Age and growth of the marine catfish Tachysurus thalassinus (Ruppell) from Mandapam waters

Employing six different methods, the age and growth of Tachysurus thalassinus at Mandapam are determined. By length-frequency, it is found to attain 250 mm at the end of first year, 370 mm the end of second year and 450 mm the end of third year. By the probability plot, four year-classes are recognized: I to IV, respectively at 256 mm, 360 mm, 454 mm and 522 mm. Transparent rings in the pectoral-spine sections showed that the species attains 258.3 mm at the end of one year, 347.4 mm at the end of two years and 441.6 mm at the end of three years. The lengths at age as derived from vertebral studies are 260.9 mm in one year, 355.9 mm in two years and 436.5 mm in three years. Based on alternating opaque and transparent zones in the opercular bone, the mean back-calculated lengths at the ages one to three are 251.3 nmi, 345.5 mm and 445.1 mm, respectively. The embryos of T. thalassinus reared in the aquarium, under controlled conditions, showed, however, the rate of growth to be slightly higher. The von Bertalanffy growth equation for this species can be expressed as: Lt = 848.5 (l-e-0.t»885 (t0.8li3