Zoological Studies

Vol. 51 No. 1, 2012

Species Composition and Seasonal Occurrence of Recruiting Glass Eels (Anguilla spp.) in the Hsiukuluan River, Eastern Taiwan

Nico Jose Leander1, Kang-Ning Shen1, Rung-Tsung Chen3, and Wann-Nian Tzeng1,2,4,*

1Institute of Fisheries Science, National Taiwan Univ., Taipei 106, Taiwan
2Department of Life Science, College of Life Science, National Taiwan Univ., Taipei 106, Taiwan
3Endemic Species Research Institute, Chichi, Nantou 552, Taiwan
4Department of Environmental Biology and Fisheries Science, National Taiwan Ocean Univ., Keelung 202, Taiwan

Nico Jose Leander, Kang-Ning Shen, Rung-Tsung Chen, and Wann-Nian Tzeng (2012) There are 16 species and 3 subspecies of freshwater eel (Anguilla spp.) found in the world. Among them, 4 species, A. japonica, A. marmorata, A. bicolor pacifica, and A. celebesensis were reported from Taiwan. Anguilla japonica is an important aquaculture species and is abundant on the west coast of Taiwan, while the rest are tropical species and are more abundant on the east coast. In addition, A. celebesensis, which was identified in Taiwan in the past, appears to be the new species A. luzonensis (A. huangi) described from northern Luzon, the Philippines. To clarify these issues, the species composition, relative abundances, and seasonal occurrences of anguillid eels on the east coast of Taiwan were investigated based on 1004 glass eel specimens collected from the estuary of the Hsiukuluan River, eastern Taiwan in 2005-2009. Eel species were identified using morphological characters such as caudal fin pigmentation patterns, the position of the origin of the dorsal fin, and body proportions. The reliability of the morphological method for species identification was checked by a DNA analysis. Anguilla marmorata was the most abundant eel species in the Hsiukuluan River, making up 98.4% of the total catch, while there were very few A. bicolor pacifica (1.6%) and A. japonica (< 1%). Anguilla marmorata recruited mainly to the estuary during spring to summer but was found year-round, while A. bicolor pacifica recruited mainly during autumn. Results of the DNA analysis did not support the occurrence of A. luzonensis and/or A. celebesensis based on differences in the distance between the origin of the dorsal and anal fins as a percent of total length (ADL/%TL). Anguilla celebesensis, which was identified in the past, was not found in this study and might just be the newly described eel species, A. luzonensis, or just a phenotypic variation of A. marmorat . Differences in abundances and geographic distributions of these eel species were explained by their temperature preferences, species origins, and current systems in the coastal waters of Taiwan.

Key words: Japanese eel, Giant mottled eel, Indonesian shortfin eel, Glass eels, Temporal and spatial distribution.

*Correspondence: Tel: 886-2-33662887. Fax: 886-2-23639570. E-mail:wnt@ntu.edu.tw