Zoological Studies

Vol. 37 No. 3, 1998

Age of Pacific Tarpon, Megalops cyprinoides, at Estuarine Arrival and Growth during Metamorphosis

Wann-Nian Tzeng*, Chou-En Wu and Yu-Tzu Wang

Department of Zoology, College of Science, National Taiwan University, Taipei, Taiwan 106

Wann-Nian Tzeng, Chou-En Wu and Yu-Tzu Wang (1998) The age of Pacific tarpon, Megalops cyprinoides (Broussonet), at estuarine arrival was estimated by counting otolith growth increments from specimens collected in the Gongshytyan Brook estuary of northern Taiwan on 15 to 24 September 1995. The daily deposition of otolith growth increments provided a mean to estimate age of individuals. Tarpon at estuarine arrival were in the 1st metamorphic stage. Their body lengths ranged between 17.8 and 32.9 mm TL (mean = 25.6 mm TL) and ages between 20 and 39 d (mean = 28.5 d). A metamorphic mark within the otolith indicated that the fish had begun to metamorphose several days before arriving at the estuary. Negative correlations between age estimates, and both somatic and otolith growth rates indicate that faster-growing tarpon arrived at the estuary earlier than did slower-growing ones. Otolith growth continued while body length was reduced during metamorphosis. The duration of metamorphosis for Pacific tarpon was estimated to be approximately 14 d.

Key words: Megalops cyprinoides, Otolith, Age, Growth, Metamorphosis.

*Correspondence: Fax: 886-2-23636837. E-mail: wnt@ccms.ntu.edu.tw