Circulating isotocin, not angiotensin II, is the major dipsogenic hormone in eels.

Angiotensin II (AngII) is generally known as the most important dipsogenic hormone throughout vertebrates, while two other neurohypophysial hormones, vasopressin and oxytocin, are not dipsogenic in mammals. In this study, we found that systemic isotocin, but not vasotocin, is the potent dipsogenic hormone in eels. When injected intra-arterially into conscious eels, isotocin, vasotocin and AngII equally increased ventral aortic pressure dose dependently at 0.03-1.0 nmol kg-1, but only isotocin induced copious drinking. The dipsogenic effect was dose dependent and occurred significantly at as low as 0.1 nmol kg-1. By contrast, a sustained inhibition of drinking occurred after AngII injection, probably due to baroreflexogenic inhibition. No such inhibition was observed after isotocin injection despite similar concurrent hypertension. The baroreceptor may exist distal to the gill circulation because the vasopressor effect occurred at both ventral and dorsal aorta after AngII but only at ventral aorta after isotocin. By contrast, intra-cerebroventricular (i.c.v.) injection of isotocin had no effect on drinking or blood pressure, but AngII increased drinking and aortic pressure dose dependently at 0.03-0.3 nmol per eel. Lesioning of the area postrema (AP), a sensory circumventricular organ, abolished drinking induced by peripheral isotocin, but not i.c.v. AngII. Collectively, isotocin seems to be a major circulating hormone that induces swallowing through its action on the AP, while AngII may be an intrinsic brain peptide that induces drinking through its action on a different circumventricular site, possibly a recently identified blood-brain barrier-deficient structure in the antero-ventral third ventricle of eels, as shown in birds and mammals.

North Equatorial Current and Kuroshio velocity variations affect body length and distribution of the Japanese eel Anguilla japonica in Taiwan and Japan.

The larval stage of Japanese eel travels a substantial distance over a long duration through the North Equatorial Current (NEC) and the Kuroshio, and the spawning behavior of mature eels leads to monthly arrival waves in eastern Taiwan between November and February. The total length (TL) of the glass eel relates to its larval duration and age; therefore, the TL can indicate the larval duration. The monthly mean TLs of eels along eastern Taiwan from 2010 to 2021 were used to estimate the batch age, and the recruitment patterns and relative abundances were compared. The TLs of glass eels followed a normal distribution, and the estimated ages were highly correlated with their mean TLs. Early recruit TLs were significantly greater than those of late recruits. The mean tracer drift time was longer in early recruitment months (November-December) than in later dates (February-March). The recruitment lag between Taiwan and Japan was approximately 1-1.5 months, with relative more abundance in Taiwan for the early recruits and in Japan for the late recruits. Speculated cohorts followed the main streams of the NEC and Kuroshio, and the monthly velocity changes of these currents could affect the mean TLs as well as the distribution patterns of Japanese glass eels in Taiwan and Japan.

Anguilliform Swimming Performance of an Eel-Inspired Soft Robot.

In this article, we propose a soft eel robot design using soft pneumatic actuators that mimic eel muscles. Four pairs of soft actuators are used to construct the eel robot body. Pulse signals with suitable shifting phases are utilized to control delivery of compressed air to the actuators in sequence to create a sinusoidal wave from head to tail of the robot body. A model of hydrodynamic forces acting on an anguilliform swimmer when moving in fluid was built to estimate the thrust force generated by the robot at different tail beat frequencies. Experimental data revealed that the generated thrust force was positively correlated with the beat frequency. Measured data showed that swimming efficiency depended on both generated thrust force and body posture in situ. At the beat frequency of 1.25 Hz, and air pressure at three segments from head to tail of 65, 50, and 30 kPa, respectively, the eel robot body showed the best cost of transport (COT) of 19.21 with velocity of 10.5 cm/s (or 0.198 body length per second [BL/s]), compared to the other's values of operation frequency and air pressure. We also found that control shifting phase strongly affects the swimming speed and COT. The robot body reached the highest velocity at around 19 cm/s (0.36 BL/s) with the COT of 10.72. Obtained result in this research would contribute to development of soft elongated swimming robot and enhance the knowledge on swimming performance of both robot and natural eels.

