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Katsumi Tsukamoto - One of the best experts on this subject based on the ideXlab platform.

  • Dietary supplementation with chitin hydrolysates for Anguilla japonica leptocephali
    Fisheries Science, 2020
    Co-Authors: Akihiro Okamura, Yoshiaki Yamada, Noriyuki Horie, Naomi Mikawa, Katsumi Tsukamoto
    Abstract:

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

  • evaluation of downward movements of japanese eel Anguilla japonica inhabiting brackish water areas
    Journal of Fish Biology, 2020
    Co-Authors: Ryoshiro Wakiya, Katsumi Tsukamoto, Kenzo Kaifu, Kazuhisa Azechi, Noritaka Mochioka
    Abstract:

    This study evaluated the size and age distributions and otolith microchemistry of the Japanese eel Anguilla japonica in freshwater and brackish water areas in the Aki and Tsuchikawa rivers for 1 year, and in brackish water areas in the Asahi River for 3 years to understand the movements of Japanese eels between continental habitats of different salinity after recruitment (n = 759). For all three rivers, the total length (LT ) and age distributions were consistent; yellow eels captured in the upper brackish water (Aki River: 353.5 ± 77.4 mm and 3.0 ± 0.8 years; Tsuchikawa River: 287.7 ± 87.3 mm and 3.7 ± 1.3 years; Asahi River: 418.2 ± 112.1 mm and 4.2 ± 1.7 years) were smaller and younger than not only those in the fresh water of the two rivers but also those in the lowest brackish water sampling areas (Aki River: 436.0 ± 71.6 mm and 3.8 ± 1.1 years; Tsuchikawa River: 370.9 ± 121.7 mm and 4.9 ± 2.3 years; Asahi River: 558.5 ± 85.9 mm and 5.7 ± 1.7 years). In the Asahi River, these tendencies were found throughout the 3 years. Otolith analysis indicated that the majority of the eels captured in the lowest brackish water areas had moved down from upstream. These results suggest that Japanese eels inhabiting saline water generally move from the upper estuary as they grow. The upper estuary can be an important area for the management of this species because these eels spend their early continental growth life there.

  • changes in prl gene expression during upstream movement of the japanese eel Anguilla japonica
    Zoological Science, 2019
    Co-Authors: Takashi Yada, Nobuto Fukuda, Michihisa Abe, Katsumi Tsukamoto
    Abstract:

    Changes in mRNA levels of prolactin (PRL) during upstream movement were examined in juvenile Japanese eels, Anguilla japonica. Glass eels and elvers were collected from 2007 to 2009 near the entrance of Hamana Lake, and in a small inflowing stream, the Egawa River. Quantification of mRNA was performed by real-time PCR and expressed as whole-body content. PRL mRNA levels of glass eels caught in the coastal zone and tidal area were low. Eels that moved downward in the tidal zone and migrated upstream to enter into freshwater showed increased levels of PRL mRNA. These changes suggest the importance of up-regulation of PRL gene expression in juvenile eels during their upstream movement from seawater to fresh water, particularly in relation to hyperosmoregulation.

  • development of oocytes in a post spawning japanese eel Anguilla japonica temminck schlegel in captivity
    bioRxiv, 2018
    Co-Authors: S Tanaka, Noriyuki Horie, Naomi Mikawa, Tomoko Utoh, A Okamura, Y Yamada, Huan Zhang, H P Oka, Katsumi Tsukamoto
    Abstract:

    Abstract It is generally believed that parent freshwater eels (Anguilla sp.) die soon after spawning on the assumption that eels are a semelparous (or monocyclic) fish (spawn once at the last stage of life) like Pacific salmonids. However, we observed for the first time a post-spawning female Anguilla japonica again possessed developing oocytes reaching the final maturation stage in captivity five months after the last spawning even without hormonal treatment. Here we describe information on this female about its biological characteristics including gonadal histology and endocrine profiles. The data suggest that lowering water temperature for a period of time is one of the important factors influencing spontaneous gonadal development in this specimen. We also discuss the possibility of induced multiple spawning of this species in captivity.

