# Effects of High-Flow-Velocity Stress on Energy Metabolism and Transcription Level of Triplophysa orientalis

## TL;DR

This study shows how a type of fish adapts to fast water currents by changing its energy metabolism and gene activity.

## Contribution

The study identifies specific gene expression changes in Triplophysa orientalis under high-flow conditions, revealing metabolic reprogramming for survival.

## Key findings

- High-flow velocity down-regulates genes involved in mitochondrial energy production and oxidative phosphorylation.
- Stress response and oxygen-handling genes like UCP3 and cygb1 are up-regulated under high-flow conditions.
- Transcriptional changes suggest metabolic reprogramming to cope with hydrodynamic stress in T. orientalis.

## Abstract

River channel modification and hydropower development can create unusually fast currents that force stream-dwelling fishes to swim harder, spend more energy, and experience greater physiological stress. We examined how a plateau loach (Triplophysa orientalis) responds to strong water flow at the gene-expression level. Fish were exposed for 3 days to a normal current (3 body lengths per second) or a high current (33 body lengths per second) in a controlled circular swimming system. By sequencing muscle RNA and validating key targets with qPCR, we found that high flow changed the expression of a small set of genes (78 in total). High flow altered 78 genes (55 up-regulated and 23 down-regulated). Specifically, multiple genes involved in mitochondrial energy production (oxidative phosphorylation) were strongly down-regulated, whereas genes linked to oxygen handling and limiting reactive oxygen species increased; for example, UCP3 and cygb1 were up-regulated with log2 fold changes of 3.19 and 3.93. At the same time, several genes associated with antioxidant transport and cellular stress protection showed a decreasing trend. Together, these patterns suggest that T. orientalis undergoes metabolic reprogramming under sustained high flow—shifting how energy is produced and allocated to cope with hydrodynamic stress—which could help survival but could constrain energy available for growth.

River channel development and hydraulic engineering alter natural flow-velocity patterns, subjecting Triplophysa orientalis to heightened hydrodynamic stress and energy expenditure in high-flow-velocity habitats. Regulating the molecular regulatory mechanisms underlying their adaptation to high-flow velocities provides a basis for species conservation and habitat optimization. Fish were exposed for 3 days to a normal flow velocity (3 BL/s) or a high flow velocity (33 BL/s) in a controlled circular swimming system that maintained a stable current without a deliberate low-flow velocity refuge; fish at 33 BL/s sustained upstream swimming throughout the exposure. RNA-seq differential expression analysis and GO/KEGG enrichment were performed on harvested skeletal muscle, with key genes validated via qPCR. A total of 78 differentially expressed genes (DEGs) were identified between the high-flow-velocity group and the normal-flow-velocity group, including 55 up-regulated genes and 23 down-regulated genes. GO and KEGG analyses revealed that the DEGs were predominantly enriched in mitochondrial energy metabolism and neural regulation, notably oxidative phosphorylation, and were further linked to FoxO and IL-17 signaling. Compared to the normal-flow-velocity group, the high-flow-velocity group exhibited significant down-regulation of multiple oxidative phosphorylation-related subunits, including Mt-co1, Mt-co2, Mt-co3, Mt-nd1, Mt-nd2, Mt-nd4, Mt-nd5, and Mt-atp6. Concurrently, stress response-related genes, such as Selenop, GADD45B, and SIK2, showed a down-regulation trend. These transcriptional changes are consistent with reduced expression of genes involved in antioxidant defense and cellular protection under high-flow conditions, integrating differential-expression and pathway-enrichment results. This decline correlates with the down-regulation of genes associated with antioxidant and stress regulation. Pathways related to energy metabolism show significant enrichment, suggesting enhanced regulation of energy supply and allocation. This pattern indicates metabolic reprogramming characteristics adapted to high-flow-velocity stress.