Some biological properties of spiny eel (Mastacembelus mastacembelus, Banks & Solander, 1794) living in the Upper Euphrates River Basin, Turkey.

This study was carried out to determine some bioecological characteristics of Mastacembelus mastacembelus, which is the only species of Mastacembelidae family living in Turkey. Fish samples were caught between 2014-2018 from Keban Dam Lake, one of the most important reservoirs of the upper Euphrates Basin. In totally, 348 Mastacembelus mastacembelus individuals were examined, including 178 males and 170 females. The age distributions were defined between the I-XV age groups. Total lengths ranged from 14.20 to 81.80 cm in males and from 15.60 to 77.30 cm in females. Total length-weight relationships were calculated as W = 0.0083 × TL2.6516 for males, W = 0.0043 × TL2.8310 for females and W = 0.0063 × TL2.7256 for all population, and the growth type was estimated as "negative allometric". The von Bertalanffy growth parameters for all individuals were computed as L∞ = 90.99, k = 0.13, t0 = - 0.45. The total (Z), natural (M), fishing (F) mortality rates and exploitation rate (E) were estimated as Z = 0.313, M = 0.270, F = 0.043 and E = 0.137, respectively. The length at first capture (Lc) was found as 50.72. The optimum, maximum and economic yields were calculated as E0.5 = 0.361; Emax = 0.776; E0.1 = 0.664, respectively.

18S rRNA gene sequences of leptocephalus gut contents, particulate organic matter, and biological oceanographic conditions in the western North Pacific.

Eel larvae apparently feed on marine snow, but many aspects of their feeding ecology remain unknown. The eukaryotic 18S rRNA gene sequence compositions in the gut contents of four taxa of anguilliform eel larvae were compared with the sequence compositions of vertically sampled seawater particulate organic matter (POM) in the oligotrophic western North Pacific Ocean. Both gut contents and POM were mainly composed of dinoflagellates as well as other phytoplankton (cryptophytes and diatoms) and zooplankton (ciliophoran and copepod) sequences. Gut contents also contained cryptophyte and ciliophoran genera and a few other taxa. Dinoflagellates (family Gymnodiniaceae) may be an important food source and these phytoplankton were predominant in gut contents and POM as evidenced by DNA analysis and phytoplankton cell counting. The compositions of the gut contents were not specific to the species of eel larvae or the different sampling areas, and they were most similar to POM at the chlorophyll maximum in the upper part of the thermocline (mean depth: 112 m). Our results are consistent with eel larvae feeding on marine snow at a low trophic level, and feeding may frequently occur in the chlorophyll maximum in the western North Pacific.

Srag Regulates Autophagy via Integrating into a Preexisting Autophagy Pathway in Testis.

Spermatogenesis is an essential process for producing sperm cells. Reproductive strategy is successfully evolved for a species to adapt to a certain ecological system. However, roles of newly evolved genes in testis autophagy remain unclear. In this study, we found that a newly evolved gene srag (Sox9-regulated autophagy gene) plays an important role in promoting autophagy in testis in the lineage of the teleost Monopterus albus. The gene integrated into an interaction network through a two-way strategy of evolution, via Sox9-binding in its promoter and interaction with Becn1 in the coding region. Its promoter region evolved a cis element for binding of Sox9, a transcription factor for male sex determination. Both in vitro and in vivo analyses demonstrated that transcription factor Sox9 could bind to and activate the srag promoter. Its coding region acquired ability to interact with key autophagy initiation factor Becn1 via the conserved C-terminal, indicating that srag integrated into preexisting autophagy network. Moreover, we determined that Srag enhanced autophagy by interacting with Becn1. Notably, srag transgenic zebrafish revealed that Srag exerted the same function by enhancing autophagy through the Srag-Becn1 pathway. Thus, the new gene srag regulated autophagy in testis by integrated into preexisting autophagy network.

Oxytocin-like signal regulates Lh cells directly but not Fsh cells in the ricefield eel Monopterus albus†.

