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Oceanic spawning ecology of freshwater eels in the western North Pacific.

Tsukamoto K, Chow S, Otake T, Kurogi H, Mochioka N, Miller MJ, Aoyama J, Kimura S, Watanabe S, Yoshinaga T, Shinoda A, Kuroki M, Oya M, Watanabe T, Hata K, Ijiri S, Kazeto Y, Nomura K, Tanaka H - Nat Commun (2011)

Bottom Line: The first collection of Japanese eel eggs near the West Mariana Ridge where adults and newly hatched larvae were also caught shows that spawning occurs during new moon periods throughout the spawning season.The depths where adults and newly hatched larvae were captured indicate that spawning occurs in shallower layers of 150-200 m and not at great depths.This type of spawning may reduce predation and facilitate reproductive success.

View Article: PubMed Central - PubMed

Affiliation: Department of Marine Bioscience, Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8564, Japan. ktpc@aori.u-tokyo.ac.jp

ABSTRACT
The natural reproductive ecology of freshwater eels remained a mystery even after some of their offshore spawning areas were discovered approximately 100 years ago. In this study, we investigate the spawning ecology of freshwater eels for the first time using collections of eggs, larvae and spawning-condition adults of two species in their shared spawning area in the Pacific. Ovaries of female Japanese eel and giant mottled eel adults were polycyclic, suggesting that freshwater eels can spawn more than once during a spawning season. The first collection of Japanese eel eggs near the West Mariana Ridge where adults and newly hatched larvae were also caught shows that spawning occurs during new moon periods throughout the spawning season. The depths where adults and newly hatched larvae were captured indicate that spawning occurs in shallower layers of 150-200 m and not at great depths. This type of spawning may reduce predation and facilitate reproductive success.

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Related in: MedlinePlus

Eel collection sites.Preleptocephalus catch locations of the Japanese eel, Anguilla japonica, in five different years (largest circles) and of the giant mottled eel, Anguilla marmorata, in 2 years (medium sized pink circles) are shown in relation to where adult eels were collected (three yellow ovals, Fig. 2), and the location of the grid of stations (blue rectangle) where 31 A. japonica eggs were collected (red square) just south of the salinity front (dotted red line) that crossed the southern end of the seamount chain in May 2009. The salinity front forms from higher tropical rainfall in the south, and its position appears to affect the latitude of spawning by adult eels23132. A. japonica preleptocephalus catches are shown for 2005 (ref. 36; red circles), 2007 (blue circles), 2008 (green circles Leg 1, yellow circles Leg 2) and 2009 (KH-09-02, white circles) with large circles containing the number of preleptocephali collected, and small circles of the same colour showing no-catch stations during each of those cruises. Small circles of other colours were stations of other cruises in different months or years that did not collect preleptocephali (2005-Leg 4: orange, 2006-Leg 3: purple, 2006-Leg 5: light purple, 2007-Leg 3: light blue, 2009-KH-09-1: grey). Stations in which 29 preleptocephali of A. marmorata, were collected in 2006 (darker pink) and 2007 (lighter pink) are also shown, and two other A. marmorata preleptocephali were collected at 13.5°N, 137°E in August 2006 (ref. 15). Bathymetric depth is shown by colour, with shallower depths <4,000 m in yellow and brown and deeper depths in blue. Three shallow seamounts10 are shown with black triangles. Black scale bar, 50 km.
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f5: Eel collection sites.Preleptocephalus catch locations of the Japanese eel, Anguilla japonica, in five different years (largest circles) and of the giant mottled eel, Anguilla marmorata, in 2 years (medium sized pink circles) are shown in relation to where adult eels were collected (three yellow ovals, Fig. 2), and the location of the grid of stations (blue rectangle) where 31 A. japonica eggs were collected (red square) just south of the salinity front (dotted red line) that crossed the southern end of the seamount chain in May 2009. The salinity front forms from higher tropical rainfall in the south, and its position appears to affect the latitude of spawning by adult eels23132. A. japonica preleptocephalus catches are shown for 2005 (ref. 36; red circles), 2007 (blue circles), 2008 (green circles Leg 1, yellow circles Leg 2) and 2009 (KH-09-02, white circles) with large circles containing the number of preleptocephali collected, and small circles of the same colour showing no-catch stations during each of those cruises. Small circles of other colours were stations of other cruises in different months or years that did not collect preleptocephali (2005-Leg 4: orange, 2006-Leg 3: purple, 2006-Leg 5: light purple, 2007-Leg 3: light blue, 2009-KH-09-1: grey). Stations in which 29 preleptocephali of A. marmorata, were collected in 2006 (darker pink) and 2007 (lighter pink) are also shown, and two other A. marmorata preleptocephali were collected at 13.5°N, 137°E in August 2006 (ref. 15). Bathymetric depth is shown by colour, with shallower depths <4,000 m in yellow and brown and deeper depths in blue. Three shallow seamounts10 are shown with black triangles. Black scale bar, 50 km.

