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We assessed the effects of starvation, body size, and water temperature on the onset of metamorphosis in leptocephali of Japanese eel (Anguilla japonica Temminck and Schlegel, 1846) as determined by the morphological criteria of proportion, preanal length, and body depth to total length. Leptocephali of mean total length 55.6 mm that had been reared in captivity for 241 days from hatching were divided into unfed (n = 28) and fed (n = 30) groups in triplicate and reared for an additional 2 weeks. The mean percentage of larvae starting metamorphosis within 2 weeks was significantly higher in the unfed than in the fed groups (70% vs. 28.6%), suggesting that food deprivation acted as a cue for metamorphosis. The critical size for metamorphosis was a total length of 50-55 mm; smaller larvae did not start metamorphosis even in the absence of food, whereas larvae reaching that critical size were induced to undergo metamorphosis by starvation. The start of metamorphosis under unfed conditions was independent of diel-varying water temperature (day 23 °C; night 21-29 °C), suggesting a high plasticity in response to a wide range of environmental temperatures. These findings suggest methods for the efficient production of glass eels, as well as new insights into the mechanism of eel metamorphosis. Key words: freshwater eel, Anguilla japonica, leptocephalus, glass eel, metamorphosis, environmental factor. Nous avons evalue les effets de la privation de nourriture, de la taille du corps et de la temperature de l'eau sur le debut de la metamorphose chez les leptocephales d'anguille japonaise (Anguilla japonica Temminck et Schlegel, 1846), tel que determine par les criteres morphologiques de proportion, de longueur preanale et de profondeur du corps par rapport a la longueur totale. Des leptocephales de longueur totale moyenne de 55,6 mm qui avaient ete eleves en captivite pendant 241 jours apres leur eclosion ont ete divises en triplicats d'un groupe non nourri (n = 28) et d'un groupe nourri (n = 30) et eleves pour une periode additionnelle de deux semaines. Le pourcentage moyen de larves dont la metamorphose a debute durant ces deux semaines etait significativement plus eleve pour les groupes non nourris que pour les groupes nourris (70 % contre 28,6 %), ce qui semble indiquer que la privation de nourriture agissait comme declencheur de la metamorphose. La taille critique pour la metamorphose etait une longueur totale de 50-55 mm; meme en l'absence de nourriture, les larves plus petites n'ont pas commence leur metamorphose alors que, pour les larves qui atteignaient cette taille critique, la privation de nourriture provoquait le debut de la metamorphose. Le moment de ce dernier pour les larves non nourries etait independant de la variation journaliere de la temperature de l'eau (23 [degre]C le jour, de 21 a 29 [degre]C la nuit), ce qui suggere une plasticite elevee en reponse a une large fourchette de temperatures ambiantes. Ces resultats font ressortir des methodes permettant une production efficiente de civelles et elargissent les connaissances sur le mecanisme de metamorphose des anguilles. Mots-cles: anguille d'eau douce, Anguilla japonica, leptocephale, civelle, metamorphose, facteur du milieu. [Traduit par la Redaction], Introduction Larval metamorphosis in fish, characterized by dramatic remodeling of the larvae, occurs in only a few groups of ray-finned fishes, as well as in all lampreys (Youson 2004). Of [...]

Japanese eels spawn mainly during June-August. The larvae (leptocephali) then drift for 3-5 months before metamorphosing into glass eels. The recruitment season generally starts in southern East Asia in November and in northern areas in April the following year, a lag of ~5 months. However, analysis of otolith daily growth rings revealed only a 1-2-month difference in the mean leptocephalus stage between southern and northern East Asian samples. Experiments and field observation indicate that glass eels may starve, lose body weight, and remain in early pigmentation stage for a few months in cold waters. The time lag in recruitment can be accounted for by a longer leptocephalus stage combined with a low temperature-driven delay to upstream migration in winter. The leptocephalus duration and oceanic currents determine the dispersal locations up to the glass eel phase, while temperatures determine the timing of upstream migration time at each location., Author(s): Yu-San Han [sup.1] Author Affiliations: (1) grid.19188.39, 0000000405460241, Department of Life Science and Institute of Fisheries Science, College of Life Science, National Taiwan University, , 106, Taipei, Taiwan Introduction [...]

