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Photographs showing typical head and jaw shapes of many types of anguilliform leptocephali. These taxa are Anguilla marmorata (A), Ariosoma major (B), Heteroconger hassi (C), Conger sp. (D), Bathycongrus sp. (E), Gnathophis sp. (F), Muraenesox cinereus (G), Serrivomeridae sp. (H), Muraenidae sp. (I), Chlopsidae sp. (J), Nettenchelys sp. (K), and Synaphobranchinae sp. (L), Ilyophinae, Synaphobranchidae (M), Eurypharynx pelecanoides (N), Cyema atrum (O). Photos are reprinted from Miller and Tsukamoto (2004).
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... exhibit a wide variety of body shapes that range from very long and thin to deep, with rounded or pointed tails (Fig. 2). Head shapes also vary greatly ( Fig. 3; but see be- low). Maximum sizes of leptocephali can range from about 50 mm to greater than 300 mm (total length) (Castle 1984;Smith 1989a;Böhlke 1989b), but they remain transparent and very fragile regardless of their size or body shape until they metamorphose into juvenile ...
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... such as a thickening of the head, enlargement of the olfactory organ, and a loss of the teeth (Figs. 20B, 33, 34). In many nettastomatid leptocephali the olfactory rosette becomes very enlarged and elongate during metamorphosis (Smith and Castle 1982). In some metamorphos- ing muraenid leptocephali, the gills become larger and are visible (Fig. 34), whereas no gills are typically seen in premetamorphic leptocephali (Figs. 14, 15). The other major changes that occur during metamorphosis are that the gut and the origins of the dorsal and anal fins move forward, as can be seen in Ariosoma gilberti from the eastern Pacific ( Fig. 35) and in Conger oceanicus from the Atlantic coast of ...
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... leptocephali, the gills become larger and are visible (Fig. 34), whereas no gills are typically seen in premetamorphic leptocephali (Figs. 14, 15). The other major changes that occur during metamorphosis are that the gut and the origins of the dorsal and anal fins move forward, as can be seen in Ariosoma gilberti from the eastern Pacific ( Fig. 35) and in Conger oceanicus from the Atlantic coast of New Jersey (Fig. 36). Because the gut is moving forward with tissue being reabsorbed, the larvae do not feed during metamorphosis ). The relative position of the gut as it moves forward typically has been used as an indicator of the metamorphic stage of leptocephali (e.g. Lee and Byun ...
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... whereas no gills are typically seen in premetamorphic leptocephali (Figs. 14, 15). The other major changes that occur during metamorphosis are that the gut and the origins of the dorsal and anal fins move forward, as can be seen in Ariosoma gilberti from the eastern Pacific ( Fig. 35) and in Conger oceanicus from the Atlantic coast of New Jersey (Fig. 36). Because the gut is moving forward with tissue being reabsorbed, the larvae do not feed during metamorphosis ). The relative position of the gut as it moves forward typically has been used as an indicator of the metamorphic stage of leptocephali (e.g. Lee and Byun 1996;Otake et al. 1997;Bell et al. 2003;Kimura et al. 2004). The sensory ...
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... pores on the head and the nostrils of some species begin to form during the metamorphosing leptocephalus stage (Figs. 11, 20B, 33). In species with markedly different head shapes such as the mesopelagic Nemichthys that have long curved jaws, the jaws appear to rapidly extend forward even when the larvae are still in the leptocepha- lus stage (Fig. 33B). This also occurs in serrivomerid leptocephali (Beebe and Crane 1936;Miller and Tsukamoto 2004). A major enlargement of the olfactory organ is apparent in the metamorphosing synaphobranchid in Fig. 33A. Red blood cells begin to form in at least some late stage metamorphosing leptocephali such as Derichthys serpentinus (Fig. 37B), or ...
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... Nemichthys that have long curved jaws, the jaws appear to rapidly extend forward even when the larvae are still in the leptocepha- lus stage (Fig. 33B). This also occurs in serrivomerid leptocephali (Beebe and Crane 1936;Miller and Tsukamoto 2004). A major enlargement of the olfactory organ is apparent in the metamorphosing synaphobranchid in Fig. 33A. Red blood cells begin to form in at least some late stage metamorphosing leptocephali such as Derichthys serpentinus (Fig. 37B), or during the glass eel stage in Conger myriaster collected in coastal waters of southern Japan that metamor- phosed while held in an aquarium (Fig. 37A). Toward the end of metamorphosis when the young eels ...
