Behavioral responses and transcriptional dynamics of the stream fish (Acrossocheilus fasciatus) under temperature change

Global warming and extreme weather events are exerting significant thermal stress on aquatic species, particularly fish, affecting their metabolism, behavior, immunity, and reproductive strategies. Despite extensive research on the effects of thermal stress on aquatic organisms, there is a gap in understanding how short-term temperature fluctuations influence both behavior and transcriptional dynamics in high-elevation stream fish. We addressed this gap by investigating the effects of temperature variability on the behavior and transcriptomic profiles of Acrossocheilus fasciatus , a commercially valuable, widely distributed, eastern Asian stream fish. We applied two temperature treatments (32 ​°C and 16 ​°C) and two conditions (continuous exposure and temperature recovery) to assess behavioral responses and changes in cortisol and 5-hydroxytryptamine(5-HT) levels. High temperatures increased movement speed and turning angles, whereas low temperatures decreased movement frequency and speed. Low temperatures led to a significant rise in 5-HT, whereas high temperatures caused a decrease. Concurrently, brain transcriptomic analysis identified substantial differential gene expression related to behavioral plasticity and cellular stress responses. Key enriched pathways included circadian rhythm, oxidative phosphorylation, and prolactin signaling, indicating the fish's physiological adaptation to temperature changes. We conclude that high temperatures have a substantial affect on the behavior and transcriptional dynamics of A. fasciatus , including increased aggression and cellular damage, whereas cold temperatures have minimal effects. Fish exposed to temperature recovery conditions demonstrated effective behavioral adaptation. These findings highlight the heightened sensitivity of stream-dwelling fish to thermal extremes and underscore the need for further research on their adaptive mechanisms and long-term effects. • Prolonged heat stress disrupts fish circadian rhythms, altering behavior and schooling character. • Transcriptome analysis shows short-term heat damages. • Timely recovery reduces heat-stress induced harm.