The synthesis and release of LH and FSH in the pituitary of vertebrates are differentially regulated during gonadal development and maturation. However, the underlying neuroendocrine mechanisms remain to be fully elucidated. The present study examined the possible involvement of isotocin (Ist), an oxytocin-like neuropeptide, in the regulation of Lh and Fsh in a teleost, the ricefield eel Monopterus albus. The immunoreactive isotocin receptor 2 (Istr2) was shown to be localized to Lh but not Fsh cells. In contrast, immunoreactive isotocin receptor 1 (Istr1) was not observed in either Lh or Fsh cells in the pituitary. Interestingly, Lh cells in female ricefield eels expressed Istr2 and secreted Lh in response to Ist challenge stage-dependently and in correlation with ovarian vitellogenesis. Moreover, Ist decreased Lh contents in the pituitary of female fish, indicating its stimulatory roles on Lh release in vivo. The induction of Lh release by Ist in dispersed pituitary cells was blocked by a PLC or IP3R inhibitor but not by a PKA or PKC inhibitor, indicating the involvement of the IP3/Ca2+ pathway. Collectively, the above results indicate that isotocin may bind to Istr2 to stimulate Lh release via the IP3/Ca2+ pathway, and play important roles in the ovarian maturation in ricefield eels. Furthermore, the present study suggests a novel neuroendocrine mechanism underlying the differential regulation of Lh and Fsh in vertebrates.

Physiological and molecular responses to thermal stress in red cusk-eel (Genypterus chilensis) juveniles reveals atrophy and oxidative damage in skeletal muscle.

The red cusk-eel (Genypterus chilensis) is a native species with strong potential to support Chilean aquaculture diversification. Environmental stressors, such as temperature, may generate important effects in fish physiology with negative impact. However, no information exists on the effects of thermal stress in Genypterus species or how this stressor affects the skeletal muscle. The present study evaluated for the first time the effect of high temperature stress in red cusk-eel juveniles to determine changes in plasmatic markers of stress (cortisol, glucose and lactate dehydrogenase (LDH)), the transcriptional effect in skeletal muscle genes related to (i) heat shock protein response (hsp60 and hsp70), (ii) muscle atrophy and growth (foxo1, foxo3, fbxo32, murf-1, myod1 and ddit4), and (iii) oxidative stress (cat, sod1 and gpx1), and evaluate the DNA damage (AP sites) and peroxidative damage (lipid peroxidation (HNE proteins)) in this tissue. Thermal stress generates a significant increase in plasmatic levels of cortisol, glucose and LDH activity and induced heat shock protein transcripts in muscle. We also observed an upregulation of atrophy-related genes (foxo1, foxo3 and fbxo32) and a significant modulation of growth-related genes (myod1 and ddit4). Thermal stress induced oxidative stress in skeletal muscle, as represented by the upregulation of antioxidant genes (cat and sod1) and a significant increase in DNA damage and lipid peroxidation. The present study provides the first physiological and molecular information of the effects of thermal stress on skeletal muscle in a Genypterus species, which should be considered in a climate change scenario.

Swimming under elevated hydrostatic pressure increases glycolytic activity in gas gland cells of the European eel.

In spite of many decades of research, the spawning migration of the European eel Anguilla anguilla from the European coast to the Sargasso Sea remains a mystery. In particular, the role of the swimbladder as a buoyancy regulating structure is not yet understood. In this study, we exercised silver eels in a swim tunnel under elevated hydrostatic pressure. The transcriptome of gas gland tissue of these exercised eels was then compared to the known transcriptome of not exercised (control) silver eel gas gland cells. Due to the high infection rate of the eel population with the swimbladder parasite Anguillicola crassus, the comparison also included an exercised group of silver eels with a heavily damaged swimbladder, and we compared the previously published transcriptome of not exercised silver eels with a highly damaged swimbladder with the exercised group of silver eels with a heavily damaged swimbladder. The comparisons of unexercised (control) silver eels with exercised silver eels with functional swimbladder (EF), as well as with exercised silver eels with damaged swimbladder (ED), both showed a significant elevation in transcripts related to glycolytic enzymes. This could also be observed within the comparison of unexercised silver eels with a highly infected swimbladder with exercised eels with a damaged swimbladder (DED). In contrast to EF, in ED a significant elevation in transcript numbers of mitochondrial NADH dehydrogenase was observed. While in EF the transcriptional changes suggested that acid production and secretion was enhanced, in ED these changes appeared to be related to thickened tissue and thus elevated diffusion distances. The remarkable number of differentially expressed transcripts coding for proteins connected to cAMP-dependent signaling pathways indicated that metabolic control in gas gland cells includes cAMP-dependent pathways. In contrast to ED, in EF significant transcriptional changes could be related to the reconstruction of the extracellular matrix, while in ED tissue repair and inflammation was more pronounced. Surprisingly, in exercised eels hypoxia inducible transcription factor expression was elevated. In EF, a large number of genes related to the circadian clock were transcriptionally modified, which may be connected to the circadian vertical migrations observed during the spawning migration.

