*Article* **Daily Rhythmicity of Hepatic Rhythm, Lipid Metabolism and Immune Gene Expression of Mackerel Tuna (***Euthynnus affinis***) under Different Weather**

**Wenwen Wang 1,2,†, Jing Hu 1,2,†, Zhengyi Fu 1,2,3, Gang Yu 1,2 and Zhenhua Ma 1,2,3,\***


**Abstract:** In order to investigate the rhythmic changes in gene expression in the liver of mackerel tuna (*Euthynnus affinis*) under sunny and cloudy conditions, this experiment had four sampling times (6:00, 12:00, 18:00 and 24:00) set on sunny and cloudy days to determine the expression of their immune, metabolic and rhythmic genes. The results showed that daily rhythmicity was present within most of the rhythm genes (*CREB1*, *CLOCK*, *PER1*, *PER2*, *PER3*, *REVERBA*, *CRY2* and *BMAL1*), metabolic genes (*SIRT1* and *SREBP1*) and immune genes (*NF-kB1*, *MHC-I*, *ALT*, *IFNA3*, *ISY1*, *ARHGEF13*, *GCLM* and *GCLC*) in this study under the sunny and cloudy condition (*p* < 0.05). The expression levels of *CREB1*, *PER1*, *PER3*, *RORA*, *REVERBA*, *CRY1* and *BMAL1* within rhythm genes were significantly different (*p* < 0.05) in the same time point comparison between sunny and cloudy conditions at 6:00, 12:00, 18:00 and 24:00; metabolic genes had the expression levels of *LPL* at 6:00, 12:00, 18:00 and 24:00 in the same time point comparison (*p* < 0.05); immune genes only had significant differences in the expression levels of *IFNA3* at 6:00, 12:00, 18:00 and 24:00 (*p* < 0.05). This study has shown that rhythm, lipid metabolism and immune genes in the livers of mackerel tuna are affected by time and weather and show significant changes in expression.

**Keywords:** cosinor analysis; biological clock; circadian rhythm; gene expression
