The early life history of the tropical eel Anguilla marmorata (Quoy & Gaimard, 1824) from four Pacific estuaries, as revealed from otolith microstructural analysis

Anguilla marmorata glass eels or elvers were collected separately during anadromous migration from four Pacific estuaries: Hamuta, Poso, Shuang Hsi and Tanshui. The total length at arrival in these estuaries was (mean ± standard error) (51.50 ± 0.90) (51.80 ± 0.90) (46.95 ± 0.84) and (47.33 ± 0.80) mm, respectively. The sagittal otolith microstructure, increment patterns and daily age were examined by scanning electron microscope. Based on the number of increments of presumed daily deposition, the overall mean age at arrival in the estuaries was estimated to be about 3–4 months, with an estimated period of 73–86 days for the leptocephalus stage. Two zones, i.e. the leptocephalus growth zone (L) and the metamorphosis growth zone (M) were recognizable in the otolith cross section. The increment width of L and M varied from the otolith's centre to its margin, reflecting different growth rates. The spawning grounds of these eels are presumably not far from the estuary. Their locations are discussed.