Length-weight relationships and condition factors of three Mystus species (Teleostei: Bagridae) from upper Brahmaputra drainage, Northeast India

Length-weight relationships (LWRs) and condition factors for three bagrid catfishes of the genus Mystus (Siluriformes: Bagridae), viz., Mystus cavasius, Mystus vittatus and Mystus tengara were studied from the upper Brahmaputra drainage, Northeast India. LWRs and condition factors for each species (separately for male, female and combined sex) were evaluated based on the log-transformed length-weight data derived from a total of 885 individuals sampled between June 2024 and July 2025. LWRs are important as they provide essential information on fish growth patterns and population dynamics are widely applied in fisheries management and stock assessment. Species-wise, the parabolic equation for the combined sex was established as W = 0.0228 L2.454 for M. cavasius (n = 342), W = 0.0331 L2.410 for M. vittatus (n = 335) and W = 0.0440 L2.277 for M. tengara (n = 208). All LWRs were significant (p < 0.05) and highly correlated, as estimated R2 values were found to be 0.768, 0.842 and 0.834 for M. cavasius, M. vittatus and M. tengara respectively. All three species studied show negative allometric growth with ‘b’ values ranging from 2.277 to 2.454. The mean Fulton’s condition factor (K) ranged from 0.65 (M. cavasius) to 1.07 (M. vittatus), whereas the relative condition factor (Kn) found to be 1.04 for M. vittatus and 1.01 for both M. cavasius and M. tengara, indicating a state of well-being and good growth conditions for all three Mystus species. The present study contributes valuable baseline data on the growth and health status of three commercially important Mystus species from the upper Brahmaputra drainage, which can support sustainable management and conservation strategies.