Integrated multi-tissue analysis reveals coordinated HPGL axis regulation of reproduction in Schizopygopsis younghusbandi under elevated temperature stress

Global warming-induced increases in water temperature in high-altitude aquatic ecosystems pose potential threats to the reproductive adaptation of cold-water fishes. However, the effects of thermal variation on hypothalamus–pituitary–gonadal–liver (HPGL) axis regulation and reproductive adaptation mechanisms remain unclear. In this study, the Tibetan endemic fish S. younghusbandi was exposed to four temperature conditions (12, 16, 20, and 22°C), and integrated histological analysis, hormone measurements, and multi-tissue transcriptomics were employed to investigate reproductive responses. The results showed that 16°C promoted HPGL axis activity, characterized by enhanced ovarian development, increased expression of GnRH, LHβ, FSHβ, steroidogenesis-related genes, and hepatic VTG, thereby facilitating reproductive development. In contrast, exposure to 20 and 22℃ induced oxidative stress, increased oocyte atresia, and reduced reproductive hormone levels, including E2, LH, and FSH. Transcriptomic analysis revealed that elevated temperatures disrupted hepatic PPAR signaling, suppressed lipid transport-related gene expression, and impaired lipid metabolic homeostasis, potentially affecting the nutrient supply required for ovarian development. Collectively, S. younghusbandi exhibits a narrow reproductive thermal window, with 16°C maintaining HPGL axis homeostasis, whereas temperatures above 20°C disrupt reproductive regulation through oxidative stress, lipid metabolic dysregulation, and impaired steroidogenesis. These findings provide new insights into the reproductive adaptation mechanisms of Tibetan cold-water fishes under climate warming scenarios.