Zoological Studies

Vol. 58, 2019

(update: 2019.09.23)

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

Ryoshiro Wakiya1,*, Hikaru Itakura2, and Kenzo Kaifu3


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 their age, growth, and sex ratios in freshwater areas of Amami-Oshima Island, Japan (28.223N–28.332N and 129.329E–129.439E), 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:-.