Adrenomedullin (AM), known as a multifunctional hormone in mammals, forms a unique family of five paralogous peptides in teleost fish. To examine their cardiovascular effects using homologous AMs in eels, we isolated cDNAs encoding four eel AMs, and named AM1 (ortholog of mammalian AM), AM2, AM3 (paralog of AM2 generated only in teleost lineage), and AM5 according to the known teleost AM sequences. Unlike pufferfish, not only AM1 but AM2/3 and AM5 were expressed ubiquitously in various eel tissues. Synthetic mature AM1, AM2, and AM5 exhibited vasodepressor effects after intra-arterial injections, and the effects were more potent at dorsal aorta than at ventral aorta. This indicates that AMs preferentially act on peripheral resistance vessels rather than on branchial arterioles. The potency was in the order of AM2 = AM5 >> AM 1 in both freshwater (FW) and seawater (SW) eels, which is different from the result of mammals in which AM1 is as potent as, or more potent than, AM2 when injected peripherally. The minimum effective dose of AM2 and AM5 in eels was 1/10 that of AM1 in mammals. The hypotension reached 50% at 1.0 nmol/kg of AM2 and AM5, which is much greater than atrial natriuretic peptide (20%), another potent vasodepressor hormone. Even with such hypotension, AMs did not change heart rate in eels. In addition, AM1 increased blood pressure at ventral aorta and dorsal aorta immediately after an initial hypotension at 5.0 nmol/kg, but not with AM2 and AM5. These data strongly suggest that specific receptors for AM2 and AM5 exist in eels, which differ from the AM1 receptors identified in mammals. calcitonin gene-related peptide; teleost; ventral aorta; dorsal aorta; vasodepressor action

Abstract: The reconstruction of individual life histories from chemical otolith measures is stated as an unsupervised signal-processing issue embedded in a Bayesian framework. This computational methodology was applied to a [...]

Diadromous fish often enter freshwater directly from seawater via fish ladders or channels built in estuarine dams. The oxygen consumption rates (OCR) of glass eel, Anguilla japonica, were determined using an automatic intermittent flow respirometer under various salinity and temperature regimes to physiologically explain this direct movement. The endogenous rhythm of the OCR in wild glass eels, freshly collected from estuaries, was nearly synchronous with the tidal pattern at the estuarine collection site. When the salinity was changed from 20 psu (12[degrees]C) at a constant temperature to that of freshwater, the OCR of the glass eels decreased by 21.6[+ or -]7.0% (mean [+ or -] SD) (P < 0.05), showing a dampened rhythm for about 48 h. After this period of impediment, the glass eels resumed normal metabolic activity. Direct migration from seawater to freshwater under constant temperature would result in a severe physiological stress for these glass eels for about two days. When the glass eels were exposed to a cyclic change in water temperature of 2[degrees]C 26 [h.sup.-1], as they encounter in estuaries, and then were introduced to freshwater abruptly, the OCR rhythm corresponded to the cyclic changes in water temperature after exposure to freshwater. Under these conditions, the mean OCR of the glass eels had a small difference before and after exposure to freshwater. These data explained how glass eels can directly move from sea water into the freshwater without any apparent metabolic stress in the estuaries showing cyclic change in water temperature ([DELTA]t = 2[degrees]C)., Introduction Diadromous fish migrate between the sea and river at least twice in their lives. During this migration, the fish experience physiological stress due to the salinity changes that they [...]

Abstract: Several basic tenets of otolith research have been questioned recently with regard to eel metamorphosis. Specifically, some researchers have suggested that otolith increment formation is not daily, and otolith [...]

