Transcriptomic responses to heat stress in gill and liver of endangered Brachymystax lenok tsinlingensis

Global warming significantly affects fish, particularly cold-water fish, because increased temperature adversely impacts their abilities to grow or reproduce, and eventually influences their fitness or even causes death. To survive, fish may alter their distribution or behavior to avoid the stress, and perhaps acclimate or evolve resistance to the elevated temperature. Brachymystax lenok tsinlingensis is an endangered cold-water species in China, and it has been found to alter the altitudinal distribution, decrease swimming efficiency and develop resistance under heat exposure, which badly impact the continuing conservation work. To better protect them, it is essential to understand how they respond to thermal stress behaviorally and physiologically. Therefore, the fish were exposed to 24.5 degrees C and based on the time taken for them to lose equilibrium, they were separately sampled as sensitive and tolerant groups. Both gill and liver tissues were collected from both groups for transcriptome sequencing. Sequencing results demonstrated that control and tolerant groups were similar in transcriptomic patterns and sensitive groups differentially expressed more genes than tolerant ones, suggesting the gene expression of tolerant groups may return to base levels as exposure time increased. Tissue differences were the major factor affecting gene expression, and they also displayed different physiological responses to heat stress. Consistent with other studies, heat shock response, immune response, metabolic adjustment and ion transport were found to be triggered after exposed to elevated temperature. The findings would contribute to a better understanding of responding mechanisms of fish to thermal stress and provide guidance for future conservation programs.