engleski

Assessing the use of otolith morphometrics to predict the age of the black scorpionfish, Scorpaena porcus (Linnaeus, 1758)

The otoliths of the scorpaenids are relatively large and therefore easy to handle for the measurement of age, but numerous ramifications at the otolith edges can make the process of annual growth zones counting complex. One of the alternatives to this subjective, expensive and time consuming technique is the use of otolith morphometric parameters to derive the age of fish. To test the practicality and accuracy of the use of otolith morphometrics (length, width, thickness and mass) to estimate the scorpaenid age, we examined sagittal otoliths of 510 specimens of the black scorpionfish Scorpaena porcus, collected from the eastern Adriatic. The inner structure of the ground otoliths of S. porcus displayed an alternating pattern of translucent and opaque zones around an opaque nucleus. The annuli in the otoliths are laid down annually, the opaque zone being deposited in spring-summer and translucent zone in autumn-winter. Observed maximum ages for males and females were 10 and 12 years, respectively, although most of the sampled fish were 4 and 5 years old. The power model described the relationship between otolith morphometrics and age, explaining between 19.4% and 53.4% of the variation in age. The most precise age estimations were obtained from the otolith mass, followed by the otolith length, width and thickness. Relationship of the observed age and age estimated from all measured otolith morphometrics were described by a simple linear regression, accounting for 32.1% - 60.5% of the variation in estimated age. However, 95% confidence intervals did not include intercept =0 and slope =1 for all equations. Although the use of analysed otolith dimensions saved time and provided a similar population age structure to that of grounded otolith ages, this alternative method is not an accurate estimator of S. porcus age, primarily due to the length overlap between the different age classes.

age determination; otolith morphometrics; Scorpaena porcus

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