Complementary DNAs encoding homologs of the mammalian aqua-glyceroporins (termed AQPe) and aquaporin-1 isoforms (termed AQP1) were isolated from the European eel. The AQP amino acid sequences share 35-54% identity with other known human AQPs. Although AQPe mRNA expression was approximately equivalent along the entire length of the gut, AQP1 expression was the highest in the posterior/rectal segment. Seawater (SW) acclimation increased AQP1 mRNA abundance by 5- and 17-fold in the anterior, 14- and 23-fold in the mid-, and 9- and 7-fold in the posterior/rectal gut regions of yellow and silver eels, respectively. SW acclimation had an effect on AQPe mRNA expression only in the midintestine of silver eels, where a small but significant 1.7-fold increase in abundance was measured. Western blots using an eel AQP1-specific antibody identified the presence of a major immunoreactive 28-kDa protein, primarily within the posterior/rectal segment. A 3-wk SW transfer induced an increase in AQP1 protein abundance in all intestinal segments, with the posterior/rectal region still expressing protein levels ~40- and 8-fold higher than the anterior and mid-segments, respectively. Strong AQP1 immunofluorescence was detected within the vascular endothelium in both freshwater (FW)- and SW-acclimated eels and in the epithelial apical brush border in the posterior/ rectal gut regions of SW-acclimated eels. Cortisol infusion into FW eels had no effect on intestinal AQPe mRNA expression but induced increases in AQP1 mRNA and protein levels. These results provide evidence for the presence of a SW-induced and steroid-regulated AQP water channel pathway within the intestine of the European eel. Anguilla anguilla; gastrointestinal tract; AQP1; AQPe; corticosteroid

The early life history of the American conger eel, Conger oceanicus, was studied using otolith microstructure and chemical composition in metamorphosing leptocephali collected from New Jersey estuarine waters. The age of leptocephali was estimated by counting daily growth increments. Age of early metamorphosing leptocephali at recruitment to the estuary ranged from 155 to 183 days, indicating that migration of conger eel leptocephali from their oceanic spawning ground to the estuary requires 5-6 months. Back-calculated hatching dates suggest that the spawning season lasted 3 months, from late October to mid-December. However, in the late metamorphic leptocephali, the presence of an unclear peripheral zone in the otolith prevents the accurate estimation of the larval stage duration. The calcium content was almost constant throughout the otoliths. Both strontium and Sr:Ca ratios increased with age, but dramatically decreased at age 70-120 days. The otolith increment width also showed a marked increase at the same ages, indicating the onset of metamorphosis. A negative correlation between age at metamorphosis and otolith growth rate indicates that faster growing leptocephali arrive at the estuary earlier than slower growing ones. A close relationship was also found between age at recruitment and age at metamorphosis, suggesting that individuals that metamorphosed earlier were recruited to the estuary at a younger age. This larval migration pattern appears to be similar among anguilliform fishes.

A total of 29 specimens of the anguillid leptocephali Conger conger were collected by the R.V. 'Arquipelago', Department of Fisheries and Oceanography, University of Azores, in the waters south of the central group of the Azores Islands in October 1999. The meristic counts, morphologic features and pigmentation patterns of the leptocephali agree with the descriptions by other authors of this species. Leptocephali were found to range from 51.5 to 126.5 mm length and show a positively skewed distribution. The somatic growth rate (0.31 mm [day.sup.-1]), estimated from the linear regression of length on age, falls within the ranges reported by several authors for other anguilliform species. Back-calculated hatching dates from the otolith microstructure suggests a long spawning season, from January to July, with one visible annual peak, occurring in summer. The analysis of our collection data in light of the current physical oceanographic knowledge of the NE Atlantic suggests that it is unlikely that the Azorean specimens came from the Mediterranean, unless the larvae were capable of very active and oriented swimming; thus the existence of another spawning place for this species somewhere near the Azores Archipelago is probable.