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... lus stage (Fig. 33B). This also occurs in serrivomerid leptocephali (Beebe and Crane 1936;Miller and Tsukamoto 2004). A major enlargement of the olfactory organ is apparent in the metamorphosing synaphobranchid in Fig. 33A. Red blood cells begin to form in at least some late stage metamorphosing leptocephali such as Derichthys serpentinus (Fig. 37B), or during the glass eel stage in Conger myriaster collected in coastal waters of southern Japan that metamor- phosed while held in an aquarium (Fig. 37A). Toward the end of metamorphosis when the young eels are about to start feeding again, there is increased ossification of the skull and vertebral column, and this increased ...
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... organ is apparent in the metamorphosing synaphobranchid in Fig. 33A. Red blood cells begin to form in at least some late stage metamorphosing leptocephali such as Derichthys serpentinus (Fig. 37B), or during the glass eel stage in Conger myriaster collected in coastal waters of southern Japan that metamor- phosed while held in an aquarium (Fig. 37A). Toward the end of metamorphosis when the young eels are about to start feeding again, there is increased ossification of the skull and vertebral column, and this increased development of the skeleton generally coincides with depletion of the gelatinous support matrix (Pfeiler ...
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... et al. 1994;Chen and Tzeng 1996;Arai et al. 1997) and the Atlantic eels (e.g. Wang and Tzeng 2000) have been examined using SEM observations of increments and Sr:Ca ratio measurements. These studies suggested that there was a rapid increase in otolith increment widths during metamor- phosis that was accompanied by a decrease in Sr:Ca ratios (Fig. 38). Using these otolith charac- teristics, the timing of metamorphosis of the leptocephalus stage has been estimated in glass eels collected in coastal waters for both temperate and tropical anguillid glass eels (Marui et al. 2001;. Mean ages at metamorphosis for various anguillid species have been re- ported to range from less than a 100 ...
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... that examined different stages of larvae before and after metamorphosis. Kuroki et al. (2005) showed that the increase in increment width started during metamorphosis in the leptocephalus stage of A. marmorata, along with a decrease in Sr:Ca ratios. By comparing premetamorphic leptocephali to a metamorphosing specimen and oceanic glass eels (see Fig. 39), it was found that there was an increase in increment width in the metamorphosing leptocephalus, and an increase followed by a decrease in the oceanic glass eels. Lee and Byun (1996) found the same pattern of increment width increase in metamorphos- ing C. myriaster leptocephali, but not in premetamorphic individuals. In glass eels of ...
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... ability obtained by swimming fish at increasing speed intervals until they reach exhaustion (Fisher 2005;Fisher et al. 2005). Conger oceanicus larvae were collected during April-June at water temperatures of 14.0-24.5°C, and were separated into premetamorphic and metamorphosing leptocephali (ER-M1) and glass eels (M2-M3) as illustrated in Fig. 36 and described by Bell et al. (2003). U crit of C. oceanicus ranged from 12.0-26.8 cm s -1 for ER-M1 stage metamorphosing leptocephali and 4.1-25.0 cm s -1 for M2-M3 stage glass eels (Fig. 40C). Anguilla rostrata glass eels that recruited to the same area from January to June at temperatures of 4.0-21.0°C were considerably smaller ...
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... along the outer shelf of the East China Sea (Fig. 32) found evi- dence of spawning by many species of eels ). The two most abundant species of leptocephali were Gnathophis nystromi nystromi (Congridae) and Dysomma anguillare (Synaphobranchidae), which based on their distributions of small leptocephali were spawning at the outer edge of the shelf (Fig. 43). The exact stations at which the smallest leptocephali of the two species were caught differed slightly though, suggesting that D. anguillare was spawning a little farther out over the slope than G. nystromi nystromi. All sizes of leptocephali of the Muraenidae, Ophichthidae, and Saurenchelys (Nettastomatidae) were also abundant over ...
