Otolith microstructure and microchemistry were examined in the glass eels of 5 species of Anguilla to compare the early life histories among the New Zealand temperate eels A. dieffenbachii and A. australis, and 3 species of tropical eels (A. bicolor pacifica, A. marmorata and A. celebesensis) collected in Indonesia and the Philippines. The ontogenetic patterns of fluctuation in increment widths and changes in otolith Sr:Ca ratios were similar in all species examined. They all showed an abrupt increase in increment width and a sharp drop in Sr:Ca ratio, suggesting the onset of metamorphosis from leptocephalus to glass eel. However, age at metamorphosis was different among the 5 species, as was age at recruitment to estuary (average ± SD), which was 297 ± 25.3 d in A. dieffenbachii, 268 ± 31.3 d in A. australis, 195 ± 25.8 d in A. bicolor pacifica, 170 ± 15.9 d in A. marmorata and 116 ± 17.7 d in A. celebesensis. Ages at metamorphosis and recruitment showed a linear relationship in all 5 species, and both of these ages were greater for the New Zealand temperate species than for the tropical eels. A. dieffenbachii recruited to freshwater habitats at the largest size and after the longest larval duration of any species of Anguilla ever reported. This suggests that in New Zealand A. dieffenbachii spawns at a location where their leptocephali take longer to reach their freshwater habitat than A. australis. This is in contradiction to speculation that A. dieffenbachii spawns closer to New Zealand than A. australis, based on the more advanced stage of gonadal maturation that has been observed in the silver eels of the former species.KEY WORDS: Eel · Anguilla · Early life history · Otolith · Growth increments · Sr:Ca ratios · Metamorphosis · Inshore migration Resale or republication not permitted without written consent of the publisher

To determine the periodicity of the deposition of growth increments in the otolith of the glass eels of the tropical eel Anguilla marmorata, an otolith validation experiment was performed. Glass eels were captured at the mouth of the Poigar River, north Sulawesi Island, Indonesia, and then immersed in an alizarin complexone (ALC) solution to mark their otoliths. After being held under natural conditions in the river for 20 d, it was found that the number of rings outside the ALC mark was 20.1 ± 0.7 (mean ± SD), which coincided with the number of days after the ALC treatment. This validation experiment indicated that the growth increments in the otoliths of A. marmorata glass eels were deposited daily and can be used for daily age determination.

The otolith microstructure and microchemistry of a tropical eel, Anguilla marmorata, were examined in glass eels collected from Taiwanese and Japanese coasts. Ages at metamorphosis (onset of metamorphosis) and recruitment, respectively, were 114 ± 13.8 (mean ± SD) days and 144 ± 15.7 days in Taiwanese stock, and 123 ± 13.9 days and 154 ± 17.3 days in Japanese stock. No significant differences were found in ages between the two stocks. The duration of metamorphosis estimated from otolith microstructure was 10–24 days, which is the same in the different stocks. For both stocks examined, close linear relationships were found between ages at metamorphosis and recruitment, suggesting that individuals that metamorphosed earlier were recruited to the coasts at a younger age.

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