Post-Release Performance of Hatchery-Reared Tibetan Fish Schizopygopsis younghusbandi Juveniles in a Tributary of Lhasa River

Abstract

Stock enhancement is essential for China's fishery resource conservation. However, research evaluating the stocking effectiveness of plateau fish species is scare. Schizopygopsis younghusbandi, a Tibetan fish endemic to the middle Yarlung Zangbo River, is currently facing a decline in resource availability. In the present study, an 11-month mark–release–recapture experiment was conducted to evaluate the post-release performance of hatchery-reared juvenile S. younghusbandi released into a tributary of the Lhasa River from September 2023 to August 2024. The overall recapture rate of the released fish was 8.04%, with 92.0% of the individuals being recaptured within 10 days of their release. As the time since release increased, the occurrence rate of the released fish at various capture sites demonstrated a declining trend. The last recapture of a released fish occurred 248 days post-release, demonstrating that the experimental fish can successfully overwinter in the field environment. The average weight of the released fish increased by 66.4% over the 11 months following their initial release. The condition factors of the released fish exhibited notable variations, with a significant decline during the winter months. Changes in gut fullness indicate that the released fish resumed feeding as early as the second day post-release and maintained feeding activity throughout the subsequent experimental period. The movement patterns of the released fish reveal that they primarily dispersed upstream of the release site during the early stages; however, after 8 days of their release, they predominantly moved downstream. The population contribution rate of the released fish ranged from 0.36% to 1.09% over the 2–8 months following their release. The results of this study not only enhance our understanding of the adaptability of hatchery-reared plateau fish to wild environments but also provide a reference for the management and effectiveness evaluation of plateau fish stock enhancement programs.