The Comparison of Different Pre-treatment Methods for Acquiring Otolith Annuli of Coilia nasus

Abstract:

Estuarine tapertail anchovy Coilia nasus has been a highly popular and commercially valuable anadromous species in China the texture of which is delicate. Recently age estimation by otolith of this fish has become a hotspot in ecological research, which largely depends on efficient pre-treatment methods that generate clearer annual rings in the otolith of C. nasus. In this study we compared the effectiveness of several pre-treatment methods. The results showed that the transverse plane was clearer than the sagittal plane through the core; however, the latter was more suitable in some special analysis (especially microchemistry). Etching with 5% EDTA produced a clearer surface than 1% HCl. Analysis on the rings in the sagittal planes after etching suggested that the morphological change in the otoliths was correlated with transition in the habitat during the lifetime. In conclusion, the transverse plane is suitable for determining the age, and the sagittal plane is optimal in microchemical analysis.