Age and growth of filefish, Thamnaconus modestus (Gunther, 1877) off the Jeju Island of Korea

The age and growth of filefish, Thamnaconus modestus (Gunther 1877) in the southern waters of Korea were investigated. Samples were collected with commercial trawl catches during the period from May 2009 to December 2011. Of the 2,626 specimens collected, the sex ratio was not significantly different from 1:1 (P > 0.05). The total length ranged from 11.3 to 42.1 cm. The gonadosomatic index for both sexes was the highest in May to June, indicating that May to June is the main spawning period. The length of females at sexual maturity was 25.92 cm. The length-weight relationship of the filefish was TW = 0.0121TL(3.0536) (n = 1,692, r (2) = 0.9034, P < 0.001). The age of the sampled individuals was estimated by counting growth rings recorded on the 5(th) vertebrae; ages ranged from 0 to 9 years. The filefish of the same age displayed a high individual variation in total length. Length-at-age data were fitted by using the Von Bertalanffy growth model. The estimated Von Bertalanffy growth parameters were L (a) = 42.04 cm, k = 0.21 year(-1) and t(0) = -1.56 for females, L (a) = 41.20 cm, k = 0.18 year(-1) and t(0) = -2.36 for males, and L (a) = 43.16 cm, k = 0.17 year(-1) and t(0) = -2.18 for the combination of both male and female. These data can be used as useful biological information for the future fishery management of filefish resources in Korean waters.