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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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Naturally spawned eggs of the Japanese eel Anguilla japonica.(a) Early-mid embryonic stage egg collected on 22 May 2009 near the West Mariana Ridge in the western North Pacific. (b) Late embryonic stage egg just before hatching collected on 23 May 2009 in the same area (Supplementary Fig. S2). Scale bars, 0.5 mm.
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f4: Naturally spawned eggs of the Japanese eel Anguilla japonica.(a) Early-mid embryonic stage egg collected on 22 May 2009 near the West Mariana Ridge in the western North Pacific. (b) Late embryonic stage egg just before hatching collected on 23 May 2009 in the same area (Supplementary Fig. S2). Scale bars, 0.5 mm.

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)

Naturally spawned eggs of the Japanese eel Anguilla japonica.(a) Early-mid embryonic stage egg collected on 22 May 2009 near the West Mariana Ridge in the western North Pacific. (b) Late embryonic stage egg just before hatching collected on 23 May 2009 in the same area (Supplementary Fig. S2). Scale bars, 0.5 mm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: Naturally spawned eggs of the Japanese eel Anguilla japonica.(a) Early-mid embryonic stage egg collected on 22 May 2009 near the West Mariana Ridge in the western North Pacific. (b) Late embryonic stage egg just before hatching collected on 23 May 2009 in the same area (Supplementary Fig. S2). Scale bars, 0.5 mm.
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