| AN EVALUATION OF THE OTOLITH CHARACTERISTICS OF CONGER CONGER DURING METAMORPHOSIS |
| CORREIA, A.T., Antunes, C., Wilson, J.M. and Coimbra, J., Centro Interdisciplinar de Investigação Marinha e Ambiental, Rua dos Bragas 289, 4050-123 Porto, Portugal, atcorreia@cimar |
| A sample of twenty metamorphosing conger eel leptocephali were collected from the Minho River in February 1999. Sagittal otoliths were analysed by scanning electron microscopy. Four different etching agents were applied along both sagittal and frontal sections during otolith preparation. Otolith growth increments were visible along the increment countable zone. However, a permanent peripheral diffuse zone, where the daily increments are unclear, appeared on all otoliths, preventing the accurate age estimation. In an attempt to solve this problem, otoliths of ten other metamorphosing leptocephali reared in aquaria were marked by immersion in tetracycline hydrochloride for one day. The distance between the fluorescent marks and otolith edge, measured over a fixed period of time, was used to estimate the otolith growth rate. The application of this technique led to an anomalously high estimated otolith growth rate, probably as a result of the capture, marking and handling stress. |
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