Vol. 58, 2019
(update: 2019.09.23; 11.12)
Age, Growth, and Sex Ratios of the Giant Mottled eel, Anguilla marmorata, in Freshwater Habitats Near Its Northern Geographic Limit: A Comparison to Tropical Regions
Ryoshiro
Wakiya1,*, Hikaru Itakura2, and Kenzo Kaifu3
doi:10.6620/ZS.2019.58-34
1Research
and Development Initiative, Chuo University, 1-13-27 Kasuga, Bunkyo-ku,
Tokyo 112-8551, Japan. *Correspondence: Tel: +818056758725. E-mail:
ryoshiro.wakiya@gmail.com
2Graduate School of Sciences, Kobe University, 1-1
Rokkoudaichou, Nadaku, Kobe, Hyogo 657-8501 Japan, E-mail:
itakurahikaru@gmail.com
3Faculty of Law, Chuo University, 742-1 Higashinakano,
Hachioji-shi, Tokyo 192-0393 Japan, E-mail: kaifu@tamacc.chuo-u.ac.jp
Received 19 March 2019 / Accepted 18
September 2019
Communicated by Benny K.K. Chan
To understand the latitudinal difference in the basic ecology of the giant mottled eel Anguilla marmorata,
we measured its 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). Neither TL nor age differed among
rivers. Male A. marmorata
accounted for 88.5% of sexually differentiated individuals, which it
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 those of females, and growth rates of
sexually undifferentiated fish were significantly less than those of
males. The mean growth rate of all individuals was 25.9 ± 6.6 mm/y,
which is considerably lower 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 its
northern geographic limit: a comparison to tropical regions. Zool Stud 58:34. doi:10.6620/ZS.2019.58-34.
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