Validation of otolith daily increments in the tropical eel Anguilla celebesensis

Abstract

To validate daily increments in otoliths of the tropical freshwater eel Anguilla celebesensis, a time-reference mark was incorporated in the otoliths of glass eels by immersing the eels in alizarin complexone (ALC) solution. They were subsequently reared in aquaria for 10 or 20 days, and the increments outside a fluorescent red ALC mark were counted. The numbers from the 10- and 20-d experiments were 9.4 ± 0.9 (mean ± SD) and 19.4 ± 1.4, respectively, suggesting daily deposition of otolith increments. Precise examination of otolith microstructure from the core to the edge showed gradual changes in increment width with no discontinuous structural features, suggesting that increments were deposited continuously from hatching to time of sacrifice. It was thus concluded that otolith increments in this species can be used for daily age determination.