  • Environmental factors affecting the onset of spawning migrations of Japanese eels (Anguilla japonica) in Mikawa Bay Japan
    Environmental Biology of Fishes, 2017
    Co-Authors: Ryusuke Sudo, Akihiro Okamura, Michael J. Miller, Nobuto Fukuda, Katsumi Tsukamoto
    Abstract:

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

Jun Aoyama - One of the best experts on this subject based on the ideXlab platform.

  • demographic survey of the yellow phase japanese eel Anguilla japonica in japan
    Fisheries Science, 2014
    Co-Authors: Kazuki Yokouchi, Jun Aoyama, Katsumi Tsukamoto, Kenzo Kaifu, Yasuyuki Kaneko, Kazuo Uchida
    Abstract:

    Catch statistics and biological data of the Japanese eel Anguilla japonica from 12 river systems in nine prefectures of Japan (36°N, 140°E–31°N, 130°E) during 1999–2004 were analyzed in order to evaluate the demography of A. japonica in Japan. Significant differences in biological characteristics of 6388 eels were found among the river systems. Fishery catches of eels in all locations have declined, but the magnitudes or patterns of decline seem to be different. Of sex-identified eels, mean total lengths ± SD (mm) of females (n = 3776) and males (n = 962) were 495.6 ± 104.3 and 412.9 ± 80.7, respectively, and overall sex ratio (% female) was 79.6 %. Mean age (years) and growth rate (mm year−1) were 5.0 ± 1.9 and 96.7 ± 38.6 for females (n = 3643) and 3.6 ± 1.7 and 120.5 ± 65.4 for males (n = 907), respectively. This study highlights the demographic heterogeneity of the A. japonica among the studied river systems, which suggests that it is important to conserve a variety of habitats in multiple river systems as an inclusive management target in addition to restoration of the diversity of habitats for eels in a single river system.

  • Evaluation of the pigmentation stages and body proportions from the glass eel to yellow eel in Anguilla japonica
    Fisheries Science, 2013
    Co-Authors: Nobuto Fukuda, Jun Aoyama, Akira Shinoda, Michael J. Miller, Katsumi Tsukamoto
    Abstract:

    The pigmentation stages of Anguilla japonica were classified from the glass eel to yellow eel stage using 412 wild-caught eels from Hamana Lake and detailed developmental observations of 10 laboratory-reared eels. The sequential appearance of pigment was similar to that in A. Anguilla, except for delayed pigment formation on the nerve cord of A. japonica. The general classification of pigmentation stages (VA–VIB) in A. Anguilla was applicable to A. japonica, but the VB stage could be separated into two stages (VB1, VB2) in A. japonica. The completion of guanine deposition on the intra-abdominal membrane may be a trait to discriminate the yellow eel stage (VII) from the VIB stage. In natural conditions, wild-caught 0-age eels (n = 3,298) did not increase in size and retained a slender body form until VIA4, and then became thicker during VIB. The transition between body forms and growth may correspond to their ecological change from using passive transport in glass eels with tidal flow into rivers, to their settlement and further movements of elvers upstream. Considering this behavioral transition and pigmentation progression, it is proposed that the terms "glass eel" and "elver" could be defined as stages VA–VIA4 and VIB, respectively.

  • video observation of an eel in the Anguilla japonica spawning area along the west mariana ridge
    Fisheries Science, 2013
    Co-Authors: Katsumi Tsukamoto, Michael J. Miller, Shun Watanabe, Noritaka Mochioka, Sumihiro Koyama, Jun Aoyama
    Abstract:

    Some anguillid spawning areas are known based on collections of small larvae, but recently for the Japanese eel Anguilla japonica, adult spawners have been caught in trawls and their eggs and preleptocephali collected. The spawning area of A. japonica is located along the western side of the West Mariana Ridge, but the natural spawning behavior of this species or that of any other anguillid species has never been observed. This study reports on the first effort to observe spawning aggregations of anguillid eels that was conducted by the R/V Yokosuka using the Shinkai 6500 submersible and a Deep-Tow camera system in the A. japonica spawning area in July 2012. The submersible was deployed mostly at 200–800 m during daytime and the Deep-Tow was deployed mostly at 130–250 m during nighttime, both in multiple oblique depth tracks along linear transects. Various fishes and invertebrates were seen in the pelagic environment during day and night, but no spawning aggregations were observed. One eel was briefly recorded by a Deep-Tow camera at 20:13 on 17 July (2 days before new moon) at a depth of 179 m. The eel was recorded for <1 s as it passed in front of the camera. Its anterior body and head shape were consistent with a male A. japonica, or possibly a Derichthys serpentinus eel, but not with other mesopelagic eels. Because the tail region of the eel was not visible, species identification was not possible.