Mentions: The most unquestionable evidence of a spawning event by A. japonica near the West Mariana Ridge during the new moon was found in May 2009 when the first anguillid eel eggs of any species were found (Fig. 4). Thirty-one eggs of A. japonica were collected in five tows at three stations in a grid of 25 stations centred around the first egg collection site (Fig. 5, Supplementary Fig. S2). The eggs were collected just south of the salinity front that was hypothesized to affect the latitude of spawning23132, and in May 2009 the front crossed the seamount chain at around 13°N (Fig. 5). The eggs that had been fertilized and were developing (termed 'embryos'; Fig. 4) were identified by morphology as possibly being A. japonica eggs because of their similarity with artificially fertilized eggs33, and were genetically confirmed to be A. japonica onboard the R/V Hakuho Maru within a few hours of the first egg collection using a real-time PCR system34 that is designed to distinguish samples of Japanese eels from those of other similar species of eels onboard.


Oceanic spawning ecology of freshwater eels in the western North Pacific.

Tsukamoto K, Chow S, Otake T, Kurogi H, Mochioka N, Miller MJ, Aoyama J, Kimura S, Watanabe S, Yoshinaga T, Shinoda A, Kuroki M, Oya M, Watanabe T, Hata K, Ijiri S, Kazeto Y, Nomura K, Tanaka H - Nat Commun (2011)

Eel collection sites.Preleptocephalus catch locations of the Japanese eel, Anguilla japonica, in five different years (largest circles) and of the giant mottled eel, Anguilla marmorata, in 2 years (medium sized pink circles) are shown in relation to where adult eels were collected (three yellow ovals, Fig. 2), and the location of the grid of stations (blue rectangle) where 31 A. japonica eggs were collected (red square) just south of the salinity front (dotted red line) that crossed the southern end of the seamount chain in May 2009. The salinity front forms from higher tropical rainfall in the south, and its position appears to affect the latitude of spawning by adult eels23132. A. japonica preleptocephalus catches are shown for 2005 (ref. 36; red circles), 2007 (blue circles), 2008 (green circles Leg 1, yellow circles Leg 2) and 2009 (KH-09-02, white circles) with large circles containing the number of preleptocephali collected, and small circles of the same colour showing no-catch stations during each of those cruises. Small circles of other colours were stations of other cruises in different months or years that did not collect preleptocephali (2005-Leg 4: orange, 2006-Leg 3: purple, 2006-Leg 5: light purple, 2007-Leg 3: light blue, 2009-KH-09-1: grey). Stations in which 29 preleptocephali of A. marmorata, were collected in 2006 (darker pink) and 2007 (lighter pink) are also shown, and two other A. marmorata preleptocephali were collected at 13.5°N, 137°E in August 2006 (ref. 15). Bathymetric depth is shown by colour, with shallower depths <4,000 m in yellow and brown and deeper depths in blue. Three shallow seamounts10 are shown with black triangles. Black scale bar, 50 km.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3105336&req=5

