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Background: The characteristics and incidence of patients with tricuspid valve (TV) prolapse after leadless pacemaker implantation are unknown. Methods and Results: We retrospectively identified 35 of 85 patients with sufficient echocardiographic TV imaging before and after Micra transcatheter pacing system (Micra TPS) implantation. The post-procedure incidence of TV prolapse was 8.6%, and the cause of prolapse was chordae tendineae rupture. Patients with TV prolapse had significantly longer procedure times and more deployments than patients without TV prolapse. Conclusions: TV prolapse after Micra TPS implantation is not a rare complication and is accompanied by frequent deployments and prolonged procedure times.

Background: AF recurs more frequently after catheter ablation in individuals with a high BMI than it does in those with a normal BMI. However, the association between AF recurrence and BMI may be influenced by race. The authors investigated the relationship between BMI and AF recurrence after catheter ablation in Japanese patients. Methods: They enrolled 726 consecutive patients with paroxysmal or persistent AF (241 patients classified as overweight/obese [BMI ≥25 kg/m2] and 485 classified as non-overweight/obese [BMI

The spawning area of the Japanese eel is located at the southern part of the West Mariana Ridge in the western North Pacific, but their spawning events have not been observed. To further understand Japanese eel spawning ecology, an interdisciplinary research survey by the R/V NATSUSHIMA (NT14-09, 14 May–4 June 2014) was conducted to detect spawning sites based on the seamount, salinity front, new moon and third quadrant (spawning south of front, west of ridge) hypotheses. Attempts were made to film spawning events with underwater camera systems and to consider if eels might be detected in hydroacoustic observations. Although no Japanese eels or spawning events were video-recorded and no eel aggregations could be clearly identified acoustically, three eggs were collected at two stations in the third quadrant region at or just south of 13° N on 26 and 27 May. Three or four days later, newly hatched preleptocephali were collected at two stations far to the south, including 224 at a station > 160 km southwest of the egg catches, and a few preleptocephali were caught at two stations closer to the egg stations. The eggs and southern preleptocephali were from discrete spawning events, which indicated that at least two spawning sites occurred in May 2014.

This study assessed the effects of diets supplemented with different types of chitin hydrolysate on larval growth of the Japanese eel Anguilla japonica. Larvae were reared for 26 days on artificial diets containing 2% of purified monomeric N-acetylglucosamine (NAG1), a mixture of mono-, di- and trimers (NAG3), a mixture of mono-, di-, tri-, tetra-, penta- and hexamers (NAG6), or a control diet. The larvae fed NAG3 and NAG6 grew significantly more rapidly than the control larvae (p 0.9). These results indicate that NAG3 is the most effective supplement for eel larvae. A dose–response analysis showed that the optimal level of NAG3 in the diet was around 1%. Although the biological activity of chitin hydrolysates in eel larvae remains unclear, part of these hydrolysates are likely utilized by eel larvae as components of glycosaminoglycan, a major constituent of their bodies. Alternatively, the hydrolysates may act as a bioactive substance, influencing fish health, or in the effective utilization of energy in eel larvae, enhancing their growth.

The effect of restoring sinus rhythm by pulmonary vein isolation (PVI) on the quality of life (QOL) of patients with persistent atrial fibrillation (PerAF) has not been adequately investigated. This study was performed to compare the changes in QOL after extended PVI between patients with PerAF and paroxysmal AF (PAF).Patients with PAF (n = 38) and PerAF (n = 22) who underwent their first PVI and developed no AF recurrence 6 months after PVI were enrolled. QOL surveys were performed at baseline and 6 months post-ablation using Short Form-36 surveys.The mental component summary score (MCS) (53.4 ± 10.2 to 56.5 ± 7.1, P = 0.019) and physical component summary score (PCS) (46.1 ± 10.6 to 48.5 ± 8.3, P = 0.015) improved after PVI in the PAF group. The PCS, but not the MCS, improved after PVI in the PerAF group (45.8 ± 7.9 to 51.5 ± 6.2, P < 0.001). Changes in the PCS were greater in the PerAF group than in the PAF group (8.6 ± 6.9 versus 2.8 ± 5.2, P = 0.009). Multivariate regression analysis demonstrated that a low baseline MCS and the type of AF (PAF) were independent predictors of an increased MCS and that a low baseline PCS and the type of AF (PerAF) were independent predictors of an increased PCS.The changes in QOL differed between PAF and PerAF after PVI. Although most patients with PerAF were asymptomatic before PVI, their improvement in physical QOL was greater than that in patients with PAF. Such beneficial effects on physical QOL are likely expected in patients with PerAF with a low PCS before PVI.

The efficiency of a new liquid-type diet for long-term rearing of Japanese eel larvae until metamorphosis was examined, as was the effect of diet viscosity on diet intake and on the survival and growth of early larvae. The highest intake of the experimental diet by 6- and 9-day post-hatch (dph) larvae occurred at viscosities of 20–50 mPa·s, much lower than the viscosity of the currently used slurry-type diet (ca. 2900 mPa·s). Long-term feeding trials for 259 days (n = 4) showed that overall survival rates of larvae (37–59%) fed a liquid-type diet with lower viscosity (40–680 mPa·s) were 2 to 3.4 times higher than the survival rates of larvae fed the slurry-type diet (11–25%). Because nutrients were diluted in the liquid-type diet, the growth of larvae fed this diet was slower after about 200 days and metamorphosis was delayed. However, the yield of glass eels was 1.1 to 3.2 times higher in larvae fed the liquid than the slurry diet. These findings suggest that feeding the liquid-type diet can result in the mass production of glass eels by ensuring high growth, survival and metamorphosis rates.

