Population Structure and Resource Dynamics of Three Schizothoracinae Species in the Duoxiong Zangbo River Tributary of the Yarlung Zangbo River, Tibet: Threat Assessment and Conservation Insights

The Yarlung Zangbo River (With a total length of 2057 km, the river forms part of the Ganges-Brahmaputra River system), located in the core region of the Tibetan Plateau, hosts a unique yet fragile aquatic ecosystem. Fish populations inhabiting this ecosystem have been significantly impacted by external factors, leading to declining resources. This decline is particularly evident in local tributaries, including the DuoXiong Zangbo River-a main tributary where scientific research remains scarce due to its geographic remoteness. Consequently, the status of schizothoracinae in this river remains poorly understood, necessitating research on their population structure, growth characteristics, and resource dynamics, as well as the extent of external disturbances. During the 2023-2024 season, fishery surveys were conducted during two sampling periods: summer (June-July) and autumn (September-October). This study focuses on the Duoxiong Zangbo River, a tributary of the Yarlung Zangbo River, targeting three schizothoracinae fish species: <i>Schizothorax o'connori</i>, <i>Oxygymnocypris stewartii</i>, and <i>Ptychobarbus dipogon</i>. The results show that their body lengths ranged from 23.02 to 440.00 mm, 23.02 to 460.00 mm, and 45.18 to 418.00 mm, with body weights ranging from 0.30 to 1394.30 g, 0.20 to 1013.00 g, and 1.20 to 814.30 g. Age distributions spanned 0-14, 0-16, and 0-13 years, respectively, indicating a trend toward younger and smaller individuals. Von Bertalanffy growth modeling revealed asymptotic body lengths (<i>L</i>_∞) of 591.233 mm, 507.557 mm, and 515.292 mm, with growth coefficients (<i>k</i>) of 0.098, 0.122, and 0.118, respectively. These parameters suggest that the populations are exhibiting accelerated growth strategies in response to fishing pressure. Using FiSAT II, exploitation rates (<i>E</i>) were calculated as 0.547, 0.758, and 0.711 for the three species, with predicted maximum sustainable exploitation rates of 0.579, 0.882, and 0.884, respectively. These findings indicate that the three schizothoracinae species have approached the threshold of overexploitation and are facing threats of overexploitation. In summary, this study demonstrates that schizothoracinae in the DuoXiong Zangbo River are experiencing adverse effects from external pressures, with populations at risk of decline. These results underscore the urgent need for targeted conservation and management strategies.