Biochemical, histological, and gene expression analysis in brain and heart in Phoxinus lagowskii under sustained and diel-cycling hypoxia

Sustained and diel-cycling hypoxia frequently occurs in high-latitude environments; however, fish's biochemical, physiological, and histological responses to these two conditions remain unknown. Current hypotheses posit that the heart and the brain of fish from high latitudes are integral to their hypoxia tolerance and that fish exhibit different response mechanisms to cope with sustained and diel-cycling hypoxic conditions. To test this, we acclimated Phoxinus lagowskii, a high-latitude fish, to ecologically relevant sustained and diel-cycling hypoxia conditions over 28 days. Histological analysis revealed changes in the relative thickness of the layers in the midbrain. There was a prominent upsurge of oxidative stress biomarkers in diel-cycling hypoxia (DCH) treatments, with superoxide dismutase and catalase activity. Our data suggested that triglycerides in the heart were elevated in DCH groups but remained unchanged regardless of sustained hypoxia (SH) treatments. The majority of enzyme activities (LDH, PK, PFK, and HK) increased in DCH groups, especially at day 28. The gene expression results indicated that HIF mainly regulated long-term DCH in the heart and regulated SH in the brain. Collectively, these findings reveal that P. lagowskii exhibits varied adaptation strategies to the exposure of sustained and diel-cycling hypoxia.

Automated summary

This study investigated the biochemical, physiological, and histological responses of the high-latitude fish Phoxinus lagowskii to sustained and diel-cycling hypoxia. The results revealed that the fish exhibited different adaptation strategies to these two conditions.