One of the important aspects of fish biology is the length weight relationship and relative condition factor. In the hillstream fish Mastacembelus armatus, a relationship between total length and body weight was studied sex wise and season wise. The length and body weight ranged from 10 to 59.2cm. and 7.0 to 250 gm. in males and 21.2 to 56.3 cm. and 37 to 229 gm. in females respectively. The regression coefficient for sex wise and pooled data varied from a maximum of 3.997 for male (r = 0.794) and minimum of 3.977 for female (r = 0.414) fishes. Sex wise seasonal data ranged from 1.811 (r = 0.207) during the autumn months to 5.658 (r = 0.820) during summer for the males. However, in female it ranged from 4.043 (r = 0.339) during autumn to 6.682 (r = 0.245) during summer seasons. The relative condition factor was maximum for males as 1.265 ± 0.199 and for females 1.339 ± 0.074 in the month of February. The lowest value was observed 0.779 ± 0.167 for males and 0.888 ± 0.058 for females in the month of July. Season wise the Kn values were observed high 1.016 ± 0.181 for males and 1.009 ± 0.229 for female fishes in spring. It is also observed that the second next peak values were found during winter for both sexes (For male: 1.003 ± 0.391 and female: 1.002 ± 0.411) which represent good condition of fish on the basis of active feeding and suitability of the environment.