  • head shape polymorphism in japanese eels Anguilla japonica in relation to differences of somatic growth in freshwater and brackish habitats
    Journal of Fish Biology, 2013
    Co-Authors: Kenzo Kaifu, Jun Aoyama, Michael J. Miller, Kazuki Yokouchi, Katsumi Tsukamoto
    Abstract:

    The age, total length (L(T)), head shape and skull shape were investigated for 379 Japanese eels Anguilla japonica sampled in freshwater and brackish areas of the Kojima Bay-Asahi River system, Okayama, Japan, to learn about the differentiation process of head-shape polymorphism. The relative mouth width (ratio of mouth width to L(T)) of A. japonica > 400 mm L(T) collected in fresh water was significantly greater than that of fish collected in brackish water. Growth rates of mouth width and the distance from the snout to the midpoint of the eyes (the ratio of width and distance to age, respectively) were not significantly different between freshwater and brackish-water samples, whereas the somatic growth rate (the ratio of L(T) to age) of freshwater samples was significantly lower than that of brackish-water eel samples. These results suggest that the factors affecting head and somatic growth of A. japonica are not identical. According to these results and feeding patterns in each habitat reported by another study, it is suggested that somatic growth appears to play a significant role in the differentiation process of the head-shape polymorphism in A. japonica, with the slow-growing fish in fresh water becoming broad-headed and the fast-growing fish in brackish water becoming narrow-headed.

  • Diet of Japanese eels Anguilla japonica in the Kojima Bay-Asahi River system, Japan
    Environmental Biology of Fishes, 2013
    Co-Authors: Kenzo Kaifu, Jun Aoyama, Shingo Kimura, Sachie Miyazaki, Katsumi Tsukamoto
    Abstract:

    The diet of Japanese eels, Anguilla japonica , was investigated using stomach content and stable isotope analyses. Stable isotope enrichment of carbon and nitrogen (Δδ^13C and Δδ^15N) was first estimated for A. japonica by comparing the isotopic signatures (δ^13C and δ^15N) of reared eels to that of their food. The estimated isotope enrichment was then applied to the diet estimation of A. japonica in the Kojima Bay-Asahi River system, Japan, combined with conventional stomach content analysis. Stable isotope enrichment varied among tissues, from 0.2‰ to 0.8‰ for carbon and from 1.3‰ to 2.1‰ for nitrogen. Nitrogen isotope enrichment of A. japonica muscle estimated in this study was 2.1‰, which was different from the previously reported mean δ^15N enrichment of several animals of 3.4‰. These results indicate that isotope-based diet estimations for A. japonica need to use species- and tissue-specific values of isotope enrichment. In the diet analysis, stomach contents and stable isotopes revealed that (1) A. japonica appear to usually feed on a single type of prey species in each feeding session, (2) principal prey species were mud shrimp, Upogebia major , in brackish Kojima Bay and crayfish, Procambarus clarkia , in the Asahi River, (3) A. japonica in Kojima Bay primarily depend on the pelagic food web as a carbon source due to mud shrimp being filter feeders and eels in the Asahi River primarily depend on the littoral food web. Based on these results and the recently reported eel movements between Kojima Bay and the Asahi River, it appears that A. japonica can adapt to various feeding environments as opportunists, but also utilize the food resources by targeting a single type of prey species during a single feeding session.

Yoshiaki Yamada - One of the best experts on this subject based on the ideXlab platform.

