Chronic heat stress caused by global warming can have serious implications for fish survival. The kidney plays a central role in many homeostatic functions, including water and electrolyte regulation. However, there is limited knowledge about the effect of heat stress on fish kidneys. In this study, water temperatures were increased from 20 °C to 24 °C and 28 °C in 8 days at a warming rate of 1 °C/d, and then maintained for 12 days. We investigated the effects of mild heat stress (24 °C) and high heat stress (28 °C) on Siberian Sturgeon (Acipenser baerii) kidneys using histological observation, flow cytometry detection, and RT-qPCR. Our histological observations revealed that heat stress caused significant infiltration of inflammatory cells in the kidney, especially at 28 °C. The flow cytometry assay demonstrated a significant increase in the number of apoptotic cells after heat stress at 28 °C compared to a control group at 20 °C (p = 0.033). The level of plasma creatinine was significantly increased in the 28 °C group compared to the control group (p = 0.001). In addition, the mRNA expression levels of heat shock protein GRP75 increased (p = 0.009). The results indicate that heat stress at 28 °C caused damage to the kidneys of A. baerii and triggered the protective response of heat shock proteins. In conclusion, this study contributes to the understanding of the coping strategies of the kidney of A. baerii for chronic heat stress.

The hybrid sturgeon Acipenser baerii × A. schrenckii is the most widely cultured commercial sturgeon in China. However, its morphological similarity to the parental species frequently leads to misuse of germplasm in the breeding process, resulting in a decline in the quality of the sturgeon production. In this study, we have developed a protocol by using mitochondrial DNA barcoding and microsatellite locus analysis for the accurate identification of sturgeon species. Genetic distance and phylogenetic analysis based on the mitochondrial COI segment showed that A. baerii exhibited the closest genetic relationship with orthogonal individuals A. baerii (♀) × A. schrenckii (♂). Conversely, A. schrenckii displayed the highest genetic similarity with reciprocal individuals A. schrenckii (♀) × A. baerii (♂). Additionally, genetic structure analysis and factor correlation analysis (FCA) were conducted using six microsatellite loci among 100 samples, including eight species and two hybrid sturgeon. The results showed that all samples, encompassing both hybrid sturgeon (A. baerii × A. schrenckii) and their parental species, were accurately grouped into ten clusters, thereby validating the precision of this species assignment method.