Cytological analysis of integumentary and muscular adaptations in three sand-dwelling marine teleosts, Ammodytes tobianus (Ammodytidae), Gorgasia preclara (Congridae) and Heteroconger hassi (Congridae) (Teleostei; Actinopterygii).

Sandy bottoms are a ubiquitous environment found from sea bottoms to intertidal and freshwater zones. They are inhabited by many invertebrates and vertebrates which have developed morphological and physiological adaptations to sustain life under these particular conditions. Sandy habitats exhibit three potential constraints: abrasion, hypoxia and mechanical resistance. Here, three teleost species living in sandy environments were investigated: Ammodytes tobianus (Ammodytidae), Gorgasia preclara and Heteroconger hassi (Congridae). These teleost fishes were studied for their integument and muscular systems, which are potentially subject to sand abrasion and hypoxia, respectively. Based on histochemistry and transmission electron microscopy, we found the complex mucus system of G. preclara and H. hassi consists of two types of goblet cells and one type of sacciform cell. The secretions of both species are made of complex polysaccharides. In contrast, the scaly integument of A. tobianus has only a few goblet cells and no sacciform cells. We also highlighted, by immunohistochemistry, that the epidermal cell proliferation was much higher for this latter species, potentially resulting from the high rate of sand abrasion when A. tobianus buries itself quickly in the substrate. For all species, the major muscle fibre type was revealed by histoenzymology and corresponds to fast glycolytic fibres followed by intermediate fibres with slow fibres in the lowest proportion. Ammodytes tobianus possesses the highest fast fibre proportion (about 87% for A. tobianus and 75-78% for both garden eels). Our results provide new insights into the previously poorly studied teleost species, such as G. preclara, and allow us to highlight the complex skin histology of both garden eel species. Furthermore, the previously unknown muscle typing of these three species was determined.

Marine Protection Induces Morphological Variation in the California Moray, Gymnothorax mordax.

The effectiveness of marine protected areas (MPAs) on the general health and conservation of species, habitats, and community interactions is of great interest to researchers, managers, and recreationalists. However, the ecological and behavioral diversity of vertebrate predators of southern California kelp forests limits our ability to make general conclusions about MPA effectiveness across a variety of species. Identifying and studying species with extreme feeding habits or prey-capture strategies may offer greater insight into predator-prey relationships and reveal the trophic importance of an animal in the larger community. Moray eels (family Muraenidae) have been shown to have morphological and behavioral adaptations that allow them to consume large prey whole, identifying them as important predators. From 2015 to 2018, we studied the health and feeding behavior of a long-lived, elusive, and benthic kelp forest predator, the California moray eel (Gymnothorax mordax). We trapped eels inside and outside of Blue Cavern Onshore State Marine Conservation Area, an MPA on the northwest side of Santa Catalina Island, CA which prohibits the take of any species. Over 4 years, we captured 1736 eels. Overall, we found that morays were longer, older, heavier, had higher body condition, and were found in greater abundance within the MPA. Although fish comprised the majority of their summer diet, morays outside of the MPA were consuming a more diverse set of fish, while kelp bass comprised more than half of the diet for morays inhabiting the MPA. Additionally, we found that morays within the MPA had larger relative vertical gape distances (VGDs) and narrower heads. Our recapture data support the high site fidelity of morays, indicating that their diet and morphology are influenced by their local community. While the majority of morays are thriving in the MPA, as suggested by their robust sizes and longevity, high abundance appears to result in higher frequencies of cannibalism, the presence of an undescribed disease, and lower growth rates. Our results suggest that the MPA affects the life history of morays and may select for an alternative feeding strategy in which eels develop larger VGDs, smaller adductor muscles, and a specialized diet which is presumably influenced by the local environment. In addition, observations of cannibalistic behavior and species-specific disease provide us with important insight into natural factors that may still regulate populations removed from anthropogenic disturbances such as fishing.

