Length-weight and length-length relationships of 20 fish species from the Kezilesu River, China

Introduction The Kezilesu River, a tributary of the Tarim River in Xinjiang, China, supports a unique but poorly studied fish fauna. This study provides the first comprehensive analysis of length-weight relationships (LWRs) and length-length relationships (LLRs) for fish species in this data-poor but ecologically significant ecosystem of Northwest China. Methods A total of 2,184 specimens belonging to 20 fish species were collected from the Kezilesu River between January 2020 and December 2024 using multi-mesh nylon gillnets and cage nets. For each specimen, total length (TL), standard length (SL), and body weight (W) were measured. The LWR parameters were estimated using the linear regression model log(W) = log(a) + b·log(TL), and LLRs were established using linear regression (TL = a + b·SL). Results The LWR parameter b varied from 2.844 (for Schizothorax biddulphi) to 3.250 (for Esox lucius), with all regressions being highly significant (P < 0.001) and coefficient of determination (r²) values exceeding 0.91. The LLR parameter b ranged from 1.095 (for Triplophysa tenuis) to 1.168 (for Schizothorax irregularis). This study presents the first LWR and LLR records, as well as new maximum lengths, for five endemic species: Schizothorax irregularis, Schizothorax eurystomus, Schizothorax biddulphi, Triplophysa tenuis, and Triplophysa yarkandensis. Discussion These findings provide fundamental biological data crucial for the sustainable management and conservation of fishery resources in the Kezilesu River, contributing to the understanding of fish biology in arid-land river ecosystems of Northwest China.