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要旨

Juvenile Triportheus albus (Characidae) were sampled with a ringnet in the Central Amazon floodplain between March and April 1993. The microstructure of the otoliths of T. albus was analyzed under the scanning electron microscope. The lapillus shows regular increments when ground in the sagittal plane and can be utilized for age determination. There are marks or checks formed at intervals of 14 rings, sometimes of 7 rings. Broad increments (>4.5 mum) rarely show subrings. The first 160 increments can be counted easily. In individuals which are bigger than 100 mm the microstructures at the edge are often undistinguishable. The calculation by counting of the increments yields an estimated daily growth of 0.426 mm (p <0.01) for juveniles of T albus