Zoological Studies

Vol. 53, 2014

Occurrence and biological characteristics of glass eels of the Japanese eel Anguilla japonica at the Cagayan River of Luzon Island, Philippines in 2009

Tatsuki Yoshinaga1*, Jun Aoyama2, Akira Shinoda3, Shun Watanabe2,5, Rhodora V Azanza4 and Katsumi Tsukamoto2,5

1School of Marine Biosciences, Kitasato University, Kanagawa 252-0373, Japan
2Atmosphere and Ocean Research Institute, The University of Tokyo, Chiba 277-8564, Japan
3Department of Biology, Tokyo Medical University, Tokyo 160-8402, Japan
4The Marine Science Institute, University of the Philippines, Quezon City 1101, Philippines
5Present address: College of Bioresource Sciences, Nihon University, Kanagawa 252-0880, Japan

Abstract
Background: The Japanese eel Anguilla japonica spawns in the North Equatorial Current in the Philippine Sea and their larvae are transported to their freshwater growth habitats in East Asia. Here we report the occurrence and biological characteristics of glass eels of A. japonica that were collected on northern Luzon Island of the Philippines, the southern limit of the distribution range of this species. Anguillid glass eels recruiting to the Cagayan River estuary in January and February 2009 were collected and identified using their morphological and genetic characteristics.
Results:
Among the 767 specimens, 52 glass eels collected in January were found to be A. japonica, while the remaining were tropical anguillid species. Age estimation revealed that the glass eels of A. japonica from northern Luzon Island were 147.2 21.3 days old (mean sd) with a range between 111 and 185. The hatch dates of these A. japonica suggested that they were derived from at least four spawning events in the 2008 spawning season.
Conclusions: Despite the increasing demand on the glass eels for aquaculture in the area where the five anguillid species simultaneously recruit, abundance of each species is yet unknown and investigations will be important for the protection of stock of the anguillids.

Key words: Anguilla japonica; Cagayan River; Japanese eel; Philippines.

*Correspondence: E-mail: yosinaga@kitasato-u.ac.jp