  • Dietary supplementation with chitin hydrolysates for Anguilla japonica leptocephali
    Fisheries Science, 2020
    Co-Authors: Akihiro Okamura, Yoshiaki Yamada, Noriyuki Horie, Naomi Mikawa, Katsumi Tsukamoto
    Abstract:

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

  • effect of lunar periodicity on the locomotor activity of silver stage japanese eel Anguilla japonica
    Journal of Ethology, 2014
    Co-Authors: Ryusuke Sudo, Yoshiaki Yamada, Ryotaro Manabe, Katsumi Tsukamoto
    Abstract:

    Lunar periodicity has been thought to influence the onset of the spawning migration of anguillid eels. In this study, we measured daily locomotor activity of 8 silver-phase Japanese eels Anguilla japonica in outdoor tanks to examine the effect of lunar periodicity on their activity and the following seaward migration. The activity of silver eels was highest around the new moon during the early part of the experiment, which is the ordinary season of seaward migration in Japan. The observed patterns of activity may reflect the importance of the lunar cycle for the onset of the spawning migration in anguillid eels.

  • hen egg yolk and skinned krill as possible foods for rearing leptocephalus larvae of Anguilla japonica temminck schlegel
    Aquaculture Research, 2013
    Co-Authors: Akihiro Okamura, Yoshiaki Yamada, Noriyuki Horie, Naomi Mikawa, Satoru Tanaka, Hideki Kobayashi, Katsumi Tsukamoto
    Abstract:

    Usual diets for rearing leptocephalus larvae of Japanese eel Anguilla japonica include eggs of the endangered spiny dogfish Squalus acanthias (SE). We investigated the effects of alternative food materials, hen egg yolk (HEY) and exoskeleton-free (skinned) Antarctic krill (SAK), on the growth and survival of eel larvae. We found that feed comprising whole krill including exoskeleton (WAK) containing higher levels of fluoride (37.89 mg kg−1) was acutely toxic to eel larvae exposed to this alone. In contrast, extract from SAK containing lower concentrations of fluoride (4.25 mg kg−1) showed no apparent adverse effects. Growth of larvae fed a mixture of SE and SAK in a feed trial of 58 days [mean body weight (BW), 6.0 mg] was about twofold higher than that of larvae fed a mixture of SE and WAK (3.2 mg) (P < 0.01). A mixture of HEY and SAK also had some dietary benefits for eel larvae, enabling them to survive for up to 58 days and to grow significantly (mean BW, 2.4 mg), compared with their initial weight (mean BW, 0.2 mg) (P < 0.001). Although additional nutritional improvements are needed, the present results suggest that combination diet HEY and SAK may be a good alternative to SE as an effective diet for eel larvae.

  • Intestinal expression of peptide transporter 1 (PEPT1) at different life stages of Japanese eel, Anguilla japonica.
    Comparative biochemistry and physiology. Part B Biochemistry & molecular biology, 2013
    Co-Authors: Hyojin Ahn, Katsumi Tsukamoto, Yoshiaki Yamada, Akihiro Okamura, Toyoji Kaneko, Soichi Watanabe
    Abstract:

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

  • effect of water temperature on embryonic development and hatching time of the japanese eel Anguilla japonica
    Aquaculture, 2012
    Co-Authors: Hyojin Ahn, Yoshiaki Yamada, Akihiro Okamura, Noriyuki Horie, Naomi Mikawa, Satoru Tanaka, Katsumi Tsukamoto
    Abstract:

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

Akihiro Okamura - One of the best experts on this subject based on the ideXlab platform.

  • Dietary supplementation with chitin hydrolysates for Anguilla japonica leptocephali
    Fisheries Science, 2020
    Co-Authors: Akihiro Okamura, Yoshiaki Yamada, Noriyuki Horie, Naomi Mikawa, Katsumi Tsukamoto
    Abstract:

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

  • Environmental factors affecting the onset of spawning migrations of Japanese eels (Anguilla japonica) in Mikawa Bay Japan
    Environmental Biology of Fishes, 2017
    Co-Authors: Ryusuke Sudo, Akihiro Okamura, Michael J. Miller, Nobuto Fukuda, Katsumi Tsukamoto
    Abstract:

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

  • hen egg yolk and skinned krill as possible foods for rearing leptocephalus larvae of Anguilla japonica temminck schlegel
    Aquaculture Research, 2013
    Co-Authors: Akihiro Okamura, Yoshiaki Yamada, Noriyuki Horie, Naomi Mikawa, Satoru Tanaka, Hideki Kobayashi, Katsumi Tsukamoto
    Abstract:

