Effects of chronic cold stress and thermal stress on growth performance, hepatic apoptosis, oxidative stress, immune response and gut microbiota of juvenile hybrid sturgeon (Acipenser baerii ♀ × A. schrenkii ♂).

The current study was conducted to investigate the effects of chronic cold stress and thermal stress on the growth performance, hepatic oxidative status, immune response, apoptosis and gut microbiota in juvenile hybrid sturgeon. The fish (initial mean weight: 21.4 ± 0.3 g) was reared at three temperatures (14 °C, 22 °C, and 30 °C) for 16 d, which were termed as low temperature group (LT), moderate temperature group (MT), and high temperature group (HT), respectively, and the second group was regarded as control group in this study. Each group was assigned randomly to three tanks with 15 fish per replica. The results indicated that cold stress resulted in a significant reduction of growth metrics and a significant increase of feed conversion ratio in fish compared with MT group. Interestingly, cold stress increased hepatocyte apoptosis revealed by TUNEL staining, along with nuclear disappearance in H&E-stained sections and elevated serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels. Transcriptional levels of apoptosis-related genes and toll-like receptor signaling pathway components were significantly up-regulated in liver under cold stress. Compared with control group, in terms of thermal stress, the growth performance and feed utilization of fish were declined to some extent compared with MT group. Moreover, high temperature significantly elevated hepatic productions of malondialdehyde and hydrogen peroxide, as well as increased activities of some antioxidant enzymes in liver. In addition, low and high temperature induce changes in the composition of gut microbiota. Overall, the results suggested that cold stress decelerated growth performance, induced hepatocyte apoptosis, and enhanced innate immunity in hybrid sturgeon to cope with additional stressors. Whereas, thermal stress resulted in hepatic oxidative stress in liver and the protective responses in the antioxidant enzymes in fish were activated. These results provided insights into the different physiological adaptation strategies in responsive to cold stress and thermal stress in this cold-water fish.