UTTAR PRADESH JOURNAL OF ZOOLOGY

Sex-wise length–weight relationships and condition factors of Macrobrachium lamarrei were investigated in wild populations. The aim of the present study was to evaluate sex-wise length–weight relationships and condition factors of M. lamarrei from the Sone River, Bihar, across different length classes. The length–weight relationship showed negative allometric growth in males (b = 2.6154), females (b = 2.7443), and the pooled population (b = 2.6700), indicating that body weight increased at a slower rate than total length. The coefficient of correlation (r) was highest in males (0.9131), followed by the pooled population (0.9011) and females (0.8757), while the coefficient of determination (R^²) ranged from 0.7668 to 0.8338, demonstrating a strong relationship between length and body weight. Relative condition factor (Kn) values were generally greater than 1 across all length classes, indicating that individuals generally attained body weights comparable to or slightly higher than those predicted by the length–weight relationship. Variation in Fulton's condition factor (K) among different size classes indicated differences in somatic condition. Overall, the condition-factor indices indicated that the population of M. lamarrei in the Sone River maintained a favourable physiological status, while the negative allometric growth pattern provided useful information on size-dependent body development. Together, the length–weight relationship and condition factors of M. lamarrei provide basic information on the population structure and physiological condition of prawns and can serve as useful indicators for long-term ecological monitoring and assessment of habitat suitability for freshwater prawns.