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... collected in slightly deeper layers than usual was in the Florida Current, which flows along the South Atlantic Bight of the US east coast. Two MOCNESS-10 surveys of mesopelagic fishes were conducted that consisted of four transects of stations across the Florida Current ( Kleckner and McCleave 1982;Miller 1995Miller , 2002a). These collections (Fig. 53) resulted in many hours of fishing effort at night (Fig. 53C) and 1,231 congrid larvae being collected, but only one leptocephalus was caught in a net that fished exclu- sively below 200 m (Fig. 53A). During the day, there was even more fishing effort at depths from 300-900 m (Fig. 53D), and 18 out of 114 total congrid leptocephali were ...
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... Florida Current, which flows along the South Atlantic Bight of the US east coast. Two MOCNESS-10 surveys of mesopelagic fishes were conducted that consisted of four transects of stations across the Florida Current ( Kleckner and McCleave 1982;Miller 1995Miller , 2002a). These collections (Fig. 53) resulted in many hours of fishing effort at night (Fig. 53C) and 1,231 congrid larvae being collected, but only one leptocephalus was caught in a net that fished exclu- sively below 200 m (Fig. 53A). During the day, there was even more fishing effort at depths from 300-900 m (Fig. 53D), and 18 out of 114 total congrid leptocephali were collected in nets that fished deeper than 300 m (Fig. 53B). ...
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... that consisted of four transects of stations across the Florida Current ( Kleckner and McCleave 1982;Miller 1995Miller , 2002a). These collections (Fig. 53) resulted in many hours of fishing effort at night (Fig. 53C) and 1,231 congrid larvae being collected, but only one leptocephalus was caught in a net that fished exclu- sively below 200 m (Fig. 53A). During the day, there was even more fishing effort at depths from 300-900 m (Fig. 53D), and 18 out of 114 total congrid leptocephali were collected in nets that fished deeper than 300 m (Fig. 53B). All but one of these were A. balearicum leptocephali (8 were undergoing metamorphosis), which suggests that their deep distributions may ...
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... McCleave 1982;Miller 1995Miller , 2002a). These collections (Fig. 53) resulted in many hours of fishing effort at night (Fig. 53C) and 1,231 congrid larvae being collected, but only one leptocephalus was caught in a net that fished exclu- sively below 200 m (Fig. 53A). During the day, there was even more fishing effort at depths from 300-900 m (Fig. 53D), and 18 out of 114 total congrid leptocephali were collected in nets that fished deeper than 300 m (Fig. 53B). All but one of these were A. balearicum leptocephali (8 were undergoing metamorphosis), which suggests that their deep distributions may have been caused by recruitment-related behavior, since larvae of one population are ...
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... at night (Fig. 53C) and 1,231 congrid larvae being collected, but only one leptocephalus was caught in a net that fished exclu- sively below 200 m (Fig. 53A). During the day, there was even more fishing effort at depths from 300-900 m (Fig. 53D), and 18 out of 114 total congrid leptocephali were collected in nets that fished deeper than 300 m (Fig. 53B). All but one of these were A. balearicum leptocephali (8 were undergoing metamorphosis), which suggests that their deep distributions may have been caused by recruitment-related behavior, since larvae of one population are thought to cross this region of the Florida Current to reach their recruitment areas (Miller 2002a). Most ...
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... which suggests that their deep distributions may have been caused by recruitment-related behavior, since larvae of one population are thought to cross this region of the Florida Current to reach their recruitment areas (Miller 2002a). Most leptocephali, however, were caught in nets that fished between the surface and various greater depths (Figs. 53A, ...
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... depths (about 300-800 m) than typically observed, but at least part of their data were collected with open nets that may have unavoidably collected some leptocephali in shallower layers than the targeted fishing depth. However, since a few leptocephali were collected at greater depths by several nets of the MOCNESS-10 in the Florida Current (Fig. 53), which should not have any contamination from other depths, it is possible that when leptocephali are approaching the continental shelves where they have the potential to recruit, they migrate vertically to greater depths, perhaps searching for the ...
