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.

The aim of this study was to investigate the circadian rhythm of muscle-related gene expression in mackerel tuna under different weather conditions. The experiment was carried out under two weather conditions at four sampling times (6:00, 12:00, 18:00, and 24:00) to determine the expression of growth, function, and rhythm genes: white muscle rhythm genes were rhythmic on sunny and cloudy days, except for PER3 and RORA; all functional genes had daily rhythmicity. Red muscle had daily rhythmicity on both sunny and cloudy days; functional genes had daily rhythmicity except for MBNL. The expression levels of the rhythm gene PER1 were determined to be significantly different by independent t-test samples in white muscle at 6:00, 12:00, 18:00, and 24:00 under different weather conditions; the expression levels of the functional genes MBNL and MSTN were both significantly different. In the red muscle, the expression of the rhythm genes PER3, REVERBA, and BMAL1 was determined by independent t-test samples at 6:00, 12:00, 18:00, and 24:00 on cloudy and sunny days; the functional gene MBNL was significantly different. The present study showed that mackerel tuna muscle rhythm genes and functional genes varied significantly in expression levels depending on weather, time of day, and light intensity and that the expression levels of myogenic genes were closely related to clock gene expression. The fish were also able to adapt to changes in light intensity in different weather conditions through positive physiological regulation.