Effects of Diet and Intraspecific Scaling on the Viscera of Muraenid Fishes.

Diet has a strong influence on the morphology and physiology of vertebrates. Members of numerous fish clades have provided excellent comparative models for examining the effects of diet, primarily carnivory vs. herbivory, on organ systems. In this study, we comparatively examined the effects of carnivory, specifically independent evolutions of piscivory and durophagy, on body dimensions, organ topology, and organ proportions between nine moray species (Muraenidae). We found that organ placement via the anteroposterior organ positions differed between members in the two diet categories, although general organ topology is conserved. The stomach (31 - 55%) and intestine (68 - 76%) consistently occupied the majority of the body cavity irrespective of diet. Diet was shown to influence overall body dimensions and relative organ proportions across all moray species. Durophagous morays have shorter head lengths and body depths, and shorter heart, liver, gall bladder, and spleen lengths compared to piscivorous species. There was also greater variation in organ lengths among durophagous species than within piscivorous species. We attribute this greater variation in organ lengths to the multiple independent origins of durophagy within Muraenidae. Our single intraspecific comparison of the California moray, Gymnothorax mordax, a piscivorous species, revealed that all organs scale isometrically with body cavity length over ontogeny. The stomach grows proportionally with body cavity length and is the second longest organ in G. mordax at all ontogenetic stages, with the longest being the intestine. This suggests that morays can consume large quantities of prey or relatively large individual prey throughout their life history. In addition to scaling patterns of G. mordax, our study is the first to investigate the effects of diet and the intraspecific scaling patterns on the viscera of members of the Muraenidae, a clade of obligate carnivores that inhabit most marine ecosystems.

First Observation of a Spontaneously Matured Female European Eel (Anguilla anguilla).

This study reports on the first observation of a spontaneously matured female European eel. The 43-year-old eel, together with eleven other females, resided at an aquarium house since their capture in 2002 and stocking as glass eels in 1978. In June 2019, the girth of the belly of the female increased as a sign of oocyte maturation. The specimen had an estimated gonadosomatic index (GSI) of 47, only half of the oocytes were hydrated and matured, indicating that European eels are polycyclic batch spawners. The live eels of the cohort were still in the previtellogenic phase but their eye sizes were close to that of the matured eel. We hypothesize that substances released by other maturing and spawning fishes may have triggered puberty of the eel. This first observation, and the possibility of more eels maturing in the near future, provides a natural reference for the sexual maturation of the European eel.

Design and development of the efficient anguilliform swimming robot- MAR.

Propulsion of swimming robots at the surface and underwater is largely dominated by rotary propellers due to high thrust, but at the cost of low efficiency. Due to their inherently high speed turning motion, sharp propeller blades and generated noise, they also present a disturbance to maritime ecosystems. Our work presents a bio-inspired approach to efficient and eco-friendly swimming with moderate to high thrust. This paper describes the concept, development and experimental validation of the novel anguilliform robot MAR. With 15 elements making up the 0.5 m long propulsive section and driven by a single, speed-controlled brushless DC motor (BLDC), the robot creates a smooth continuous traveling wave for propulsion. Steering and autonomy are realized by an actuated head with integrated batteries that serves as a front-rudder. Almost neutral buoyancy paired with individually actuated pectoral fins furthermore enable submerged swimming and diving maneuvers. MAR accomplished high thrusts at a moderate power consumption in first performance tests. The achieved maximum velocity and the speed related efficiency (defined as the achieved speed over the power consumption m Ws-1) did not fulfill the expectations in the first tests (in comparison to commercial rotary thrusters), which can be largely attributed to the spatial limitations and an imperfect test setup. Nevertheless, the potential towards highly efficient and high thrust propulsion is visible and will be further investigated in future efforts.

The last stage in the life history of the European conger eel Conger conger: a transformation before death.

