To understand the physiological reactions of juvenile yellowfin tuna (Thunnus albacares) under acute high-temperature stress, this study measured the changes in biochemical indexes of serum, liver, gill, and muscle of yellowfin tuna under acute high-temperature stress (HT, 34 °C) and a control group (28 °C) for 0 h and 6 h, 24 h and 48 h. The rising speed of water temperature in the HT group was 2 °C/h and the timing started when the temperature reached 34 °C. In the HT group, there was no significant difference between the four adjacent times in cortisol and lactic acid concentration. Serum triglyceride, cholesterol, and alkaline phosphatase concentration were significantly different from the four adjacent times. The superoxide dismutase (SOD) activity in the liver and gills increased at 6 h and 24 h, and the gills and liver had antioxidant reactions in a short time. The malondialdehyde (MDA) concentration in the gills changed significantly at 6 h, while that in the liver did not change significantly. The gills were more sensitive to temperature stress than the liver and muscle. Acute high-temperature stress affected yellowfin tuna’s antioxidant enzymes and metabolic indexes, resulting negative trend in physiological indexes, indicating that yellowfin tuna juveniles are susceptible to elevated temperature.

The uplift of the Qinghai–Tibet Plateau has shaped a unique extreme environment, fostering distinct endemic aquatic organisms. Schizopygopsis pylzovi, a vulnerable endemic fish in the upper Yellow River, is a key model for studying the biogeographic patterns of plateau fish. To assess its genetic characteristics and evolutionary dynamics, we comprehensively evaluated 11 geographic populations of S. pylzovi using two complementary mitochondrial markers, the conserved COI gene and the fast-evolving D-loop region. A total of 142 COI and 143 D-loop sequences were analyzed, and sequences alignment, haplotype network construction, AMOVA, and neutrality tests were performed. AMOVA revealed that genetic variation was mainly distributed within populations, indicating weak population differentiation. Neutrality tests and mismatch distribution analysis suggested historical and recent population expansion events. Our findings highlight the value of joint analysis using COI and D-loop markers in revealing the genetic structure of S. pylzovi, provide new insights into the impact of plateau uplift on fish evolution, and establish a scientific basis for the conservation of this vulnerable species.