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... Sulawesi Island in May (1.5 m ring net towed next to the ship), but no metamorphosing individuals were caught at the surface ( Miller et al. 2006b). Leptocephali were also frequently collected in the same way at the surface to the northwest in the Sulu Sea in both February and November ( ; Miller and Tsukamoto unpubl. data). These taxa included Fig. 53. Plots of catch rates of congrid leptocephali collected by the MOCNESS-10 opening and closing trawl in 4 transects of stations across the Florida Current that are plotted as the number of leptocephali (ind.) caught per minute each net fished, at night (A) and during daytime (B), during August 1978 and February 1979 surveys for ...
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... as leptocephali, and not as glass eels as in anguillids. A similar pattern occurs with Conger oceanicus, which is spawned offshore in the Sargasso Sea, but recruits back to temperate latitudes as leptocephali (Able and Fahay 1998;Bell et al. 2003). These Conger leptocephali have been captured while entering estuarine habitats in New Jersey ( Fig. 36; stage ER-M1) from April-June ( Wuenschel and Able 2008). Leptocephali of the common ophichthid Myrophis punctatus also enter this estuarine system (Able and Fahay 1998), and probably along the entire coastline to the south and into the Gulf of Mexico, since for example, they are also captured in tidal currents flowing into estuarine ...
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... in their spawning area (McCleave 2008). This period when increments are not deposited likely occurs during the glass eel stage because studies on metamorphosing anguilliform and elopiform leptocephali have found that otolith deposition continues during metamorphosis (Chen and Tzeng 1996;Powles et al. 2006) and wider increments are formed (Figs. 38, 39). In addition, experi- ments have shown that glass eels held at temperatures of 12°C or lower stop depositing otolith increments ( Fukuda et al. ...
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... energy until they begin their upstream migration, or hormonal changes due to inactivity, could result in minimal otolith deposition in the case of glass eels, which may be particularly adapted to conserve energy until they migrate upstream. This period of lack of deposition may correspond to what has been referred to as the "freshwater check" (Fig. 38) as mentioned previously ( Kuroki et al. 2008b;Fukuda et al. 2009). If this check is actually formed when glass eels stop migrating and wait in the substrate for a variable period of time, the fresh- water check would represent an accurate age at first recruitment if daily increments were formed prior to its formation. But due to the ...
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Citations
... Other species have a very long post-larvae stage that can last for months until they reach body lengths of >50 mm, extending their pelagic stage for weeks or months (e.g., Ophioblennius atlanticus or Mullus surmuletus) (Labelle and Nursall, 1985;Aguirre, 2000). Eels, for instance, have large elongated larvae denominated leptocephali, these larvae usually have good swimming capabilities and can present long PLD (Miller, 2009). ...
Early life stages of fish are insufficiently studied in most regions around the globe, and consequently, there is an important gap in knowledge on the life cycle of most teleosts. In the Canary Islands (Eastern Central Atlantic), most studies on ichthyoplankton communities are based on traditional net tows in open waters that provide information about early larval stages of pelagic species in the area, while nearshore benthic fish remain highly understudied. In this study, light traps were employed for the first time to assess post-larval stages of neritic fish in this archipelago. A two-year survey was carried out to collect nearshore fish larvae every 6 months at 11 localities from El Hierro, Tenerife and Lanzarote. A total of 3940 fish larvae classified into 13 orders, 28 families and 44 species were collected. These results provide a wide description of the composition of the inshore ichthyoplankton off the Canary Islands, across islands and seasons. Main environmental factors (SST, sea floor orography, oceanographic phenomena …) influencing the population dynamics of this community are discussed. Additionally, the ichthyoplankton assemblages were assessed from the intra-annual perspective, analyzing the species composition and abundances by months and seasons, and providing new insights into reproduction cycles of many common benthic fishes at shallow marine ecosystems of the islands. This study is important to further understand the life cycles of some of the most common fish species in the Canary Islands, unraveling main environmental factors that affect the success of their offspring that sustain populations.
... A similar, though less drastic, decrease in soft coral cover was also detected (from 8 to 0.3%). Such sharp decreases in coral cover have been reported in response to bleaching events worldwide 6,74,75 , followed by either an increase in turf or macroalgae (an increase from 15.3 to 25.9%, and 3.1-34.8%, respectively for the present study) 76,77 . ...