    Usual diets for rearing leptocephalus larvae of Japanese eel Anguilla japonica include eggs of the endangered spiny dogfish Squalus acanthias (SE). We investigated the effects of alternative food materials, hen egg yolk (HEY) and exoskeleton-free (skinned) Antarctic krill (SAK), on the growth and survival of eel larvae. We found that feed comprising whole krill including exoskeleton (WAK) containing higher levels of fluoride (37.89 mg kg−1) was acutely toxic to eel larvae exposed to this alone. In contrast, extract from SAK containing lower concentrations of fluoride (4.25 mg kg−1) showed no apparent adverse effects. Growth of larvae fed a mixture of SE and SAK in a feed trial of 58 days [mean body weight (BW), 6.0 mg] was about twofold higher than that of larvae fed a mixture of SE and WAK (3.2 mg) (P < 0.01). A mixture of HEY and SAK also had some dietary benefits for eel larvae, enabling them to survive for up to 58 days and to grow significantly (mean BW, 2.4 mg), compared with their initial weight (mean BW, 0.2 mg) (P < 0.001). Although additional nutritional improvements are needed, the present results suggest that combination diet HEY and SAK may be a good alternative to SE as an effective diet for eel larvae.

  • Intestinal expression of peptide transporter 1 (PEPT1) at different life stages of Japanese eel, Anguilla japonica.
    Comparative biochemistry and physiology. Part B Biochemistry & molecular biology, 2013
    Co-Authors: Hyojin Ahn, Katsumi Tsukamoto, Yoshiaki Yamada, Akihiro Okamura, Toyoji Kaneko, Soichi Watanabe
    Abstract:

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

  • effect of water temperature on embryonic development and hatching time of the japanese eel Anguilla japonica
    Aquaculture, 2012
    Co-Authors: Hyojin Ahn, Yoshiaki Yamada, Akihiro Okamura, Noriyuki Horie, Naomi Mikawa, Satoru Tanaka, Katsumi Tsukamoto
    Abstract:

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

Michael J. Miller - One of the best experts on this subject based on the ideXlab platform.

  • Environmental factors affecting the onset of spawning migrations of Japanese eels (Anguilla japonica) in Mikawa Bay Japan
    Environmental Biology of Fishes, 2017
    Co-Authors: Ryusuke Sudo, Akihiro Okamura, Michael J. Miller, Nobuto Fukuda, Katsumi Tsukamoto
    Abstract:

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

  • Evaluation of the pigmentation stages and body proportions from the glass eel to yellow eel in Anguilla japonica
    Fisheries Science, 2013
    Co-Authors: Nobuto Fukuda, Jun Aoyama, Akira Shinoda, Michael J. Miller, Katsumi Tsukamoto
    Abstract:

    The pigmentation stages of Anguilla japonica were classified from the glass eel to yellow eel stage using 412 wild-caught eels from Hamana Lake and detailed developmental observations of 10 laboratory-reared eels. The sequential appearance of pigment was similar to that in A. Anguilla, except for delayed pigment formation on the nerve cord of A. japonica. The general classification of pigmentation stages (VA–VIB) in A. Anguilla was applicable to A. japonica, but the VB stage could be separated into two stages (VB1, VB2) in A. japonica. The completion of guanine deposition on the intra-abdominal membrane may be a trait to discriminate the yellow eel stage (VII) from the VIB stage. In natural conditions, wild-caught 0-age eels (n = 3,298) did not increase in size and retained a slender body form until VIA4, and then became thicker during VIB. The transition between body forms and growth may correspond to their ecological change from using passive transport in glass eels with tidal flow into rivers, to their settlement and further movements of elvers upstream. Considering this behavioral transition and pigmentation progression, it is proposed that the terms "glass eel" and "elver" could be defined as stages VA–VIA4 and VIB, respectively.