Early larval growth of the Japanese eel Anguilla japonica reared at five different water temperatures (19, 21, 23, 25, and 27 °C) is described for the first month post-hatching, a critical period of time in the culture of these sensitive larvae. After 3 weeks of culture, larvae reared at 27 °C attained the greatest total length and body height of all temperature treatments. Larvae reared at higher temperatures developed rapidly due to active feeding, despite higher metabolic costs. At lower temperatures of 19–21 °C, sudden mortality 12–16 days post-hatching coincides with the transition of larvae from endogenous to exogenous feeding. A linear relationship between water temperature and otolith diameter for cultured eel larvae otoliths suggests that the mean ambient water temperature experienced by wild larvae during their first month after hatching is about 23 °C. This temperature corresponds to mean water temperatures likely experienced by larvae during diel vertical migrations in the North Equatorial Current. We propose rearing early stage Japanese eel larvae at variable temperatures throughout the light/dark cycle to enhance their survival and growth in captivity.

To assist in detection of offshore spawning activities of the Japanese eel Anguilla japonica and facilitate interpretation of results of environmental DNA (eDNA) analysis in their spawning area, we examined the eDNA concentration released by each life history stage of artificially reared Japanese eels in the laboratory using quantitative real-time PCR (qPCR). We also compared eDNA concentrations between before and after artificially induced spawning activities. eDNA was not detected from three 30 L seawater tanks containing each single fertilized egg, but eDNA was found from other tanks each containing single individuals of larval stages (preleptocephalus and leptocephalus), juvenile stages (glass eel, elver and yellow eel) or adult stage (silver eel). The eDNA concentrations increased in the life history stages, showed a significant difference among all stages, and were positively correlated with the total length and wet weight. Moreover, the eDNA concentration after spawning was 10–200 times higher than that before spawning, which indicated that the spawning events in the ocean would produce relatively high eDNA concentration. These results in the laboratory suggested that eDNA analysis appears to be an effective method for assisting oceanic surveys to estimate the presence and spawning events of the Japanese eel in the spawning area.

Development of artificial production of glass eels still presents many problems to be solved. What and how to feed larvae is one of the most crucial problems for commercial mass production of glass eels. We evaluated a new liquid-type diet and feeding method against the conventional slurry-type diet by comparing the growth and survival of larvae in triplicate for 27 days after hatching. Larvae were fed by immersion in a liquid-type diet that was a 1.5 times dilution of the conventional slurry-type diet based on dogfish yolk spread over the bottom of the rearing tank. Larvae took more and denser liquid-type food in the intestine than the conventional slurry-type diet. Survival rates at 3 weeks after first feeding were about 90% in most experimental groups (5 groups) except one of three slurry-type diet groups (about 70%). Growth rates were 1.35 times higher in liquid-type diet groups (0.27 mm/day at 27 dph) than in conventional slurry-type diet groups (0.20 mm/day). These results suggest that the immersion feeding method in conjunction with the liquid-type diet has the potential to enable large scale production of glass eels by ensuring high growth and survival.

Hyaluronan (HA) is a main component of the highly hydrated extracellular body matrix of the larval stage of eels (leptocephalus). To determine the physiological and nutritional significance of HA in artificially reared larvae of the Japanese eel Anguilla japonica, HA and water content were measured at various larval stages in captivity. HA accumulated in the larval body with growth and water content also increased in parallel with HA. Almost all the accumulated HA was consumed during metamorphosis, suggesting HA plays a significant role in eel growth and metamorphosis. However, the amounts of HA and water were significantly lower in reared than in wild-caught larvae at the young stage, indicating a poorer nutritional condition of reared larvae, probably due to the deficient performance of currently used artificial diets. HA accumulation in reared larvae, however, eventually attained a level sufficient for metamorphosis by 250 days or more, and the glass eels of reared larvae had the same nutritional condition as that of wild glass eels. These findings are discussed with respect to the development of more effective artificial diets for rearing eel larvae.

The high mortality rate of reared Japanese eel Anguilla japonica larvae is largely due to lower growth rate and the higher rate of deformed larvae. To establish an effective rearing protocol for this species, we examined the effects of water temperature and feeding regimes on their growth and notochord kyphosis. Larvae at 165 days post hatching were reared for 28 days at mean temperatures of 24, 25 and 27 °C, and were fed 4 or 6 times per day. Larval growth rate was significantly higher in larvae reared at 24–25 °C and fed 6 times per day. However, growth rate was significantly reduced at 27 °C, suggesting a shortage of metabolic energy due to an elevated cost of the higher basal metabolic rate at higher temperatures and low nutritional performance of currently used artificial diet. Notochord kyphosis was promoted by elevated water temperature, and two-way ANOVA showed that water temperature and feeding frequency had combined effects on the deformity. These findings suggest the importance of concurrently manipulating both environmental and nutritional factors to produce healthy eel larvae in captivity.

The timing of downstream migrations of anguillid silver eels in relation to environmental factors in rivers has been examined using various types of data. Less is known about the factors that affect when silver eels leave estuaries and enter the sea or about the onset of the spawning migrations of eels living in brackish-water coastal areas. The timing of collections of Japanese eels, Anguilla japonica, in shoreline set nets in Mikawa Bay, Japan, were analyzed in relation to environmental variables such as water temperature, lunar phase, rainfall and wind speed over a 10 year period from 1997 to 2006. Higher catches of silver eels occurred during new moon periods in November and December as water temperatures decreased in the bay, and when the gonadosomatic index values of the eels were highest. Hurdle model analyses for clarifying the relationship between the catch of eels and environmental factors (lunar cycle, rainfall and wind) indicated the catches of eels were correlated with the two different environmental factors of wind strength 2 days earlier and lunar cycle, while rainfall was not selected by the model. This suggests that different factors are important for determining when eels migrate in coastal waters compared to during their downstream migrations in freshwater.