For the first time the autonomous free-fall vehicle AUDOS was deployed at low latitudes in the northeast Atlantic Ocean. Observations of deep demersal fishes attracted to baited cameras were made at three stations near upwelling areas off West Africa: Canaries (27[degrees]20'N, 16[degrees]59'W), Cape Verde Terrace (17[degrees]45'N, 20[degrees]30'W), and Cape Verde Abyssal Plain (15[degrees]00'N, 20[degrees]30'W). The grenadier Coryphaenoides (Nematonurus) armatus was the main species attracted to the bait. Other fish species observed at bait were the eel Histiobranchus bathybius, a zoarcid, and the ophidiids Barathrites iris and Spectrunculus grandis. A comparison was made between this study area and the stations Porcupine Abyssal Plain (48[degrees]50'N, 16[degrees]30'W), which is eutrophic, and Madeira Abyssal Plain (31[degrees]00'N, 20[degrees]00'W), which is oligotrophic. These are situated on either side of a proposed faunal divide at 40[degrees]00'N with a high abundance of large species of rattails to the north and lower biomass of smaller fish species to the south. This study revealed a high abundance of large C. (N.) armatus at 17[degrees]00'N, which is a violation of this putative zoogeographic divide. It is suggested that high primary productivity and upwelling off West Africa sustain this assemblage of deep demersal fishes.

The natriuretic peptide system of a euryhaline teleost, the Japanese eel (Anguilla japonica), consists of three types of hormones [atrial natriuretic peptide (ANP), ventricular natriurehc peptide (VNP), and C-type natriuretic peptide (CNP)] and four types of receptors [natriuretic peptide receptors (NPR)-A, -B, -C, and -D]. Although ANP is recognized as a volume-regulating hormone that extrudes both [Na.sub.+] and water in mammals, ANP more specifically extrudes [Na.sub.+] in eels. Accumulating evidence shows that ANP is secreted in response to hypernatremia and acts to inhibit the uptake and to stimulate the excretion of [Na.sub.+] but not water, thereby promoting seawater (SW) adaptation. In fact, ANP is secreted immediately after transfer of eels to SW and ameliorates sudden increases in plasma [Na.sub.+] concentration through inhibition of drinking and intestinal absorption of NaCl. ANP also stimulates the secretion of cortisol, a long-acting hormone for SW adaptation, whereas ANP itself disappears quickly from the circulation. Thus ANP is a primary hormone responsible for the initial phase of SW adaptation. By contrast, CNP appears to be a hormone involved in freshwater (FW) adaptation. Recent data show that the gene expression of CNP and its specific receptor, NPR-B, is much enhanced in FW eels. In fact, CNP infusion increases [sup.22]Na uptake from the environment in FW eels. These results show that ANP and CNP, despite high sequence identity, have opposite effects on salinity adaptation in eels. This difference apparently originates from the difference in their specific receptors, ANP for NPR-A and CNP for NPR-B. VNP may compensate the effects of ANP and CNP for adaptation to respective media, because it has high affinity to both receptors. On the basis of these data, the authors suggest that the natriuretic peptide system is a key endocrine system that allows this euryhaline fish to adapt to diverse osmotic environments, particularly in the initial phase of adaptation. atrial natriuretic peptide; ventricular natriuretic peptide; C-type natriuretic peptide; membrane guanylyl cyclase; water and electrolyte balance; molecular evolution; functional evolution; volume regulation; sodium regulation; Anguilla japonica

Research has been conducted on the Anguilla leptocephali of western Pacific. The microstructure and michrochemistry of the leptocephali' otolith have been investigated in examining the early life-history characteristics of tropical eels and the results are presented.

Strontium (Sr) and calcium (Ca) contents in the otoliths of yellow and silver European eels [Anguilla anguilla (L.)] collected from coastal waters of the Baltic Sea and a freshwater lake in Sweden were examined by wavelength dispersive X-ray spectrometry with an electron microprobe. The mean Sr/Ca ratios from elver check to otolith edge were significantly higher for the eels from coastal waters (5.39 [+ or -] 1.09 [per thousand]) than for those from the lake (0.71 [+ or -] 0.89 [per thousand]). The evidence indicates that European eels in the Baltic Sea do not necessarily migrate into freshwater streams during the growth phase.

