A Comprehensive Study on the Growth and Population Dynamics of Endemic Fish Ptychobarbusleptosomus in the Yalong River

Ptychobarbus leptosomus is a newly identified endemic fish species distributed in the mid-upper Yalong River drainage on the Qinghai-Xizang Plateau, yet its basic biology and population status remain scarcely documented. This study combined growth characteristics and population dynamic analyses to elucidate its adaption to the plateau environment and assess current resource status, thereby providing a scientific basis for effective conservation measures. A total of 111 specimens were collected from the mid-upper Yalong River during 2022 to 2024. Based on biometric data including body length, body weight, age, and gonadal developmental stage, key growth parameters were derived. Population dynamics and resource status were assessed through biological reference points, a yield-per-recruit (YPR) model, and spawning potential ratio (SPR) model. The length-weight relationship showed isometric growth in both females (b=3.0218) and males (b=3.0491), with no significant deviation from 3. Growth coefficients (k) were low (0.0574 for females, 0.0687 for males), reflecting slow growth typical of plateau-adapted fishes. The estimated length and age at first sexual maturity were 33.79 cm and 8.518 years for females, and 32.14 cm and 7.451 years for males. Age at first capture peaked at 7.09 years for females and 5.83 years for males. Total mortality (Z) was estimated at 0.482/a for females and 0.460/a for males. Critically, SPR values ranged between 0.35—0.43 for females and 0.30—0.39 for males, both well below the F25% reference point, indicating severe overexploitation. The above results showed that P. leptosomus exhibits a long life span, slow growth, and late sexual maturity, and that its population is under heavy fishing pressure. Urgent targeted protection measures are needed to promote resource recovery and ensure population persistence.