Myocardial ischemia/reperfusion injury worsens in the absence of nitric oxide synthase (NOS). Cilnidipine, a Ca2+ channel blocker, has been reported to activate endothelial NOS (eNOS) and increases nitric oxide (NO) in vascular endothelial cells. We examined whether pretreatment with cilnidipine could attenuate cardiac cell deaths including apoptosis caused by hypoxia/reoxygenation (H/R) injury. HL-1 mouse atrial myocytes as well as H9c2 rat ventricular cells were exposed to H/R, and cell viability was evaluated by an autoanalyzer and flow cytometry; eNOS expression, NO production, and electrophysiological properties were also evaluated by western blotting, colorimetry, and patch clamping, respectively, in the absence and presence of cilnidipine. Cilnidipine enhanced phosphorylation of eNOS and NO production in a concentration-dependent manner, which was abolished by siRNAs against eNOS or an Hsp90 inhibitor, geldanamycin. Pretreatment with cilnidipine attenuated cell deaths including apoptosis during H/R; this effect was reproduced by an NO donor and a xanthine oxidase inhibitor. The NOS inhibitor L-NAME abolished the protective action of cilnidipine. Pretreatment with cilnidipine also attenuated H9c2 cell death during H/R. Additional cilnidipine treatment during H/R did not significantly enhance its protective action. There was no significant difference in the protective effect of cilnidipine under normal and high Ca2+ conditions. Action potential duration (APD) of HL-1 cells was shortened by cilnidipine, with this shortening augmented after H/R. L-NAME attenuated the APD shortening caused by cilnidipine. These findings indicate that cilnidipine enhances NO production, shortens APD in part by L-type Ca2+ channel block, and thereby prevents HL-1 cell deaths during H/R.

Research efforts to achieve the production of artificial seedlings of the Japanese eel Anguilla japonica have progressed in recent decades. However, morphological deformities have been frequently observed in reared leptocephali and glass eels. We examined the effect of water current velocities (5.7–8.3 cm/s) on the body size and morphology of reared leptocephali and metamorphosed glass eels. As the current velocity increased, the size of leptocephali became smaller and the occurrence rate of notochord curvature increased. However, even in low velocities, water current had a long-term negative impact on their morphology. Sixty-five percent of metamorphosed glass eels had one of the eight types of vertebral deformities: compression, luxation, fusion, brachyspina, modification, lordosis, kyphosis, or scoliosis. Although their occurrence rate was unrelated to current velocity, there was a tendency for some deformities to be localised in a certain area of the vertebral column. In particular, compression frequently occurred in caudal vertebrae in faster currents. Most vertebral deformities began before the completion of metamorphosis. Therefore, appropriate management of the water current during the leptocephalus stage is important for establishing mass production of morphologically normal glass eels.

Wild anguillid eel larvae inhabit the ocean during their early life stages and never experience low-salinity water until the glass eel stage. The larvae show less mortality in half-diluted seawater than in full-strength seawater in captivity; however, physiological influences of environmental salinity on eel larvae have not been clarified. In this study, we compared the distributional and functional features of ionocytes between Japanese eel larvae acclimated to half-diluted and full-strength seawater. The mean tissue fluid osmolality in larvae acclimated to half-diluted seawater (300 mOsm/kg H2O) was slightly lower than in those (344 mOsm/kg H2O) acclimated to full-strength seawater. The density and opening size of ionocytes in the skin were not significantly different between the two salinities. Na+/K+-ATPase-immunoreactive ionocytes showed Na+/H+ exchanger-3 (NHE3) and cystic fibrosis transmembrane conductance regulator (CFTR) immunoreactions in their apical region and Na+/K+/2Cl- cotransporter-1 (NKCC1) immunoreaction in their basolateral region, suggesting that the skin ionocytes are involved in salt secretion in both salinities. In transmission electron microscopic observation, the ionocytes of larvae in full-strength seawater were characterized by the electron-dense cytoplasm, expanded tubular system and well-developed mitochondria, compared with those in half-diluted seawater, suggesting that the salt-secreting function was more activated in full-strength seawater than in half-diluted seawater. These results suggest that the energy metabolism cost of ion regulation could be lower in the intermediate salinity environment, which is closer to their osmolality than full-strength seawater. Hence, it is hypothesized that the saving of energy required for osmoregulation in half-diluted seawater could be favorable to better survival and growth of artificial eel larvae.

Because the post-larval (leptocephalus) survival rates of batches of Japanese eels vary widely, a useful indicator is needed to identify good-quality larval batches before the time of first feeding. This study therefore evaluated the effects on post-larval survival of early ontogenetic variables, including rates of fertilization, abnormal cleavage, hatching, survival during the larval stage until 5 days post hatching (dph), and deformities of individual larvae reared in wells of 48-well microplates. In addition, the survival rate of larvae reared in a 180-l mass rearing tank with flowing seawater was measured. Both simple and multiple linear regression analyses showed that none of the variables assessed by the microplate method correlated with post-larval survival, although the survival in the mass rearing tank at 5 dph was significantly associated with post-larval survival. These results suggest that early ontogenetic variables were likely strongly influenced by incubation methods, with the optimal method of identifying good-quality larvae being to measure the survival rate of mass reared rather than individually reared larvae. We suggest that larvae reared by the microplate method were likely subjected to excessively reduced environmental stress, due to the presence of antibiotics and the lack of interference between individuals, resulting in an overestimation of larval quality.

