On the biology of the flat mouthed catfish Tachysurus platystomus (Day) from Mandapam

As determined from length-frequency studies, one-, two-, three- and fouryear- old fish respectively attain 178, 256, 310 and 366 mm size. As indicated by the opercular bone, the corresponding sizes were at 173, 256, 349 and 387 mm and as by vertebrae, they were 177, 272, 340 and 388 mm. Von Bertalanffy growth curve, fitted to the estimates of lengths at ages derived from opercular bone, is given as: Lj = 497.5 r , _ g - 0 35767 (1^(0.2305))' The length-weight relationship was significantly different for males and females. The low values of relative condition factor during December-February period was due to spawning. Yolked larvae were found to feed on planktonic organisms, even when they were in the mouth of the male parent. Even though the individuals of the species spawn only once and over a short period, the population as a whole may probably breed over November to February every year. Females and males first mature at 230 and 220 mm respectively. Fecundity varied from 32 to 40 ova in fish ranging from 230 to 390 mm in total length