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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

Spawning-condition adult freshwater eels.(a) Female Japanese eel, Anguilla japonica, 749 mm in length with unfertilized eggs that flowed out of the genital pore after collection (dish in photo). Scale bar, 50 mm. (b) Male A. japonica (447 mm). Scale bar, 50 mm. (c) Female giant mottled eel Anguilla marmorata (1,223 mm). Scale bar, 100 mm. (d) Male A. marmorata (457 mm). Scale bar, 50 mm. (e) Comparison of the anterior part of the bodies of male A. japonica (top: 585 mm) and the A. marmorata in (d) (bottom) that were caught together in the same net, showing a greater enlargement of the eyes in A. marmorata than in A. japonica. (f) Tail part of a male A. japonica (471 mm) that was still in good condition for swimming despite its very thin body. (g) Degenerated teeth of the upper jaw of the female A. marmorata in (c).
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f1: Spawning-condition adult freshwater eels.(a) Female Japanese eel, Anguilla japonica, 749 mm in length with unfertilized eggs that flowed out of the genital pore after collection (dish in photo). Scale bar, 50 mm. (b) Male A. japonica (447 mm). Scale bar, 50 mm. (c) Female giant mottled eel Anguilla marmorata (1,223 mm). Scale bar, 100 mm. (d) Male A. marmorata (457 mm). Scale bar, 50 mm. (e) Comparison of the anterior part of the bodies of male A. japonica (top: 585 mm) and the A. marmorata in (d) (bottom) that were caught together in the same net, showing a greater enlargement of the eyes in A. marmorata than in A. japonica. (f) Tail part of a male A. japonica (471 mm) that was still in good condition for swimming despite its very thin body. (g) Degenerated teeth of the upper jaw of the female A. marmorata in (c).

Mentions: During the adult eel surveys, a total of 62 horizontal tows of large 900–3,000 m2 mouth opening scientific trawls were made mostly at night at depths of 132–766 m from June to August of 2008 and from May to June of 2009. Nine of these tows deployed at 163–303 m depth layers caught a total of 15 adult freshwater eels (Table 1, Fig. 1). A. japonica (six males and six females, Fig. 1a,b,e,f) and giant mottled eels (two males and one female, Fig. 1c–e,g) were collected at three different latitudes along the southern part of the West Mariana Ridge seamount chain (Fig. 2) in June3 and August 2008 (ref. 18), and in June 2009. These eels were caught around new moon periods of each month (4 days before to 2 days after the new moon, Fig. 3a) despite considerable sampling effort before (−10 days) and after (+6 days) the new moon (Supplementary Table S1). The timing of these collections of adults also overlapped with the collections of eggs and recently hatched preleptocephali (prefeeding-stage larvae; Fig. 3b,c).


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)

Spawning-condition adult freshwater eels.(a) Female Japanese eel, Anguilla japonica, 749 mm in length with unfertilized eggs that flowed out of the genital pore after collection (dish in photo). Scale bar, 50 mm. (b) Male A. japonica (447 mm). Scale bar, 50 mm. (c) Female giant mottled eel Anguilla marmorata (1,223 mm). Scale bar, 100 mm. (d) Male A. marmorata (457 mm). Scale bar, 50 mm. (e) Comparison of the anterior part of the bodies of male A. japonica (top: 585 mm) and the A. marmorata in (d) (bottom) that were caught together in the same net, showing a greater enlargement of the eyes in A. marmorata than in A. japonica. (f) Tail part of a male A. japonica (471 mm) that was still in good condition for swimming despite its very thin body. (g) Degenerated teeth of the upper jaw of the female A. marmorata in (c).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: Spawning-condition adult freshwater eels.(a) Female Japanese eel, Anguilla japonica, 749 mm in length with unfertilized eggs that flowed out of the genital pore after collection (dish in photo). Scale bar, 50 mm. (b) Male A. japonica (447 mm). Scale bar, 50 mm. (c) Female giant mottled eel Anguilla marmorata (1,223 mm). Scale bar, 100 mm. (d) Male A. marmorata (457 mm). Scale bar, 50 mm. (e) Comparison of the anterior part of the bodies of male A. japonica (top: 585 mm) and the A. marmorata in (d) (bottom) that were caught together in the same net, showing a greater enlargement of the eyes in A. marmorata than in A. japonica. (f) Tail part of a male A. japonica (471 mm) that was still in good condition for swimming despite its very thin body. (g) Degenerated teeth of the upper jaw of the female A. marmorata in (c).
Mentions: During the adult eel surveys, a total of 62 horizontal tows of large 900–3,000 m2 mouth opening scientific trawls were made mostly at night at depths of 132–766 m from June to August of 2008 and from May to June of 2009. Nine of these tows deployed at 163–303 m depth layers caught a total of 15 adult freshwater eels (Table 1, Fig. 1). A. japonica (six males and six females, Fig. 1a,b,e,f) and giant mottled eels (two males and one female, Fig. 1c–e,g) were collected at three different latitudes along the southern part of the West Mariana Ridge seamount chain (Fig. 2) in June3 and August 2008 (ref. 18), and in June 2009. These eels were caught around new moon periods of each month (4 days before to 2 days after the new moon, Fig. 3a) despite considerable sampling effort before (−10 days) and after (+6 days) the new moon (Supplementary Table S1). The timing of these collections of adults also overlapped with the collections of eggs and recently hatched preleptocephali (prefeeding-stage larvae; Fig. 3b,c).

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