Association between pre-ablation levels of biomarkers of cardiac and endothelial dysfunctions, CHADS2, CHA2DS2-VASc, and APPLE scores and the recurrence of atrial fibrillation (AF) after radiofrequency catheter ablation has not been fully studied. A total of 254 patients with nonvalvular AF were prospectively followed for AF recurrence after a single ablation procedure. During a two-year follow-up period, AF recurred in 65 (25.6%) patients. Patients with AF recurrence had significantly greater baseline ln brain natriuretic peptide (BNP) than those without AF recurrence (P

One of the difficulties to rear Anguilla japonica larvae is the frequent occurrence of notochord deformities. We tested the effect of salinity on the occurrence of the deformities, because we have been using 50 % diluted seawater (50 % SW) for glass eel production, on the basis of the fact that intermediate salinity saves energy due to lower cost for osmoregulation and contributes higher survival and growth rates. We reared 6-day-old larvae in 50 and 100 % SW for 85 days and observed their morphology. The occurrence rate of deformed larvae, including kyphosis and scoliosis, was significantly higher in 50 % SW (35.8 %) than in 100 % SW (25.4 %), while survival rate was significantly higher in 50 % SW (69.8 %) than in 100 % SW (32.3 %) and growth in 50 % SW (mean body depth: 7.9 ± 5.3 mm) was better than in 100 % SW (6.8 ± 4.6 mm). We speculate that the most of severely deformed larvae could not survive in the tougher condition of 100 % SW, showing the lower occurrence of deformed larvae. Eventually, the yield of normal larvae after 85 days rearing was 1.9-fold higher in 50 % SW than in 100 % SW, implying that the advantage of 50 % SW for rearing eel larvae outweighs the risk of deformities.

The anguillid eels are catadromous fishes that migrate between marine and freshwater habitats. The long migration of eel larvae, called leptocephali, as long as thousands of kilometers in the ocean is important to determine their recruitment successes. The leptocephali in the ocean have a pelagic lifestyle totally different from the benthic one of glass eels and yellow eels in rivers. It is known that eel leptocephali have ionocytes on the body surface that may maintain ionic and osmotic status in the internal environment; however, detailed morphology and function of ionocytes in leptocephali are still unknown. In the present study, we aimed 1) to clarify the morphological features of the epidermis in Japanese eel Anguilla japonica leptocephali cultured in hyper-osmotic condition, and 2) to examine the ion-transporting functions of ionocytes of both leptocephali and yellow eels. Na+/K+-ATPase-immunoreactive ionocytes were distributed all over the body surface of leptocephali. Ionocytes were in contact with external environments through their apical membrane, which was located at the boundary of pavement cells. Na+/K+-ATPase-immunopositive cells were not observed in the skin of seawater-acclimated yellow eels. In ionocytes of the larval skin, the apical membrane appeared as a slightly projecting disk with a microvilli-like structure. Meanwhile, the apical membrane of gill ionocytes of yellow eels formed a concave surface. In ionocytes of leptocephali, mitochondria were enlarged and the tubular system was well developed, as compared with those of the gill of yellow eels. Ionocytes of leptocephali showed CFTR immunoreaction in their apical region and NKCC1 immunoreaction in their basolateral region, suggesting that the skin ionocytes are involved in salt secretion. These results support the notion that Japanese eel maintain their ion balance through skin ionocytes during early life stages, and that the skin ionocytes of leptocephali disappear in yellow eel stages after the formation of functional gills and gill ionocytes.

The onset of osmoregulation for seawater adaptation was examined during the early life stages of the Japanese eel. Ingested seawater was detected in the digestive tract by using fluorescent dextran as an inert marker. Ingested seawater remained in the forepart of the digestive tract at 0 and 1 days post hatching (dph), but reached the anus at 2 dph. Scanning electron microscope observations showed that the mouth appeared as a slit at 0 dph and developed into a hole-like shape at 2 dph. Expressions of Na+, K+, and 2Cl− cotransporter 2β (NKCC2β), and Na+ and Cl− cotransporter β (NCCβ) mRNAs were detected mainly in the intestine and rectum, respectively. These results are consistent with those of the adult eel, suggesting that the intestine and rectum are the sites of active ion absorption in larvae also. Expression levels of NKCC2β steeply increased from 4 to 6 dph, while NCCβ levels were highest on the day of hatching, presumably due to a maternal factor. The expression levels of NCCβ decreased by 3–4 dph and then increased to a constant status at 7 dph. Our findings confirmed that osmoregulation started as early as the day of hatching and stabilized within a week.

To clarify the role of thyroid function during metamorphosis from leptocephalus to glass eel in the Japanese eel, we examined the histology of the thyroid gland and measured whole-body concentrations of thyroid hormones, thyroxine (T4) and triiodothyronine (T3), and thyroid stimulating hormone β-subunit TSH (TSHβ) mRNA expression levels in five stages of artificially hatched eels (leptocephalus, early-metamorphosis, late-metamorphosis, glass eel, and elver). During metamorphosis, the inner colloid of thyroid follicles showed positive immunoreactivity for T4, and both T4 and T3 levels were significantly increased, whereas a small peak of TSHβ mRNA level was observed at the early-metamorphosis stage. Similarly, TSHβ mRNA levels were highest in the glass eel stage, and then decreased markedly in the elver stage. In contrast to TSHβ mRNA expression, thyroid hormones (both T4 and T3) increased further from the glass eel to elver stages. These results indicated that thyroid function in the Japanese eel was active both during and after metamorphosis. Therefore, the thyrotropic axis may play important roles not only in metamorphosis but also in subsequent inshore or upstream migrations. J. Exp. Zool. 321A: 357–364, 2014. © 2014 Wiley Periodicals, Inc.

