Age and growth of filefish Thamnaconus modestus off Jeju Island

Abstract

The filefish (Thamnaconus modestus) has been commercially exploited in the southern waters of Korea. Samples were collected monthly by the commercial trawl catches landed during the period from May 2009 to December 2011 except January 2010 and December 2010 to March 2011. Of the 1698 specimens, the sex ratio was not significantly different from a 1:1 ratio (p>0.05). The total length was raged from 11.3 to 42.1 cm. The spawning occurred the period between May and June, and the Gonadosomatic Index (GSI) for both sexes was the highest in May to June, indicating May to June as the main spawning period. Length at sexual maturity of female was 25.92 cm. The length-weight relationship of filefish was W=0.0121 L 3.0536 (n=1692, r2=0.9034, p<0.001). The b-value of the length-weight relationship displays isometric growth with 95% confidence interval for b-value of 2.9950 – 3.0900. The age of the sampled individuals, which ranged from 0 to 9 years, was estimated using the count of growth ring recorded on the vertebrae. The filefish showed a high individual variation in total length at the same age. Length-at-age data were fitted using von Bertalanffy growth model. Estimation of the relationship between total length (TL, cm) and radius of vertebrae (VR, mm) was analyzed by the equation as following: TL=13.33+4.99VR for female and TL=15.41+4.13VR for male. The estimated von Bertalanffy growth parameters were L∞=42.04 cm, k=0.21 year-1, and t0=-1.56 for female; L∞=41.20 cm, k=0.18 year-1, and t0=-2.36 for male. These data can be used as biological information suitable for future fishery management of filefish resource in the Korean waters.