Understanding how coral reefs respond to disturbances is fundamental to assessing their resistance and resilience, particularly in the context of climate change. Due to the escalating frequency and intensity of coral bleaching events, it is essential to evaluate spatio-temporal responses of coral reef communities to disentangle the mechanisms underlying ecological changes. Here, we used benthic data collected from 59 reefs in the Red Sea over five years (2014–2019), a period that encompasses the 2015/2016 mass bleaching event. Reefs were located within three different geographic regions with different environmental settings: north (Duba; Al Wajh), central (Jeddah; Thuwal), and south (Al Lith; Farasan Banks; Farasan Islands). Coral community responses were region-specific, with communities in the south being more promptly affected than those in the northern and central regions, with hard and soft coral cover dropping drastically in several reefs from around > 40% to < 5% two years after bleaching. Coral bleaching effects were particularly evident in the decrease of cover in branching corals. Overall, we documented a shift towards a dominance of macroalgae, turf algae, and crustose coralline algae (CCA). Using remote sensing data, we analyzed sea surface temperature (SST) regimes at the study sites to infer potential drivers of changes in benthic composition. Both SST and Degree Heating Weeks (DHW) only partially aligned with the responses of benthic communities, highlighting the need for more accurate predictors of coral bleaching in the Red Sea. In times of intense coastal development along Saudi Arabia’s Red Sea coast, our study provides crucial baseline information on developments in coral reef community composition, as well as to guide decision-making, namely restoration efforts.
... Leptocephali also pose a number of challenges to researchers: (1) they are large compared to most other larval taxa, have well developed sensory systems, and are comparatively strong swimmers, and thus may avoid sampling nets more easily than other larval taxa (Castonguay and McCleave 1987): (2) leptocephali are difficult to identify to species due to the morphological similarity among species from multiple orders and the complete dissimilarity to adult forms (Miller 2009;Miller and McCleave 2007;Smith 1979); and (3) as with adult anguillids, leptocephali can be logistically challenging to study, requiring extensive vessel surveys and significant time to acquire samples. As a case in point, A. dieffenbachii leptocephali have never been identified (Jellyman 2003;Kuroki et al. 2020). ...
Freshwater eels (Anguillidae) are facing numerous anthropogenic impacts that have led to declines in abundance for nearly all species. They have a complex life history that includes obligate migration and flexible habitat use, characteristics which have generated much research interest in the family. Eels also have high cultural and economic value, further incentivizing the study of key species. We reviewed the scientific literature on anguillids from the last four decades, analyzing research trends among and within species of the genus Anguilla. We identified a shift in research focus from largely biological towards more applied management and conservation topics, an increased emphasis on migration and fish passage considerations, and a tendency towards research on glass eels and silver eels over other life stages. We also identified a significant disparity in research effort between temperate species and tropical species, with a scarcity of knowledge on the latter. Finally, we described several key knowledge gaps about community-based interactions of eels, notably their roles as predator, prey, and ecosystem connector, and highlight opportunities for early career researchers to establish research programs within the field of anguillid research.
... In addition, the elongate coracoid-basipterygium complex provided a ventral protrusion of the body wall. To reconcile these observations, we propose that viscera may have protruded from the body and along this ventral structure (Fig. 6), like in the exterilium (external) guts found in a diverse set of larval teleosts, including: conger eels (Anguilliformes, Congridae; Miller 2009Miller , 2023 Okiyama & Yamaguchi 2004;Fukui & Kuroda 2007;Suntsov 2007;Nonaka et al. 2021;Girard et al. 2023). Remarkably, at least in cusk-eels (Ophidiidae) the exterilium gut is supported by a very long descending process of the coracoid (Okiyama & Yamaguchi 2004;Suntsov 2007;Girard et al. 2023), similar to that observed in "Pegasus" volans. ...
