Vol. 58, 2019
Age, Growth, and Sex Ratios of the
Giant Mottled eel, Anguilla marmorata,
in Freshwater Habitats Near Their Northern Geographic Limit: a
Comparison to Tropical Regions
Wakiya1,*, Hikaru Itakura2, and Kenzo Kaifu3
and Development Initiative, Chuo University, 1-13-27 Kasuga, Bunkyo-ku,
Tokyo 112-8551, Japan. *Correspondence: Tel: +818056758725. E-mail:
2Graduate School of Sciences, Kobe University, 1-1
Rokkoudaichou, Nadaku, Kobe, Hyogo 657-8501 Japan, E-mail:
3Faculty of Law, Chuo University, 742-1 Higashinakano,
Hachioji-shi, Tokyo 192-0393 Japan, E-mail: firstname.lastname@example.org
Received 19 March 2019 / Accepted 18
Communicated by Benny K.K. Chan
To understand the latitudinal
difference in the basic ecology of the giant mottled eel Anguilla marmorata, we measured
their age, growth, and sex ratios in freshwater areas of Amami-Oshima
Island, Japan (28.223°N–28.332°N and 129.329°E–129.439°E), near the
northern geographic limit of its range and compared these biological
characteristics with those observed in the tropical regions of
Indonesia. A total of 109 A.
marmorata were captured from three rivers on Amami-Oshima
Island. The total length (TL) and age of sampled individuals varied
across an order of magnitude (TL range: 119–1320 mm, mean: 385.5 ±
172.6; age range: 3–30 years, mean: 12.8 ± 4.9 years). Both TL and age
did not differ among rivers. Male A.
marmorata accounted for 88.5% of sexually differentiated
individuals, a finding that was contrary to previous results for males
living in Indonesian watersheds where males were only found in small
rivers and areas close to estuaries. Moreover, we found no males larger
than 700 mm in TL and few males that were older than 20 years. The
growth rates of male A. marmorata were
significantly lower than females, and growth rates of sexually
undifferentiated fish were significantly less than males. The mean
growth rate of all individuals was 25.9 ± 6.6 mm/y, which was
considerably less than what has been found at lower latitudes,
suggesting that growth differences occur along a latitudinal cline.
Key words: Age, Anguilla marmorata, Freshwater,
Growth rate, Sex ratio.
Citation: Wakiya R, Itakura H, Kaifu K.
2019. Age, growth, and sex ratios of the giant mottled eel, Anguilla
marmorata, in freshwater habitats near their northern geographic limit:
a comparison to tropical regions. Zool Stud 58:0gg. doi:-.