Otolith microstructure and microchemistry were examined in juveniles of American (Anguilla rostrata) and European (A. anguilla) eels. Otolith increment width markedly increased from age 132 to 191 d (156 [+ or -] 18.9 d; mean [+ or -] SD) in A. rostrata and 163 to 235 d (198 [+ or -] 27.4 d; mean [+ or -] SD) in A. anguilla, both of which were coincident with drastic decreases in otolith Sr:Ca ratios, suggesting that metamorphosis from leptocephalus to glass eel began at those ages in each species. The duration of metamorphosis was estimated to be 18 to 52 d from otolith microstructure, for both species studied. Ages at recruitment were 171 to 252 d (206 [+ or -] 22.3 d; mean [+ or -] SD) in A. rostrata and 220 to 281 d (249 [+ or -] 22.6 d; mean [+ or -] SD) in A. anguilla. In these two species, positive linear relationships were found in ages between the beginning of metamorphosis and recruitment, suggesting that early metamorphosing larvae recruited at younger ages. Duration of the leptocephalus stage to recruitment in A. anguilla was about 40 d longer than that in A. rostrata. The geographical segregation between the two species in the Atlantic Ocean seems to be involved in the differences in the duration of the leptocephalus stage (age at metamorphosis).

Experiments were conducted to characterize the chloride cell subtypes in the gill epithelia of the Japanese eel Anguilla japonica and to examine the kinetic changes of these cells after transfer from freshwater to seawater. The cell size, cellular granularity and cell autofluorescence was analyzed using multiparameter flow cytometry. Results showed that new subtypes of transitory chloride cells appeared within 2-4 days after entering seawater.

Vibrio vulnificus serovar E strains from aquatic habitats in Taiwan that are not virulent to eels have been isolated. Polymerase chain reaction of the cytolysin-hemolysin gene was used in studying the strains. Tryptone soya agar and tryptone soya broth were used as culture substrates. The Vibrio samples were obtained from water and oysters and are different from eel virulent strains in their fermentation, utilization of mannitol, ribotyping after HindIII digestion and susceptibility to eel serum.

Eels adapted to either freshwater or seawater were used in the investigation of the effects of atrial natriuretic peptide (ANP) on drinking and the levels of angiotensin II. Results reveal that ANP decreased both drinking rate and angiotensin II levels in eels although the magnitude of reduction was greater in freshwater-adapted eels. Whether the reduction in drinking rate was secondary to ANP or the reduction in angiotensin II levels was not established.

To investigate the capacity of the myomeric muscles to actively change the stiffness of the body during bending, mid-caudal sections (spanning two to three intervertebral joints) of intact, freshly-killed American eels, Anguilla rostrata, were dynamically bent (3 Hz, ± 4% maximal muscle strain) using the whole-body workloop technique. Following unstimulated cycles, the left- and right-sides of the tausculature were alternately stimulated at supra-maximal voltages and at eight different phases relative to the strain cycle of the muscle. The body's flexural stiffness (N[m.sup.2]) increased maximally by a factor of three relative to that when the muscles were unstimulated. The net external work (J [kg.sup.-j]) needed to bend the body decreased maximally by a factor of seven relative to that when the muscles were unstimulated. Both of these mechanical features varied sinusoidally with changes in the phase of the stimulus. Stimulus phase of caudal muscle in live swimming eels, taken from other studies, leads to the prediction that the caudal muscles increase body stiffness and produce net positive mechanical work simultaneously during steady forward swimming. The association of increased body stiffness and net positive muscle work, and the occurrence of maximal net muscle power output at a stimulus phase of 325 ° (as the muscle segment lengthens), suggests that net positive power is produced, in part, using an elastic strain energy mechanism., INTRODUCTION In vertebrates, studies of locomotor dynamics have broadened our view of muscle function beyond the classical model of forceful shortening. For example, measurements of muscle activity patterns (electromyography, 'EMG') [...]

Brush-border membrane vesicles isolated from the euryhaline Anguilla anguilla were analyzed to determine the mechanisms of electroneutral anion exchange across the luminal membrane. Analysis of luminal bicarbonate translocation in isolated eel brush-border membranes indicated the presence of a Cl-/bicarbonate exchange that operates at the apical level of the eel kidney absorbing cells. The antiporter also worked in conjunction with an Na+/H+ exchanger during fluid homeostasis in euryhaline eels.