The taxonomic, morphological and meristic features of a dark eel caught by commercial trawling off the Gulf of Patti, southern Tyrrhenian Sea, Mediterranean Sea, February 17, 2017, showed it to be a female Conger conger. Histological analysis of gonads demonstrated that the individual was in a post-spawning phase. X-ray radiographs showed widespread decalcification of skeleton and teeth loss, confirming a strong mobilisation of somatic energy reserves needed for reproductive development.

Molecular mechanisms for intestinal HCO3- secretion and its regulation by guanylin in seawater-acclimated eels.

The intestine of marine teleosts secretes HCO3- into the lumen and precipitates Ca2+ and Mg2+ in the imbibed seawater as carbonates to decrease luminal fluid osmolality and facilitate water absorption. However, the hormonal regulation of HCO3- secretion is largely unknown. Here, mucosally added guanylin (GN) increased HCO3- secretion, measured by pH-stat, across isolated seawater-acclimated eel intestine bathed in saline at pH 7.4 (5% CO2). The effect of GN on HCO3- secretion was slower than that on the short-circuit current, and the time course of the GN effect was similar to that of bumetanide. Mucosal bumetanide and serosal 4,4'-dinitrostilbene-2,2'-disulfonic acid (DNDS) inhibited the GN effect, suggesting an involvement of apical Na+-K+-2Cl- cotransporter (NKCC2) and basolateral Cl-/HCO3- exchanger (AE)/Na+-HCO3- cotransporter (NBC) in the GN effect. As mucosal DNDS failed to inhibit the GN effect, apical DNDS-sensitive AE may not be involved. To identify molecular species of transporters involved in the GN effect, we performed RNA-seq analyses followed by quantitative real-time PCR after transfer of eels to seawater. Among the genes upregulated after seawater transfer, AE genes (draa, b, and pat1a, c) on the apical membrane, and NBC genes (nbce1a, n1, n2a) and an AE gene (sat-1) on the basolateral membrane were candidates involved in HCO3- secretion. Judging from the slow effect of GN, we suggest that GN inhibits NKCC2b on the apical membrane and decreases cytosolic Cl- and Na+, which then activates apical DNDS-insensitive DRAs and basolateral DNDS-sensitive NBCs to enhance transcellular HCO3- flux across the intestinal epithelia of seawater-acclimated eels.

Implantation of a New Micro Acoustic Tag in Juvenile Pacific Lamprey and American Eel.

Juvenile Pacific Lamprey and American eels were used for laboratory evaluations to determine potential effects from tag implantation. Telemetry technology has been identified as a way to obtain more detailed information on movement and behavior across a broader spatial scale than is possible with other known technology. The purpose of this method is to provide a detailed step by step instruction on tag implantation for both lampreys and eel. For laboratory studies using actively migrating juvenile Pacific Lamprey (120-160 mm), we determined that the presence of the tag did not alter the swimming ability between tagged and untagged Individuals or have any significant tag loss (<3%). Similar results were determined during laboratory testing of Yellow phase American Eels (113-175 mm). No mortality occurred during a 38-day holding period and there was minimal tag loss (3.8%). The presence of the tag did not have any significant effect on the swimming ability or survival of tagged eels compared to untagged controls and there was minimal tag loss.

Assemblage structure, vertical distributions and stable-isotope compositions of anguilliform leptocephali in the Gulf of Mexico.