The expression of peptide transporter 1 (PEPT1) was investigated at the different life stages of Japanese eel, Anguilla japonica. The cDNA encoding Japanese eel PEPT1 was cloned and sequenced. The hydrophilicity plot analysis of its deduced amino acid sequence showed high similarities with topological features of known PEPT1 molecules in other species. Tissue distribution analysis confirmed that PEPT1 mRNA was detected specifically in the anterior and posterior intestines of adult eel. In eel larvae at 13days post hatching (dph), PEPT1 mRNA expression was mainly detected in the intestinal tract regions. The trypsinogen mRNA was only detected in the gastric region including the pancreas. Intense immunoreaction for PEPT1 was observed in the apical membrane of the intestinal epithelial cells of both larval and adult eel. These results indicated that PEPT1 was an intestine-specific transporter, which was localized at the luminal side of the epithelial cells, suggesting that di/tri-peptide absorption via PEPT1 takes place in the eel intestine. According to the ontogenetic analyses by quantitative PCR, PEPT1 and trypsinogen mRNA expressions were simultaneously increased at 5-7 dph. It is thus assumed that nutrient absorption systems in the intestinal tracts of larvae become functional at this age.

Remarkable progress in techniques for maturation of adults and rearing of larvae has been achieved for the Japanese eel Anguilla japonica over the past 50 years, but recent efforts have not yet succeeded in the mass production of glass eels. This article reviews recent advances in techniques for artificial production of A. japonica glass eels. Successful new protocols for obtaining viable eggs and larvae of A. japonica are largely resulting from using artificially feminised eels instead of wild silver eels. The feminisation technique by administration of 17β-estradiol to glass eels not only provides an opportunity for using females as experimental broodstock throughout the year, but also accelerates their oocyte development or even increases the competence of females to respond to salmon pituitary extract. Induced spontaneous spawning with paired eels can improve the success rate for obtaining good-quality eggs compared with the traditional stripping-insemination method. As a result of the accumulation of field data on natural environmental conditions, such as an optimum temperature, where eel eggs and larvae were collected, the survival and growth rate of captive eel leptocephali have been much improved under these conditions. However, 50% diluted sea water (17.5 psu) that is far from the natural condition can result in better growth and survival performance in A. japonica leptocephali, possibly because it reduces the energy necessary for osmoregulation. Starvation can be a cue for triggering the onset of metamorphosis in A. japonica leptocephali, reducing the prolonged duration of the larval stage in captivity. To reach the mass production of glass eels at a commercial level, further improvement in quality of an artificial larval diet not containing eggs of the endangered shark Squalus acanthias is needed. The control of deformities in captive leptocephali and glass eels is also an important task. New techniques reducing the excessive use of exogenous hormones with parent eels should also be developed, to avoid public perception of an unhealthy product. If these techniques are completely established, we can exchange artificially produced glass eels with some part of the wild glass eels that are heavily exploited and provided to the eel aquaculture industry, and this can help to reduce the impact of eel consumption, which will contribute to the conservation of eel species worldwide.

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 30 cm in total length) were reared for 1.5 years in seawater at temperatures ranging from 10 to 20 °C before the experiments. Then, 141 randomly selected female eels (58 to 82 cm 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 400 μm) recorded in April 2003 had increased to maximum values of 30.0 and 650 μm, respectively, at the end of experiment, in March 2004. In late December 2003, 12 fish with oocytes measuring over 600 μm in diameter were selected and divided into an elevated temperature group from 6 to 10 °C and a control group of 6 °C for 43 days. 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 ± 46 μm 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.

We explored osmoregulatory ability and mechanisms of ion and water regulation in Japanese eel leptocephali. Tissue osmolality of leptocephali ranged from 360 to 540 mOsm/kg·H2O. Immunocytochemical observations revealed that Na+/K+-ATPase-immunoreactive mitochondrion-rich (MR) cells were distributed over the entire body surface of leptocephali. Using a fluorescent sodium indicator and the chloride test, we localized Na+ and Cl− secreting sites at the apical region of cutaneous MR cells. To further examine drinking behavior and water absorption in the intestine, leptocephali were exposed to seawater containing dextran labeled with Alexa Fluor. To calculate relative water absorption, fluorescent intensity was measured along the digestive tract. Whereas water was hardly absorbed in the stomach and intestine, water absorption predominantly took place in the rectum. Our findings indicate that Japanese eel exert hyposmoregulatory ability as early as during leptocephalus stages, secreting Na+ and Cl− through cutaneous MR cells and primarily absorbing water from ingested seawater in the rectum.

