Biological characterization of wild cobia, Rachycentron canadum (linnaeus, 1766) off Dungun coast, Terengganu, Malaysia for stock management and aquaculture

Investigation of some aspects of biology of a recreationally and commercially important fish, cobia, Rachycentron canadum in Dungun coast, Malaysia was conducted between April 2014 and May 2015. A total of 249 specimens were opportunistically collected from the catches of trawl net, gill net and by hooks and line. The total length ranged from 39.20 to 143.00 cm (88.29 ± 1.28 cm), fork length ranged from 37.50 to 124.00 cm (78.69 ± 1.09 cm) while the wet weight ranged from 0.50 to 20.40 kg (5.51 ± 0.26 kg). There was no significant difference in all the morphometric characters between sexes except for head width (HW) (p < 0.05). Ten (10) out of the seventeen (17) truss distances in the body landmarks of cobia showed significant differences between males and females. The equation of length-weight (LW) relationship for combined sex was W = 0.000002FL3.3204 (R² = 0.92). The growth of cobia in Dungun water followed positive allometric as the growth coefficient (b) was higher than 3. Observed length frequency of both sex followed a normal distribution pattern and there was a predominance of cobia in the medium size range from 65 - 85 cm fork length for the females and 55 - 90 cm for the males. The sex ratio of females to males was 1:1.18 and it was not significantly different from the expected 1:1 (X2 = 2.12 df = 1; p < 0.05). Growth parameters of von Bertalanffy growth formula for cobia estimated were L = 142.00 cm, K = 1.20 yr-1, while natural mortality rates (M), fishing mortality rate (F), total mortality (Z) and Exploitation rate (E) estimated were 1.34, 0.95, 2.29 and 0.41 respectively. The maximum allowable limit of exploitation (Emax) was estimated to be 0.56. The sizes attained by cobia at the end of age 1 (year) was 99.28 cm. The estimation of fork length at first maturity (Lmat) from the plot of gonadosomatic index (GSI) against fork length (FL) indicated early maturation of males compared to females with respective value of 70 cm and 72 cm. Males with mature g