The mechanisms of intestinal peptide transport in European yellow eels were analyzed to determine the role of hydrogen-ion concentration (pH) and membrane potential on the kinetic properties of intestinal transport. Analysis of intestinal brush border membrane vesicles (BBMV) from European yellow eels indicated the presence of increased H+-glycyl-L-proline uptake after the application of negative membrane potential. However, the H+-glycyl-L-proline cotransport was inhibited by cephalexin in the BBMV of European yellow eels.

The cardiac tissue of rainbow trout, cod, eel and freshwater turtle was analyzed to determine changes in cardiac mechanical performance and high-energy phosphate after the inhibition cellular energy liberation. Trout myocardium exhibited the highest decrease in cardiac tissue twitch tension after 30 minutes of anoxia while turtle myocardium exhibited the lowest decrease in cardiac twitch tension. The decrease in cardiac twitch tension is due to the high levels of intracellular high-energy phosphate which was mediated by the decrease in adenosine triphosphatase levels.

The physiology and binding sites of atrial natriuretic peptide (ANP) in seawater eels injected with 125I-labeled ANP were analyzed by utilizing whole body autoradiography and microautoradiography. In vitro autoradiography indicated the presence of dense concentrations of localized ANP binding in the gills of the seawater eels. The branchial ANP binding sites are composed of natriuretic peptide receptor-C (NPR-C) as exhibited by the inhibition of 125I-rat ANP binding to the trout gill by SC-46542 ligand of NPR-C.

A study was conducted on the removal of polychlorinated biphenyls and other organochlorine compounds from yellow eels under natural conditions. Results showed that elimination half-lives are in the order of years. Higher chlorinated chlorobiphenyls did not show signs of elimination during an eight-year period. It was determined that using eels as biomonitors is an important option for passive biological monitoring. It was also concluded that reducing contamination levels through depuration in clear water is not viable for commercial eel fisheries.

Leptocephali species assemblages in subtropical convergence zone (STCZ) of Sargasso sea are clustered near the southern fronts and western transects, and are large in size. The species do not occur in the mixed convergence zone water in the northern front regions. Frontal jets in the STCZ cause an eastward flow of the leptocephali.

A studey of charge translocation and phosphorylation kinetics during the pre-steady state of the NaK-ATPase reaction cycle involved time-resolved measurements of NaK-ATPase containing microsomes derived from the electric organ of Electrophorus electricus. A rapid electrogenic transition from E1P to E2P occurs after electroneutral ATP release, ATP and caged ATP binding, and exchange and phosphorylation.

This study was undertaken to isolate groups of eel (Anguilla japonica) intestinal cells undergoing active endocytosis in vivo and to localize these cells within the intestinal epithelium. A monoclonal antibody (8F1) of the immunoglobulin M class containing kappa light chains was raised against such endocytic cells. Ninety-three percent of the 8F1-positive cells absorbed fluorescent isothiocyanate-conjugated dextran from the intestinal lumen in vivo during a 30-min incubation, and they retained the ability to absorb dextran in vitro. The 8F1-positive cells constitute about 15% of the whole dissociated, macromolecule-absorbing cells. This suggests that other types of endocytic cells exist in the epithelium. The 8F1-positive cell can internalize fixed Vibrio anguillarum in vivo. Immunohistochemical observations demonstrated that 8F1-positive cells are very few in number and are located exclusively in the surface epithelium of the intestine. Thus these cells may well be specified phagocytic cells, different from those playing a basic nutritional role.

The growth history and age at recruitment of Anguilla anguilla are studied, based on growth increments in sagittal otoliths. Results show that the otolith has a typical sequential growth pattern with three steps, namely, moderate, slow and finally increasing growth rate. Moreover, microstructural examination of sagittae and increment enumeration is presently the most reliable technique for studying the growth rate of fish larvae.