In August 2007, October 2008 and September-October 2010, 241 Tucker trawl and plankton net tows were conducted at the surface to depths of 1377 m at six locations in the northern and eastern Gulf of Mexico (GOM) to document leptocephalus diversity and determine how assemblage structure, larval size, abundance and isotopic signatures differ across the region and with depth. Overall, 2696 leptocephali representing 59 distinct taxa from 10 families were collected. Five families accounted for 96% of the total catch with Congridae and Ophichthidae being the most abundant. The top four most abundant species composed 59% of the total catch and included: Ariosoma balearicum, Paraconger caudilimbatus, Rhynchoconger flavus and Ophichthus gomesii. Four anguilliform species not previously documented in the GOM as adults or leptocephali were collected in this study, including Monopenchelys acuta, Quassiremus ascensionis, Saurenchelys stylura and one leptocephalus only known from its larval stage, Leptocephalus proboscideus. Leptocephalus catches were significantly greater at night than during the day. Catches at night were concentrated in the upper 200 m of the water column and significantly declined with increasing depth. Leptocephali abundances and assemblages were significantly different between sites on the upper continental slope (c. 500 m depth) and sites on the middle to lower continental slope (c. 1500-2300 m). Sites on the lower continental slope had a mixture of deep-sea demersal, bathypelagic and coastal species, whereas upper-slope sites contained several numerically dominant species (e.g., A. balearicum, P. caudilimbatus) that probably spawn over the continental shelf and upper slope of the GOM. Standard lengths of the four dominant species differed between sites and years, indicating heterochronic reproduction and potential larval source pools within and outside of the GOM. Stable-isotope analyses (δ13 C and δ15 N) conducted on 185 specimens from six families revealed that leptocephali had a wide range of isotopic values at the family and size-class levels. Species in the families Muraenidae, Congridae and Ophichthidae had similar δ15 N values compared with the broad range of δ15 N values seen in the deep-sea families Nemichthyidae, Nettastomatidae and Synaphobranchidae. Stable-isotope values were variably related to length, with δ15 N values being positively size correlated in ophichthids and δ13 C values being negatively size correlated in A. balearicum and P. caudilimbatus. Results suggest that leptocephali feed in various water depths and masses, and on different components of POM, which could lead to niche partitioning. Ecological aspects of these important members of the plankton community provide insight into larval connectivity in the GOM as well as the early life history of Anguilliformes.

Differential uses of coral reef habitats by a poorly-known cryptic fish predator.

This study used otolith microchemistry to evaluate whether the moray eel Gymnothorax chilospilus uses different habitats throughout its life (mainly juvenile and adult phases). Of the most informative trace elements within otoliths (the twelve isotopes 23 Na, 25 Mg, 43 Ca, 55 Mn, 59 Co, 60 Ni, 63 Cu, 66 Zn, 86 Sr, 111 Cd, 138 Ba and 208 Pb) only three ratios of Ca (Na:Ca, Sr:Ca and Ba:Ca) were informative and therefore used in a multivariate regression-tree analysis. Using a multivariate partitioning, three main phases were described from profiles, including the larval life phase (leptocephali), the intermediate phase (longest section between the larval life phase and the terminal phase) and the terminal phase (final section i.e., the most recent months preceding the death of fish). According to concentrations of the three ratios to Ca, G. chilospilus can be separated into three groups during their larval life stage (very different in Sr and Na), four groups during the intermediate phase (few differences in Sr and Na) and three groups during the terminal phase (differences in Sr), illustrating that G. chilospilus inhabit different habitats during these three phases. Our results showed that the leptocephali encountered different oceanic water masses with fluctuating Sr:Ca ratios during the early larval phase. During the intermediate phase (main part of their life-span), they lived in lagoonal waters such as fringing reefs or reef flats of lagoonal islets, characterized by a lower Sr:Ca ratio. During the latter part of their life, approximately one third of G. chilospilus encountered more oceanic waters close to or at barrier reefs, suggesting possible movements of these fish along a coast-to-ocean gradient.

Faunal activity rhythms influencing early community succession of an implanted whale carcass offshore Sagami Bay, Japan.

Benthic community succession patterns at whale falls have been previously established by means of punctual submersible and ROV observations. The contribution of faunal activity rhythms in response to internal tides and photoperiod cues to that community succession dynamism has never been evaluated. Here, we present results from a high-frequency monitoring experiment of an implanted sperm whale carcass in the continental slope (500 m depth) offshore Sagami Bay, Japan. The benthic community succession was monitored at a high frequency in a prolonged fashion (i.e. 2-h intervals for 2.5 months) with a seafloor lander equipped with a time-lapse video camera and an acoustic Doppler profiler to concomitantly study current flow dynamics. We reported here for the first time, to the best of our knowledge, the occurrence of strong 24-h day-night driven behavioral rhythms of the most abundant species (Simenchelys parasitica; Macrocheira kaempferi, and Pterothrissus gissu). Those rhythms were detected in detriment of tidally-controlled ones. Evidence of a diel temporal niche portioning between scavengers and predators avoiding co-occurrence at the carcass, is also provided. The high-frequency photographic and oceanographic data acquisition also helped to precisely discriminate the transition timing between the successional stages previously described for whale falls' attendant communities.