  • video observation of an eel in the Anguilla japonica spawning area along the west mariana ridge
    Fisheries Science, 2013
    Co-Authors: Katsumi Tsukamoto, Michael J. Miller, Shun Watanabe, Noritaka Mochioka, Sumihiro Koyama, Jun Aoyama
    Abstract:

    Some anguillid spawning areas are known based on collections of small larvae, but recently for the Japanese eel Anguilla japonica, adult spawners have been caught in trawls and their eggs and preleptocephali collected. The spawning area of A. japonica is located along the western side of the West Mariana Ridge, but the natural spawning behavior of this species or that of any other anguillid species has never been observed. This study reports on the first effort to observe spawning aggregations of anguillid eels that was conducted by the R/V Yokosuka using the Shinkai 6500 submersible and a Deep-Tow camera system in the A. japonica spawning area in July 2012. The submersible was deployed mostly at 200–800 m during daytime and the Deep-Tow was deployed mostly at 130–250 m during nighttime, both in multiple oblique depth tracks along linear transects. Various fishes and invertebrates were seen in the pelagic environment during day and night, but no spawning aggregations were observed. One eel was briefly recorded by a Deep-Tow camera at 20:13 on 17 July (2 days before new moon) at a depth of 179 m. The eel was recorded for <1 s as it passed in front of the camera. Its anterior body and head shape were consistent with a male A. japonica, or possibly a Derichthys serpentinus eel, but not with other mesopelagic eels. Because the tail region of the eel was not visible, species identification was not possible.

  • head shape polymorphism in japanese eels Anguilla japonica in relation to differences of somatic growth in freshwater and brackish habitats
    Journal of Fish Biology, 2013
    Co-Authors: Kenzo Kaifu, Jun Aoyama, Michael J. Miller, Kazuki Yokouchi, Katsumi Tsukamoto
    Abstract:

    The age, total length (L(T)), head shape and skull shape were investigated for 379 Japanese eels Anguilla japonica sampled in freshwater and brackish areas of the Kojima Bay-Asahi River system, Okayama, Japan, to learn about the differentiation process of head-shape polymorphism. The relative mouth width (ratio of mouth width to L(T)) of A. japonica > 400 mm L(T) collected in fresh water was significantly greater than that of fish collected in brackish water. Growth rates of mouth width and the distance from the snout to the midpoint of the eyes (the ratio of width and distance to age, respectively) were not significantly different between freshwater and brackish-water samples, whereas the somatic growth rate (the ratio of L(T) to age) of freshwater samples was significantly lower than that of brackish-water eel samples. These results suggest that the factors affecting head and somatic growth of A. japonica are not identical. According to these results and feeding patterns in each habitat reported by another study, it is suggested that somatic growth appears to play a significant role in the differentiation process of the head-shape polymorphism in A. japonica, with the slow-growing fish in fresh water becoming broad-headed and the fast-growing fish in brackish water becoming narrow-headed.

  • Genetic identification and morphology of naturally spawned eggs of the Japanese eel Anguilla japonica collected in the western North Pacific
    Fisheries Science, 2011
    Co-Authors: Tatsuki Yoshinaga, Jun Aoyama, Shingo Kimura, Akira Shinoda, Michael J. Miller, Shun Watanabe, Kazuki Yokouchi, Tsuguo Otake, Machiko Oya, Sachie Miyazaki
    Abstract:

    Eggs of the Japanese eel Anguilla japonica collected in the western North Pacific were identified by onboard species-specific polymerase chain reaction (PCR) and DNA nucleotide sequencing after the cruise. Fish eggs of various species were collected by large plankton net tows at 12 stations along the southern part of the West Mariana Ridge on 19–25 May 2009. A total of 43 fish eggs were distinguished morphologically as possibly being of A. japonica . Thirty-one of those were analyzed by PCR, which included 15 eggs collected at 12°50–55′N, 141°15–20′E (in 5 tows) that showed positive results. The 16S ribosomal RNA (rRNA) gene sequences of eggs determined after the cruise indicated that 31 A. japonica eggs had been collected. The remaining eggs were of mesopelagic eel species (Serrivomeridae and Derichthyidae), or unidentified species. The morphological characteristics of the A. japonica eggs were consistent with those of artificially spawned eggs, except they had a slightly larger diameter. The egg diameter range did not overlap with those of mesopelagic eels of the Serrivomeridae, which often spawn in the same area as A. japonica . These results suggest that egg diameter and embryo shape can be used to morphologically identify naturally spawned A. japonica eggs.