Usual diets for rearing leptocephalus larvae of Japanese eel Anguilla japonica include eggs of the endangered spiny dogfish Squalus acanthias (SE). We investigated the effects of alternative food materials, hen egg yolk (HEY) and exoskeleton-free (skinned) Antarctic krill (SAK), on the growth and survival of eel larvae. We found that feed comprising whole krill including exoskeleton (WAK) containing higher levels of fluoride (37.89 mg kg−1) was acutely toxic to eel larvae exposed to this alone. In contrast, extract from SAK containing lower concentrations of fluoride (4.25 mg kg−1) showed no apparent adverse effects. Growth of larvae fed a mixture of SE and SAK in a feed trial of 58 days [mean body weight (BW), 6.0 mg] was about twofold higher than that of larvae fed a mixture of SE and WAK (3.2 mg) (P

To obtain information about how water temperature affects the embryonic development of Japanese eel ( Anguilla japonica ) eggs, the developmental rates and hatching times of three lots of eggs were quantified at 16, 19, 22, 25, 28 and 31 °C. Hatching time was shortened at higher temperatures with eggs at 28 °C hatching within 23–28 h after fertilization, while eggs at 19 °C took 48–54 h for their hatching. At 22 and 25 °C, eggs hatched out within 35–43 h and 27–32 h, respectively. There was no successful hatching at 16 or 31 °C. The developmental stages until hatching were divided into morula, blastula, gastrula, eye vesicle and ear vesicle formation and heart formation. Development of the embryos were also faster at higher temperature especially after the gastrula stage, but the morphological features of each stage were the same at all water temperatures. The final developmental stage before the eggs died at 16 and 31 °C differed among the lots. Eggs maintained at 25 °C showed a high hatching rate (mean: 69%), compared to other water temperatures (mean: 12% at 19 °C, 32% at 22 °C, 4% at 28 °C). The results from present study indicate that the optimal temperature for egg incubation is around 25 °C, similar to the likely temperatures experienced by eggs and early larvae in the spawning area.

Technologies for rearing Japanese eel Anguilla japonica larvae (leptocephali) have improved markedly over the past decades. Notochord deformities, however, have been observed frequently in reared leptocephali. To learn more about these deformities, we studied notochord alterations in the leptocephalus stage of Japanese eels in captivity. Of 277 A. japonica leptocephali examined 170 to 307 days post hatching, 140 (50.5%) had kyphosis, a dorsal curvature of the notochord column; 4 (1.4%) had kyphosis-lordosis, a complication of the dorsal and ventral curvatures; and 21 (7.6%) had scoliosis, a lateral zig-zag curvature. Kyphotic leptocephali had various degrees of body curvature and often showed abnormal swimming behavior, continually whirling in the water column. The frequency of this whirling motion increased with increasing degree of body curvature. Even in the absence of whirling, the bodies of all reared larvae showed significantly greater curvature when compared with wild caught leptocephali, indicating that all reared larvae were potentially abnormal. Unlike leptocephali with scoliosis, those with kyphosis and kyphosis-lordosis often metamorphosed into glass eels, but retained their deformities, which would affect subsequent feeding behavior. Possible causes of these deformities, including nutritional imbalance, salinity, water temperature, and water current, are discussed.

We investigated the effects of low-salinity water on the growth, survival, and activity of artificially reared Japanese eel larvae (Anguilla japonica), proceeding from the assumption that such water quality saves energy due to lower cost for osmoregulation. We reared 5-day-old larvae in 0%, 10%, 30%, 50%, 70%, and 100% seawater (SW) with or without diet for 13 days. All larvae reared in 0% and 10% SW died within 6 days, while larvae in 70% and 100% SW survived until 9 days. Larvae in 30% and 50% SW further survived until 13 days without diet. Significant growth in body depth was observed in 30% and 50% SW after 7 days rearing with diet (0.65 ± 0.02 and 0.62 ± 0.02 mm, respectively) as compared with the initial size (0.49 ± 0.03 mm), while no significant growth was observed under the other salinity conditions examined. Larvae swam actively in the light (about 2000 lx) in 50%, 70%, and 100% SW, while they were apparently inactive in 0%, 10%, and 30% SW. The long-term rearing trial showed a 2.2-fold higher 2-month cumulative survival rate in 50% SW (18.2%) than in 100% SW (8.2%). The body depth of larvae in 50% SW (1.58 ± 0.47 mm) was also significantly larger than in 100% SW (1.32 ± 0.35 mm). These findings indicate that the intermediate salinity can result in better growth and survival performance in Japanese eel larvae.

The larvae of anguillid eels are termed leptocephali, among other reasons, because they differ greatly in morphology and physiology from other fish larvae. Leptocephali grow to large sizes but are transparent and fragile and have an unusual feeding strategy, so their behavior or ecology has rarely been studied. We used leptocephali, metamorphosing larvae and glass eels reared artificially from eggs to study the ontogenetic change in phototaxis in Japanese eel Anguilla japonica. By study- ing the early life history of this eel, our intent was to learn more about behavioral mechanisms asso- ciated with their vertical migration in the ocean and their long migration from the offshore spawning area to coastal waters. Horizontal distribution experiments found a clear negative phototaxis in the leptocephalus and metamorphosing larval stages, but no phototaxis was detected after metamor- phosis into glass eels. Vertical distribution experiments found that overhead lighting caused down- ward movement in leptocephali and metamorphosing larvae. When kept in darkness, leptocephali and metamorphosing larvae were distributed near the surface layer at night and at the bottom dur- ing daylight hours, suggesting an endogenous circadian rhythm that may control their diel vertical migration. Glass eels exhibited benthic distribution under any light conditions (0.0039 to 3.9 µmol quanta m -2 s -1 ), but showed random vertical distribution in darkness during both daytime and night- time, a behavior which appeared to be controlled only by light. Swimming speeds of leptocephali during horizontal movement and rising behavior were significantly greater than during diving behavior. These swimming behaviors and ontogenetic changes in phototactic behavior may help reg- ulate the vertical distribution and inshore migration of anguillid eel larvae in the ocean.

