To explore the differences in circadian behavioral rhythms and the changing regularity of different fish species, and improve artificial culture technology, we analyzed and compared the circadian behavioral rhythms of Hippocampus kuda and Oryzias melastigma under the artificial culture conditions detailed in this paper. The results showed that under the conditions of light intensity of 2000 lx, temperature of 25±1 ℃, salinity of 25±0.5, and photoperiod of 14L : 10D, the behavioral rhythms of H. kuda and O. melastigma during the daytime are stronger than in the nighttime. H. kuda showed the strongest rhythm and the most abundant behavioral component between 08:00 and 10:00. The macroscopic behavior components included active behaviors (swimming 47.40±1.1%, crawling 3.0±0.6%, moving 4.80±0.7%), and inactive behaviors (swing 32.50±2.1%, resting 12.30±0.8%). The microcosmic behavior components included gill operculum movement 38.77±1.14 times/min, jaws movement 38.77±1.14 times/min, and eyeball rotation 108.50±5.52 r/min, dorsal fin movement 116.87±0.64 times/min and pectoral fin movement 67.81±2.27 times/min. The sub-strongest rhythmic period was 12:00–14:00, and the rhythmic behaviors were dominated by swinging with a percentage of 59.20±5.1%. O. melastigma also had the strongest activity between 08:00 and 10:00, in which the percentage of swimming amounted to 88.0±1.1%; the frequency of gill operculum movement was 407.88±3.8 times/min, jaw movement 407.88±3.8 times/min, eyeball rotation 7.38±0.9 r/min, dorsal fin movement 373.17±2.5 times/min, pectoral fin movement 400.83±6.8 times/min, and tail movement 416.58±7.7 times/min. Therefore, both H. kuda and O. melastigma have strong circadian behavioral rhythms, and the period of 8:00–10:00 is their peak period of behavioral activity, which is the strongest rhythm and the most abundant behavioral components. Therefore, the period of 08:00–10:00 can be selected as a suitable observation time for related behavioral studies.