The Relationship Between Sagitta Weight and Its Age in Japanese Grenadier Anchovy from the Yangtze River Estuary

Abstract: A total of 261 Coilia nasus were collected with stick net at the estuary of Yangtze River, Jingjiang, from January 2004 to April 2005. In each case sagittal otolith were removed, cleaned and dried 24h in an oven at 60°C and otolith weight were measured to the nearest 0.01mg. There were no significant differences in sagittal otolith weight between otolith in pairs(P>0.05), the left sagittal otolith was used in this research. According to linear, exponential and multinomial relationships among parameters, the highest correlations relationships were confirmedBThe relationship between sagittal otolith weight and the age of Coilia nasus and the use of otolith weight for validating annulus counts on otolith were being investigated. The results  indicated that sagittal otolith weight had little overlaps among age classes, and for individuals with similar body length, the older (slower-growing) was bigger in sagittal otolith weight than the younger (faster-growing). There were tremendous differences in sagittal otolith weight between different age classes and significant positive linear relationship with age (P>0.05). The age readings could be verified by plotting the sagittal otolith weight vs body length for age classes, and the individuals with similar body length but in different ages could be separated by sagittal otolith weight frequency analysis. It was demonstrated that the ‘estimated’ ages from regression between sagittal otolith weight and ages had no significant differences with the ‘counted’ ages from annulus counts on sagittal otolith. It was showed that the sagittal otolith weight analysis was a useful technique for validating the accuracy of age determination from annuli counting, especially for the individuals with similar size. Meanwhile, the potential of sagittal otolith weight analysis for direct estimation of ages of Coilia nasus was explored by the authors in this paper.