Oxygen level is an important environmental factor affecting the circadian rhythm. However, little is known about the molecular mechanism by which clock genes regulate the circadian rhythm in fish under hypoxia. To explore changes in the transcription and expression of clock genes and related molecular regulatory mechanisms in pearl gentian grouper under hypoxia, liver transcriptome data were analyzed after exposure to acute hypoxic stress (dissolved oxygen 0.5 mg/L) for 1, 3, 6, and 9 h. miR-210 and m0044-5p inhibited the expression of period3 (per3) and casein kinase 1 delta b (csnk1db) in the core loop of the circadian clock, respectively. The nuclear receptor subfamily 1 group d member 1 (nr1d1) and RAR-related orphan receptor b (rorb) genes in the auxiliary loop were jointly up-regulated by three miRNAs (miR-144-3p/5p, miR-361-5p, and miR-133) and the transcription factor nuclear receptor subfamily 1 group d member 2 (Nr1d2). The pearl gentian grouper maintains the stability of circadian clock systems and normal physiological metabolism under hypoxic stress by regulating the transcriptional expression of these genes via miRNAs and transcription factors to improve hypoxic tolerance. These findings provide important basic data for future research on hypoxic tolerance in pearl gentian grouper and provide new insights into the interaction between hypoxia and the circadian rhythm in fish.