Many planktonic organisms have adaptations such as floats or lighter substances to obtain buoyancy to help them remain in the surface layer of the ocean where photosynthetic primary production occurs and food is most abundant. The almost totally transparent eel larvae, called leptocephali, are a unique member of the planktonic community of the surface layer, but their ecology and physiology are poorly understood. We conducted a comparative study on the specific gravity of planktonic animals including 25 taxa of 7 phyla of marine invertebrates and 6 taxa of leptocephali (vertebrate) to gain a broad perspective on the buoyancy of the eggs and larval stages of the Japanese eel. The specific gravity values of the various freshly caught marine invertebrate taxa varied widely from 1.020 to 1.425, but leptocephali had some of the lowest values (1.028–1.043). Artificially cultured live leptocephali had even greater buoyancies with specific gravities of 1.019–1.025 that were close to or lower than seawater, and their buoyancy showed ontogenetic changes among the different early life history stages. Leptocephali appear to have a unique mechanism of buoyancy control by chloride cells all over body surface through osmoregulation of body fluid contained in the extracellular matrix of transparent gelatinous glycosaminoglycans filling their bodies. This adaptation is likely a key factor for their survival by helping them to remain in the surface layer where food particles are the most abundant, while being transparent for predator avoidance. The ontogenetic change in buoyancy of eel eggs, leptocephali and glass eels likely enhances their larval survival, transport, and recruitment to terrestrial freshwater habitats.

ウナギ卵の孵化と仔魚の生残，成長に及ぼす銀イオンの影響を調べた。硝酸銀の濃度 0.1 mg/L 以上で孵化率は低下したが，仔魚の生残率は 1 mg/L でも 24 時間は 0 mg/L の対照区と変わらなかった。抗菌作用は 1 mg/L 以上で認められた。最大 1 mg/L の硝酸銀を水に 1 日 4 回添加し仔魚を飼育すると，飼育槽壁面の生菌数は銀添加区で有意に低かった。しかし，飼育水中の生菌数は銀添加区も対照区も差がなかった。長期飼育では，60 日齢まで添加区の生残率は対照区より有意に高く，銀添加の効果が認められた。

The effects of silvering state of wild female Japanese eels Anguilla japonica on the success of induced maturation and the following spawning were examined. Thirty-eight females, collected in Mikawa Bay, were divided into four stages based on their silvering state: yellow (Y1), late-yellow (Y2), silver (S1) and late silver eels (S2). Despite injections of salmon pituitary extract (SPE) through the standard technique, Y1 and Y2 eels did not respond to the treatment with undeveloped gonad (gonad-somatic index [GSI]: 0.3–0.9), and all these females died by 5 weeks, probably due to an abnormal physiological condition. Most S1 (81%) and S2 eels (100%) matured completely (GSI: 17.8–51.4), and finally spawned successfully (69% for S1, 89% for S2). S2 eels fully matured with oocytes of over 750 μm in diameter by significantly smaller number of injections of SPE (5–6 times) than the case of S1 eels (6–8 times). The amount of eggs released by S2 eels (0.65±0.11 g/fish per body weight [BW]) was significantly larger than those by S1 eels (0.54±0.09 g/fish per BW). There was no difference in fertilization and hatching rates between eggs released by S1 eels and those of S2 eels. These results indicate that the success of induced maturation and spawning in wild female Japanese eels depends on their silvering state, and matured eggs can be obtained efficiently through the use of S2 eels rather than other stages.

For efficient production of Japanese eel Anguilla japonica eggs, knowledge of the status of the sexual maturity of potential broodstock females is important because this status directly influences the time required to produce mature eggs by successive hormone doses. Here we apply an eye index (relative eye size) to evaluate the gonadal status of feminized A. japonica, which were induced by administration of estradiol-17β. Examination of gonad somatic and eye indexes of 267 feminized eels, cultivated for 12–56 months, revealed a significant correlation between these two indexes. Artificial maturation of 35 feminized eels showed that the number of hormone injections administered before ovulation was significantly lower as the eye index score increased, indicating availability of this noninvasive method of predicting sexual maturity of feminized eel. There was no correlation between eye index and fertilization rate, hatching rate, or larval survival rate, suggesting that sexual maturity before hormonal treatment does not affect egg quality.

人工催熟したウナギの採卵法の違いが，得られる卵仔魚の質に及ぼす影響を調べた。雌雄のペアリングによる昇温を伴う自発産卵法（n=12）と従来の水温一定の搾出媒精法（n=14）により得られた卵仔魚を比較したところ，受精率はそれぞれ 80±14%（平均±標準偏差）と 41±32%，孵化率は 62±23% と 31±29%，摂餌開始日齢の生残率は 54±22% と 27±25%，そして奇形率は 60±23% と 79±19%，と両者に有意差があった。昇温を伴う自発産卵法においては質の高い卵が得られるものと考えられた。

The ecological characteristics of 597 yellow and silver-stage Japanese eels, Anguilla japonica, were examined and compared among collection sites located at three different latitudes of Japan (Amakusa Islands, Mikawa Bay, and Sanriku Coast) to provide basic data on this unusual catadromous fish species. Eels were sexed and their total length, body weight, age, and growth rate based on otolith analysis was compared among sexes, stages, and collection sites. The overall sex ratio favored females (94%), but the sex ratio differed among the three locations. The frequency of females was highest in the coastal waters at Sanriku in the north (100%), next highest at Mikawa Bay in central Japan (95%), and lowest in the Amakusa Islands in the south (70%). Silver eel males ranged from 41.2-66.3 cm in length and 4-10 years in age, and silver eel females from 44.3-97.2 cm in length and 5-17 years in age. Female eels generally grew faster (8.7+/-2.2 cm/year) than males (6.4+/-2.6 cm/year), and the growth rate slowed in the older eels. The growth rate of A. japonica at all three sites was much faster than that of other temperate anguillid species (4 cm/year), and their age at maturation was younger than that of other temperate species (approximately 7 to50 years), suggesting this species has important ecological differences from other similar species.