"Pegasus" volans is a highly unusual fossil teleost fish from the celebrated Eocene Bolca Lagerstatte. The fossil, known on the basis of two specimens, has been historically assigned to seamoths (Pegasidae), then to oarfish and relatives (Lampriformes). We describe its enigmatic skeletal anatomy in detail, and provide a new genus name. "Pegasus" volans is an extremely elongate and slender animal, with long anal and dorsal fins and a very well-developed first dorsal-fin ray reminiscent to the vexillum of some modern teleost larvae. Most striking is its extreme ventral projection of the pelvic girdle (basipterygium), associated with an element of the pectoral girdle (a long process of the coracoid) and developed pelvic-fin rays. The strongly reduced abdominal region suggests that "Pegasus" volans had an external gut, once again reminiscent of those of certain larval teleosts. The unique character state combination displayed by "Pegasus" volans make it impossible to assign it to a specific subclade within perch-like spiny-rayed fishes (Percomorpha). Nevertheless, it offers a valuable perspective on the diversity of morphologies and ecological niches occupied by teleost fishes of the early Eocene Bolca fauna.
... Anguillidae, Congridae and Muraenidae) but also tenpounders (Elopidae) and tarpons (Megalopidae). The larval stage typically occurs off the reef for all of these species (Miller, 2009). ...
As global heating and other anthropogenic influences alter tropical marine environments, it is unclear how marine bird populations will be impacted and whether their current roles in tropical marine ecosystems will change. Although marine birds roost and breed on tropical islands in large numbers, the direct trophic interactions between these birds and their prey across the tropics are poorly documented. We present a first framework for evaluating the dependence on and contributions of marine birds to tropical coral reef ecosystems and use it to examine the evidence for different kinds of interaction, focusing primarily on avian diets. We found 34 publications between 1967 and 2023 that presented a total of 111 data sets with enough detail for quantitative dietary analysis of tropical marine birds. Only two bird species out of 37 (5.4%) had diets of >50% coral reef fishes and only one, the Pacific Reef Egret, appeared to depend almost entirely on reef‐based production. Marine birds are also prey for other marine organisms, but insufficient data are available for quantitative analysis. Evidence for indirect effects of birds in tropical marine environments is stronger than for direct dependence on coral reefs, particularly in relation to nutrient concentration and the fertilisation impacts of guano on corals. Dispersal of propagules (e.g. seeds, spores, invertebrate eggs) by bathing, drinking, resting or foraging birds is under‐studied and poorly documented. Although the degradation of coral reefs appears unlikely to have a significant direct impact on food availability for most marine bird populations, indirect effects involving marine birds may be disrupted by global environmental change.
... Elopomorphs are composed of the Elopiformes, Albuliformes, and Anguilliformes [19], with the later including marine and freshwater eels. All elopomorphs have leptocephalus larvae, which are a unique larval form with laterally compressed, leaf-like transparent bodies [20,21] and they undergo a remarkable metamorphosis [22,23]. During metamorphosis, they transform into a cylindrical form while there is a reduction in both the length and the depth of the body, a loss of teeth, and thickening and pigmentation of the skin [22]. ...
... All elopomorphs have leptocephalus larvae, which are a unique larval form with laterally compressed, leaf-like transparent bodies [20,21] and they undergo a remarkable metamorphosis [22,23]. During metamorphosis, they transform into a cylindrical form while there is a reduction in both the length and the depth of the body, a loss of teeth, and thickening and pigmentation of the skin [22]. Compared to flatfish, metamorphosis in elopomorphs is not well-documented or studied physiologically. ...
... Genes of cluster 1 were highly expressed at the leptocephalus stage and decreased in expression as the developmental stages progressed, while the genes of cluster 5 had the opposite expression pattern. Anguillid eel larvae are distributed in relatively low-light layers of the upper few hundred meters of the open ocean [22,72]. In contrast, the habitats of yellow eels are shallow estuarine or inland aquatic areas. ...
Background
Anguillid eels spend their larval period as leptocephalus larvae that have a unique and specialized body form with leaf-like and transparent features, and they undergo drastic metamorphosis to juvenile glass eels. Less is known about the transition of leptocephali to the glass eel stage, because it is difficult to catch the metamorphosing larvae in the open ocean. However, recent advances in rearing techniques for the Japanese eel have made it possible to study the larval metamorphosis of anguillid eels. In the present study, we investigated the dynamics of gene expression during the metamorphosis of Japanese eel leptocephali using RNA sequencing.
