Zoological Studies

Vol. 49 No. 4, 2010

The Migratory Environmental History of Freshwater Resident Flathead Mullet Mugil cephalus L. in the Tanshui River, Northern Taiwan

Chia-Hui Wang1, Chih-Chieh Hsu1,2, Chih-Wei Chang3,4, Chen-Feng You1, and Wann-Nian Tzeng2,*

1Earth Dynamic System Research Center, National Cheng Kung University, 1 University Rd., Tainan 701, Taiwan
2Institute of Fisheries Science, National Taiwan University, 1 Roosevelt Rd., Sec. 4, Taipei 106, Taiwan
3National Museum of Marine Biology and Aquarium, 2 Houwan Rd., Checheng, Pintung 944, Taiwan
4Institute of Marine Biodiversity and Evolution, National Donghwa University, 1 Da-Hsueh Rd., Sec. 2, Shoufeng, Hualien 974, Taiwan

Chia-Hui Wang, Chih-Chieh Hsu, Chih-Wei Chang, Chen-Feng You, and Wann-Nian Tzeng (2010) The diversity of the migratory environmental history of freshwater resident flathead mullet Mugil cephalus was examined by analyzing the otolith elemental composition of mullet (n = 31) collected in midstream of the Tanshui River, northern Taiwan by laser-ablation inductively coupled plasma mass spectrometry.  The mullet averaged 300 33 mm in fork length and 410 141 g in body weight, and all were sexually immature at 1+ and 2+ yr old.  Strontium (Sr)/calcium (Ca) and barium (Ba)/Ca ratios in the otolith core indicated that the mullet in the river were from 2 different groups.  Group 1 (18%) fish had higher Sr/Ca ratios and lower Ba/Ca ratios in the otolith core region.  Group 2 fish (82%) were opposite to group 1, with higher Sr/Ca ratios and lower Ba/Ca ratios in the otolith core region, indicating that these mullet had resided in offshore waters in early life.  Beyond the core region, the Sr/Ca and Ba/Ca ratios alternately varied, indicating that the mullet migrated between brackish and freshwater habitats after the juvenile stage.  This study demonstrates that M. cephalus occupied diverse environments and migrated among marine, brackish, and freshwater habitats.  More study is needed to determine whether the mullet in the Tanshui River of Taiwan is a local population and its relationship to the well-known offshore migratory population that migrates to southwestern Taiwan to spawn in Dec.

Key words: Mullet, Freshwater fish, Otolith elemental composition, Migratory environmental history.

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