We studied the influence of temperature on the spawning performance of artificially matured Japanese eels, Anguilla japonica, in captivity. We used routine hormone injections to bring females and males to maturity in separate aquaria. We recorded the behavior of three pairs of such hormone-treated matured eels in an aquarium (2 replicates) at four temperatures: 14, 18, 22, and 27 degrees C, respectively. They became active and frequently left the bottom swimming in the water column, and spawning events occurred. Females released eggs in the water column around the activity peaks. Males preceded females in reaching activity peaks (presumably the timing of sperm ejection and egg release), possibly resulting in the low fertilization we observed in this experiment. Males and females returned back to the aquarium bottoms and became quiet after spawning. On several occasions, male-female or female-female pairs were observed to 'cruise together' in the water column for several to tens of seconds prior to egg releasing, but no courtship behavior indicative of spawning such as pairing and chasing was observed in the eels in our study. Our results suggest that 18-22 degrees C might be the thermal preference for spawning for Japanese eels, which approximates the temperature range of the 500 m deep water layer around the Mariana Islands seamount area, the presumed spawning site for the Japanese eel.

Spawning behavior of artificially matured Japanese eels Anguillo japonica in captivity was investigated using a DVD Video image system. Following a routine hormone treatment technique for this fish, female eels were artificially matured by weekly intramuscular injections of salmon pituitary extracts (SPE) at a dosage of 40 mg kg(-1) BW for a total of 7-11 doses to induce ovarian maturation, while male eels received weekly intramuscular injections of human chorionic gonadotropin (HCG) at a dosage of 1000 IU kg(-1) BW for a total of 6-11 doses at 18 degrees C to induce testicular maturation in a separate aquarium. In this experiment, three pairs of such hormone-treated matured eels were acclimatized in seawater in 1.5 m(3) experimental aquaria with or without shelters at 20 degrees C for 24 h. Twenty four hours after the acclimatization terminated, the females received SPE injections to boost maturation and ovulation. Twenty four hours following these injections, the females received injections of HCG (1000 IU per fish, HCG injection) and 17 alpha-hydroxyprogesterone (2 mg per fish) to induce ovulation, while males were given HCG injections (1000 IU per fish, HCG injection) to induce spermiation. Video taping started after the 24 h acclimatization terminated and last for a total of 96 h. Before the HCG injections, both sexes were inactive, staying on the bottom or in shelters if available. Following these HCG injections, they became active and frequently left the bottom swimming in the water column. During the 24 h following HCG injections, activity accounted for 67% and 45% of the total activity in no shelter treatment for females and males, respectively, in comparison with 77% and 78% in shelter treatment. Activity was significantly more pronounced during this phase than during other phases for each sex in either shelter treatment. Egg release and sperm ejection occurred in the water column around the time eels' activity reached peaks. Eels either returned into the shelters or stayed motionlessly on the bottom of the aquaria after egg release and sperm ejection. Eight out of nine (89%) females in no shelter treatment spontaneously released eggs with a total of 11 batches 14-18 h following HCG injections, in contrast with four out of nine (44%) females releasing eggs for 4 batches 16-20 h in shelter treatment. Males arrived at activity peaks 11-13 h following HCG injections in no shelter treatment, 2-4 h ahead of the females (14-16 h), in comparison with 8-11 h in shelter treatment with 5-6 h ahead of the females (14-17 h). Courtship behavior indicative of spawning such as pairing, chasing and touching bodies was not observed in the eels in this study. However, on many occasions, eels of both sexes (male-female or female-female) were found to "cruise together" in water column for a short time period or frequently come together prior to releasing eggs and ejecting sperm, suggesting the possibility of group mating in artificially matured Japanese eels. (c) 2007 Elsevier B.V. All rights reserved.

The occurrence, distribution, and biological characteristics of non-native freshwater eels were analyzed using 5524 eels collected from 16 sites in Japan between 1997 and 2005. Three hundred seventy-four fishes (6.8%) were identified as non-native European eels, Anguilla anguilla, while the remainder (93.2%) were native Japanese eels, A. japonica. The European eel was found at 7 sites (44%), including 3 rivers, 2 freshwater lakes, one brackish lake, and one sea bay, suggesting a wide rage of habitat use. This variability of habitat use was also evidenced by the otolith microchemistry, which showed that they had lived in not only freshwater but also in seawater habitats. The sites with European eel were localized within the vicinity of southern Japan where a number of these eels were cultivated in the early 1970’s, suggesting that some had escaped from the culture ponds or were released intentionally into nearby natural waters. The large body size (mean total length: 803 mm), pigmented skin, enlarged eyes, and relatively matured gonads (mean gonad somatic index: 1.9) found in non-native European eels indicated that most had metamorphosed into the migratory silver phase, suggesting their ability to initiate spawning migration. However, the proportion of European eels in Mikawa Bay in 1997 was more than 12%, which decreased markedly to less than 2% after 2001, corresponding to the recent decline in import of European glass eels for aquaculture. This suggests that the population of European eels will decrease in Japanese waters in the future.