f5: Eel collection sites.Preleptocephalus catch locations of the Japanese eel, Anguilla japonica, in five different years (largest circles) and of the giant mottled eel, Anguilla marmorata, in 2 years (medium sized pink circles) are shown in relation to where adult eels were collected (three yellow ovals, Fig. 2), and the location of the grid of stations (blue rectangle) where 31 A. japonica eggs were collected (red square) just south of the salinity front (dotted red line) that crossed the southern end of the seamount chain in May 2009. The salinity front forms from higher tropical rainfall in the south, and its position appears to affect the latitude of spawning by adult eels23132. A. japonica preleptocephalus catches are shown for 2005 (ref. 36; red circles), 2007 (blue circles), 2008 (green circles Leg 1, yellow circles Leg 2) and 2009 (KH-09-02, white circles) with large circles containing the number of preleptocephali collected, and small circles of the same colour showing no-catch stations during each of those cruises. Small circles of other colours were stations of other cruises in different months or years that did not collect preleptocephali (2005-Leg 4: orange, 2006-Leg 3: purple, 2006-Leg 5: light purple, 2007-Leg 3: light blue, 2009-KH-09-1: grey). Stations in which 29 preleptocephali of A. marmorata, were collected in 2006 (darker pink) and 2007 (lighter pink) are also shown, and two other A. marmorata preleptocephali were collected at 13.5°N, 137°E in August 2006 (ref. 15). Bathymetric depth is shown by colour, with shallower depths <4,000 m in yellow and brown and deeper depths in blue. Three shallow seamounts10 are shown with black triangles. Black scale bar, 50 km.
Mentions: The most unquestionable evidence of a spawning event by A. japonica near the West Mariana Ridge during the new moon was found in May 2009 when the first anguillid eel eggs of any species were found (Fig. 4). Thirty-one eggs of A. japonica were collected in five tows at three stations in a grid of 25 stations centred around the first egg collection site (Fig. 5, Supplementary Fig. S2). The eggs were collected just south of the salinity front that was hypothesized to affect the latitude of spawning23132, and in May 2009 the front crossed the seamount chain at around 13°N (Fig. 5). The eggs that had been fertilized and were developing (termed 'embryos'; Fig. 4) were identified by morphology as possibly being A. japonica eggs because of their similarity with artificially fertilized eggs33, and were genetically confirmed to be A. japonica onboard the R/V Hakuho Maru within a few hours of the first egg collection using a real-time PCR system34 that is designed to distinguish samples of Japanese eels from those of other similar species of eels onboard.

Bottom Line: The first collection of Japanese eel eggs near the West Mariana Ridge where adults and newly hatched larvae were also caught shows that spawning occurs during new moon periods throughout the spawning season.The depths where adults and newly hatched larvae were captured indicate that spawning occurs in shallower layers of 150-200 m and not at great depths.This type of spawning may reduce predation and facilitate reproductive success.

View Article: PubMed Central - PubMed

Affiliation: Department of Marine Bioscience, Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8564, Japan. ktpc@aori.u-tokyo.ac.jp

ABSTRACT
The natural reproductive ecology of freshwater eels remained a mystery even after some of their offshore spawning areas were discovered approximately 100 years ago. In this study, we investigate the spawning ecology of freshwater eels for the first time using collections of eggs, larvae and spawning-condition adults of two species in their shared spawning area in the Pacific. Ovaries of female Japanese eel and giant mottled eel adults were polycyclic, suggesting that freshwater eels can spawn more than once during a spawning season. The first collection of Japanese eel eggs near the West Mariana Ridge where adults and newly hatched larvae were also caught shows that spawning occurs during new moon periods throughout the spawning season. The depths where adults and newly hatched larvae were captured indicate that spawning occurs in shallower layers of 150-200 m and not at great depths. This type of spawning may reduce predation and facilitate reproductive success.

Show MeSH
Related in: MedlinePlus