Limits...
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.

Show MeSH
Depth distribution of Anguilla japonica preleptocephali in relation to environmental conditions.The changes of each environmental parameter are plotted by depth from the ocean surface, and the number of preleptocephali that were collected at each depth stratum (65, 135, 163, 188, 265 and 425 m) is shown by purple bars (no catch tows are shown by zeros). The presence of the thermocline (shaded area between dotted lines) can be seen as the sudden change in water temperature (dark blue line) with depth. The large increase in chlorophyll concentration (black line) at around 150 m also occurred just above the top of the thermocline. Sigma-t (orange line) is a measure of water density that is calculated from both salinity (light blue line) and temperature. These data were collected on 23 May 2009 at the green circle in Supplementary Figure S2 in the grid of 25 stations at the southern part of the West Mariana Ridge where the intensive survey for eel eggs and preleptocephali was made during 22–25 May 2009.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3105336&req=5

f6: Depth distribution of Anguilla japonica preleptocephali in relation to environmental conditions.The changes of each environmental parameter are plotted by depth from the ocean surface, and the number of preleptocephali that were collected at each depth stratum (65, 135, 163, 188, 265 and 425 m) is shown by purple bars (no catch tows are shown by zeros). The presence of the thermocline (shaded area between dotted lines) can be seen as the sudden change in water temperature (dark blue line) with depth. The large increase in chlorophyll concentration (black line) at around 150 m also occurred just above the top of the thermocline. Sigma-t (orange line) is a measure of water density that is calculated from both salinity (light blue line) and temperature. These data were collected on 23 May 2009 at the green circle in Supplementary Figure S2 in the grid of 25 stations at the southern part of the West Mariana Ridge where the intensive survey for eel eggs and preleptocephali was made during 22–25 May 2009.

Mentions: Eggs were collected in a narrow time window (Fig. 3b) with similar developmental stages being obtained for two consecutive days (22–23 May). They were all at the embryonic stage, but ranged from early embryonic (Fig. 4a) to late embryonic stage just before hatching (Fig. 4b). They had egg yolk and one large oil droplet, and the egg capsule diameters were 1.49–1.71 mm (1.61±0.07 mm, mean±s.d.). These eggs were larger than those obtained from artificially spawned A. japonica females33 (1.3–1.6 mm, IRAGO Institute, personal communication). On the basis of studies of artificially fertilized eggs that developed at different temperatures in the laboratory3335 and the temperatures just below the top of thermocline in the present study (Fig. 6), the collected eggs were likely spawned on the night of 20–21 May, approximately 3.5 days before the new moon (Fig. 3b).


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)

Depth distribution of Anguilla japonica preleptocephali in relation to environmental conditions.The changes of each environmental parameter are plotted by depth from the ocean surface, and the number of preleptocephali that were collected at each depth stratum (65, 135, 163, 188, 265 and 425 m) is shown by purple bars (no catch tows are shown by zeros). The presence of the thermocline (shaded area between dotted lines) can be seen as the sudden change in water temperature (dark blue line) with depth. The large increase in chlorophyll concentration (black line) at around 150 m also occurred just above the top of the thermocline. Sigma-t (orange line) is a measure of water density that is calculated from both salinity (light blue line) and temperature. These data were collected on 23 May 2009 at the green circle in Supplementary Figure S2 in the grid of 25 stations at the southern part of the West Mariana Ridge where the intensive survey for eel eggs and preleptocephali was made during 22–25 May 2009.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f6: Depth distribution of Anguilla japonica preleptocephali in relation to environmental conditions.The changes of each environmental parameter are plotted by depth from the ocean surface, and the number of preleptocephali that were collected at each depth stratum (65, 135, 163, 188, 265 and 425 m) is shown by purple bars (no catch tows are shown by zeros). The presence of the thermocline (shaded area between dotted lines) can be seen as the sudden change in water temperature (dark blue line) with depth. The large increase in chlorophyll concentration (black line) at around 150 m also occurred just above the top of the thermocline. Sigma-t (orange line) is a measure of water density that is calculated from both salinity (light blue line) and temperature. These data were collected on 23 May 2009 at the green circle in Supplementary Figure S2 in the grid of 25 stations at the southern part of the West Mariana Ridge where the intensive survey for eel eggs and preleptocephali was made during 22–25 May 2009.
Mentions: Eggs were collected in a narrow time window (Fig. 3b) with similar developmental stages being obtained for two consecutive days (22–23 May). They were all at the embryonic stage, but ranged from early embryonic (Fig. 4a) to late embryonic stage just before hatching (Fig. 4b). They had egg yolk and one large oil droplet, and the egg capsule diameters were 1.49–1.71 mm (1.61±0.07 mm, mean±s.d.). These eggs were larger than those obtained from artificially spawned A. japonica females33 (1.3–1.6 mm, IRAGO Institute, personal communication). On the basis of studies of artificially fertilized eggs that developed at different temperatures in the laboratory3335 and the temperatures just below the top of thermocline in the present study (Fig. 6), the collected eggs were likely spawned on the night of 20–21 May, approximately 3.5 days before the new moon (Fig. 3b).

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