Ageing of shortspine spurdog in the Andaman Sea of ThailandPublished on 04. April 2013
Ageing of shortspine spurdog in the Andaman Sea of Thailand
Kanokwan Paiboonleeskul, Suppaluk Romratanapun and Thanitha Thapanand-Chaidee
Shortspine spurdogs( Squalus mitsukurii ) were sampled from the Andaman Sea of Thai waters with bottom vertical longline and deep sea traps. The total length (TL) of the individual sample was measured and the second dorsal spine was removed. The number of growth bands on the external surface of the spine were counted using a dissecting microscope. Sixty-five S. mitsukurii (20 males and 45 females) were used in this study. TL of the fish ranged from 43.4 – 72.1 cm for females and 44.9 – 50.5 cm for males. The estimated ages were 4 – 12 years old. The relatively low coefficient of variation (CV) values at 22.90% implies the consistency of age – reading between the two readers and make merit to the estimated ages. The relationship between the enamel base diameter (EBD) and TL is positively linear as EBD = 10.66 + 7.58TL (R² = 0.751, Sy.x = 0.07). The result from ANCOVA indicates that there is no significant difference in the lengths at any given age between males and females ( F = 0.9966, p =0.3221). The EBD from the second dorsal spine of S.mitsukurii can be used to determine its age. The ageing method by sectioning the spine can also be employed to verify the estimated age from the external surface of the spine. The age reading taken from the external surface compared to the cross – sectioned spine shows no significant difference (X2= 0.848, p = 1.000). The age reading for S. mitsukurii is therefore easily determined from the external band of the second dorsal spine.
Maejo Int. J. Sci. Technol. 2013 , 7 (Special Issue), S. 14-21