Results
During metamorphosis, Japanese eels were classified into 7 developmental stages according to their morphological characteristics, and RNA sequencing was used to collect gene expression data from each stage. A total of 354.8 million clean reads were generated from the body and 365.5 million from the head, after the processing of raw reads. For filtering of genes that characterize developmental stages, a classification model created by a Random Forest algorithm was built. Using the importance of explanatory variables feature obtained from the created model, we identified 46 genes selected in the body and 169 genes selected in the head that were defined as the “most characteristic genes” during eel metamorphosis. Next, network analysis and subsequently gene clustering were conducted using the most characteristic genes and their correlated genes, and then 6 clusters in the body and 5 clusters in the head were constructed. Then, the characteristics of the clusters were revealed by Gene Ontology (GO) enrichment analysis. The expression patterns and GO terms of each stage were consistent with previous observations and experiments during the larval metamorphosis of the Japanese eel.
Conclusion
Genome and transcriptome resources have been generated for metamorphosing Japanese eels. Genes that characterized metamorphosis of the Japanese eel were identified through statistical modeling by a Random Forest algorithm. The functions of these genes were consistent with previous observations and experiments during the metamorphosis of anguillid eels.
... Since 2014, the Agency has been researching the seed production techniques of Japanese eels to develop a mass-production system of glass eels. A variety of aquaculture research was conducted to learn how to spawn the artificially matured adults and rear the leptocephalus larvae of the Japanese eel (Okamura et al. 2014;Tanaka 2015), which are unusual compared to other types of fish larvae (Miller 2009), in part due to their fragile gelatinous bodies and unusual feeding preferences (Tsukamoto and Miller 2020). Various problems were encountered during Communicated by Yusuf Akhter. ...
A novel filamentous eel-leptocephalus pathogenic marine bacterium, designated strain EL160426T, was isolated from Japanese eel, Anguilla japonica, leptocephali reared at a laboratory in Mie, Japan. In experimental infection studies on eel larvae, the strain EL160426T caused massive larval mortality and was reisolated from moribund leptocephali. Characteristically, observations of infected larvae found that EL160426T forms columnar colonies on the cranial surface of larvae. The novel isolate exhibited growth at 15–30 °C, pH 7–9, and seawater concentrations of 60–150% (W/V). Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain EL160426T was most closely related to Aureispira maritima 59SAT with 97.7% sequence similarity. The whole genome sequence analysis of the strain EL160426T showed that the strain maintained a circular chromosome with a size of approximately 7.58 Mbp and the DNA G + C content was 36.2%. The major respiratory quinone was MK-7 and the predominant cellular fatty acids were 16:0, 20:4 w6c (arachidonic acid), 17:0 iso and 16:0 N alcohol. DNA relatedness between the closest phylogenetic neighbor strain EL160426T and A. maritima (JCM23207T) was less than 13%. On the basis of the polyphasic taxonomic data, the strain represents a novel species of the genus Aureispira, for which the name Aureispira anguillae sp. nov. is proposed. The type strain is EL160426T (= JCM 35024 T = TSD-286 T).
... The Anguilliformes possesses a unique larval stage termed the leptocephalus that is laterally compressed, leaf-like larva with a transparent body (Smith 1979;Miller and Tsukamoto 2004;Miller 2009). Leptocephali can drift for long distances from spawning areas to growth habitats where their juveniles and adults live because their gelatinous-like bodies are adapted to provide buoyancy (Pfeiler 1999;Tsukamoto et al. 2009). ...
... Growth rates have so far been studied only in a few species of marine eels and some anguillid species (see Miller 2009;Kuroki et al. 2014); so, the reasons for different growth rates are unknown other than for temperature effects as mentioned below. In this study, the comparison of the growth of the genera Conger and Anguilla showed that Conger grows faster than does Anguilla in the same region of the WSP (Fig. 7, Table 1). ...
