the second antenna of the RFID reader set at the side checks for a catch in the gear. The advantage of this system is that the fishing operation data can be collected without interfering with the fishermen's usual work. The prototype of the system was tested at a conger-eel tube fishery in Tokyo Bay and was able to record data on the time, the location and the catch of individual conger-eel tubes successfully. [ABSTRACT FROM AUTHOR]

Annual changes in the gonadosomatic index (GSI), oocyte diameter, gonadal histology and plasma estradiol-17β (E2) levels were investigated in female common Japanese congerConger myriasterin captivity. Juveniles were caught in September 1999 and reared in seawater at temperatures ranging from 10–20°C for 3 years. All fish were immature when captured in September 1999. GSI and oocyte diameter increased from October 2000, peaked between summer and autumn 2001, and bottomed-out in winter 2001. Plasma E2 level also increased from October 2000, but remained high. The ovarian developmental stage was at the peri-nucleolus stage or the oil droplet stage until September 2000. Vitellogenesis started in October 2000 and oocytes progressed to the tertiary yolk globule stage by summer 2001. However, vitellogenic oocytes regressed in all females after autumn 2001. The neogenetic oocytes began to increase after November 2001 and ovarian development progressed in 2002 as they did in 2001, although maximum GSI in 2002 was half its 2001 value. These data indicate that ovarian development in the common Japanese conger has an annual periodicity, and that these congers may be able to spawn in multiple years under rearing condition. [ABSTRACT FROM AUTHOR]

Estrogen receptor (ER) cDNA was cloned from the liver of common Japanese conger Congermyriaster. Common Japanese conger ER cDNA contains 2543 nucleotides including an open reading frame that encodes 596 amino acids, with a molecular weight of 66.1 kDa. The deduced amino-acid sequence of the common Japanese conger ER shares 85% identity with that of eel Anguilla japonica ER-β, and 39-46% and 53-59% identity with the deduced sequences of ER-α and ER-β of other species, respectively. In a phylogenetic analysis, the common Japanese conger ER was found to cluster with the ER-β of other species. The common Japanese conger ER-β also has six domains (A-F), which are conserved in the nuclear receptor superfamily. The amino-acid sequences in the C and E domains were highly conserved between common Japanese conger ER-β and other ER. However, the other domains showed low homology. In the female common Japanese conger, ER- β mRNA was highly expressed in the liver and pituitary gland. The expression levels of the ER-β gene increased from the oil droplet stage to the primary yolk globule stage and were maintained until the migratory nucleus stage. [ABSTRACT FROM AUTHOR]

To study the population structure of the Japanese conger eel, Conger myriaster, we investigated the age, total length, developmental stage and mitochondrial (mt) DNA genetic variation among the leptocephali collected from three different locations along the east coast of central Japan. A total of 79 individuals was collected at the same period of time in March 1998 from Iwaki (northern site), Odawa Bay (middle site) and Ise Bay (southern site). Results from morphological measurements and otolith age determination indicated that the mean total length of leptocephali from Iwaki was about 10mm shorter than those from Odawa Bay and Ise Bay, the average age of the samples from Ise Bay was about 50 days older than those of the sample from Iwaki and Odawa Bay, and the leptocephali in metamorphic stage appeared only in Ise Bay samples. The otolith data also suggested the existence of at least two spawning seasons in 1997. These regional differences suggested that the early life history characteristics of the Japanese conger eel might differ between geographically different areas along the east coast of central Japan. Phylogenetic analysis based on mtDNA sequence data indicated no significant genetic differentiation between samples collected from different locations, implying intensive gene flow between geographically distant areas. [Copyright &y& Elsevier]

Annual changes in gonadal histology, gonadosomatic index (GSI), and plasma 11-ketotestosterone (11KT) levels were investigated in reared male common Japanese congers, Conger myriaster. Young fish, 20–30 cm in total length and around 20 g in body weight, caught in November 1996 (group 1) and in September 1999 (group 2) were reared for 3 years in seawater at temperatures ranging from 10 to 20 °C.In most fish, only spermatogonia occupied the testes for 1 year and a few months after capture. Spermatocytes appeared in February, and both spermatids and spermatozoa appeared in March, in 1998 for group 1 and in 2001 for group 2. Spermiation was observed from May to September and reduction in testis was observed after October in both groups. GSI and plasma 11KT levels changed with progression of spermatogenesis. Although GSI was less than 1.0 and the plasma 11KT level less than 1.0 ng/ml, in the first year in most fish, both increased in the second year of rearing. GSI peaked in June 1998 (5.3±3.0; mean±standard deviation) in group 1 and May 2001 (2.3±1.3) in group 2, and bottomed in October (0.3±0.1) in both groups. Plasma 11KT levels peaked in March 1998 (5.8±1.9 ng/ml) in group 1 and May 2001 (4.4±2.4 ng/ml) in group 2, and bottomed in August in group 1 and September in group 2 (around 0.1 ng/ml in both groups). Spermatogenesis and changes in GSI and plasma 11KT levels were repeated the following year in both groups.These observations indicate that males have an annual reproductive cycle under rearing conditions. It is possible that wild male common Japanese congers also have multiple spawning seasons in their lives. [Copyright &y& Elsevier]

ABSTRACT: We investigated the process and characteristics of oogenesis in the common Japanese conger Conger myriaster . Young fish caught in November 1996 were reared for use in this experiment. Fish were sampled monthly from December 1997 to August 1998. Some were injected with human chorionic gonadotropin to stimulate ovarian maturation from May to August 1998. Oocytes from the chromatin nucleolus stage to the secondary yolk globule stage were obtained from non-hormone-treated fish; those of more advanced stages were obtained from hormone-treated ones. We divided oocyte development into eight stages from the chromatin nucleolus stage to the maturation stage. The yolk vesicle stage was not separated because yolk vesicles began to appear just after appearance of yolk globules. Oocyte, oil droplet, yolk globule and nucleus diameters all increased concomitant with oocyte development. Oil droplet and yolk globule diameters increased remarkably at the maturation stage. However, zona radiata thickness peaked at the secondary yolk globule stage, decreasing gradually thereafter. Increased gonadosomatic index was related to oocyte development as found in European and Japanese eels receiving hormone treatment to mature. The present study is the first report describing oogenesis characteristics in congrid eels. It indicates that oogenesis is almost identical to that of other anguillid eels. [ABSTRACT FROM AUTHOR]

ABSTRACT: Although essential for fisheries resources management, little is known about the population structure of the Japanese conger Conger myriaster. To search for useful molecular markers for the study of population structures, mitochondrial (mt) and nuclear DNA diversities in the Japanese conger were examined using DNA sequencing and amplified fragment length polymorphism (AFLP) analysis, respectively. A region spanning from part of the 3′ end of the cytochrome b gene to the central part of the control region (~585 base pairs/individual) was sequenced for 73 individuals from five different localities around Japan. A total of 99 variable positions were found, and a total of 67 haplotypes were identified in the 73 individuals. The average sequence differences within samples (1.8–2.4%) was comparable to those between samples (1.9–2.3%). The results of a hierarchical analysis of the sequence data did not suggest clear genetic subdivision among the local samples. Although a total of 499 bands were detected in the AFLP analysis from 58 individuals with three primer sets, no genetic structuring could be suggested. Nonetheless, to elucidate the subtle structure of populations, if any, many more individuals from more localities should be examined in detail. The genetic variations detected in the present study would serve as useful molecular markers for such studies. [ABSTRACT FROM AUTHOR]