Context Conger eels in temperate regions migrate offshore to reproduce in similar ways as anguillid eels do, but little is known about Conger life histories in the western South Pacific (WSP). Aims To show the larval distribution and size, species composition, and early life history of WSP conger eels. Methods Morphological and genetic species identification and otolith analysis were conducted using 71 Conger leptocephali individuals collected in five station-transects from 10 July to 3 October 2016 during the KH-16-4 cruise. Key results We found C. cinereus, C. monganius, C. verreauxi and Conger sp. 1 leptocephali. Possible spawning areas of C. cinereus and C. verreauxi were discovered, and C. verreauxi appears to migrate offshore to reproduce. Growth rates of the four conger eels were higher than those of temperate Conger species, and of Anguilla leptocephali that were collected in the WSP. Conclusions Aspects of the Conger species composition, spawning areas and larval distributions were shown. Conger leptocephali grow faster than do Anguilla leptocephali in the WSP, probably because Conger larvae have larger maximum sizes. Implications Our findings have improved understanding of the early life history of Conger species and highlighted need for further studies about life histories of Conger in the Indo-Pacific region.
... Organismal transparency is generally thought to be a mechanism for evading visual predation [1][2][3]. Several studies have assessed changes in biological transparency and have underscored the diverse influences on this trait, encompassing environmental variables [4], structural aspects [5,6], physiological factors [4,7], genetic expression [8], developmental stage [9], and more. ...
Organismal transparency constitutes a significant concern in whole-body live imaging, yet its underlying structural, genetic, and physiological foundations remain inadequately comprehended. Diverse environmental and physiological factors (multimodal factors) are recognized for their influence on organismal transparency. However, a comprehensive and integrated quantitative evaluation system for biological transparency across a broad spectrum of wavelengths is presently lacking. In this study, we have devised an evaluation system to gauge alterations in organismal transparency induced by multimodal factors, encompassing a wide range of transmittance spanning from 380 to 1000 nm, utilizing hyperspectral microscopy. Through experimentation, we have scrutinized the impact of three environmental variables (temperature, salinity, and pH) and the effect of 11 drugs treatment containing inhibitors targeting physiological processes in the ascidian Ascidiella aspersa. This particular species, known for its exceptionally transparent eggs and embryos, serves as an ideal model. We calculated bio-transparency defined as the mean transmittance ratio of visible light within the range of 400–760 nm. Our findings reveal a positive correlation between bio-transparency and temperature, while an inverse relationship is observed with salinity levels. Notably, reduced pH levels and exposure to six drugs have led to significant decreasing in bio-transparency (ranging from 4.2% to 58.6%). Principal component analysis (PCA) on the measured transmittance data classified these factors into distinct groups. This suggest diverse pathways through which opacification occurs across different spectrum regions. The outcome of our quantitative analysis of bio-transparency holds potential applicability to diverse living organisms on multiple scales. This analytical framework also contributes to a holistic comprehension of the mechanisms underlying biological transparency, which is susceptible to many environmental and physiological modalities.
... Given these observations and that preflexion (USNM 454563), flexion (USNM 465352) and postflexion (USNM 465385) larval Monomitopus were all found in and remained in or repeatedly returned to Ianniello's coil, we think these larvae are often coiled prior to settlement. While some larval fishes contort their bodies into "C" shapes (e.g., see various blackwater photographs of Callionymidae, Labridae, Synodontidae) completely overlapping or nearly overlapping coils have only been documented in the leptocephali of anguilliform families Chlopsidae, Congridae, Muraenidae, Nettastomatidae, and Ophichthidae (Miller 2009;Miller et al. 2013). Under observation, larval eels wrapped their bodies into tight spheres, several coiling one or more times around their heads (see Miller et al. 2013 figs. 2 and 3). ...
In 1985, Carter and Cohen noted that there are several yet-to-be described species of Monomitopus (Ophidiidae), including one from Hawaiʻi. Recently, blackwater divers collected a larval fish off Kona, Hawaiʻi, similar to the previously described larvae of M. kumae, but DNA sequence data from the larva does not match any of the six previously sequenced species within the genus. Within the Smithsonian Institution’s National Museum of Natural History Ichthyology Collection, we find a single unidentified adult specimen of Monomitopus collected North of Maui, Hawaiʻi in 1972 whose fin-ray and vertebral/myomere counts overlap those of the larval specimen. We describe this new Hawaiian species of Monomitopus based on larval and adult characters. Additionally, blackwater photographs of several species of Monomitopus show the larvae coiled into a tight ball, a novel behavior to be observed in cusk-eels. We describe this behavior, highlighting the importance of blackwater photography in advancing our understanding of marine larval fish biology.
