Oxygen consumption (OC) of male black porgy Acanthopagrus schlegelii reared in freshwater (BFW) and seawater (BSW) during the reproductive period was $165.4{pm}11.0$, $77.6{pm}8.0$ mg $O_2/kg/h$ at $15^{circ}C$, $186.2{pm}13.1$, $133.4{pm}6.7$ mg $O_2/kg/h$ at $20^{circ}C$ and $267.9{pm}19.1$, $198.6{pm}8.3$ mg $O_2/kg/h$ at $25^{circ}C$, respectively. During the non-reproductive period, it was shown as $174.0{pm}7.0$, $85.6{pm}5.5$ mg $O_2/kg/h$ at $15^{circ}C$, $200.6{pm}11.1$, $119.2{pm}8.7$ mg $O_2/kg/h$ at $20^{circ}C$ and $271.1{pm}7.5$, $194.7{pm}16.7$ mg $O_2/kg/h$ at $25^{circ}C$, respectively. Thus, OC of BFW was higher than BSW both for non-reproductive and reproductive period. Also, OC increased in proportion to the rise in water temperature, and there was no difference of OC between BFW and BSW at each water temperature during the reproductive or non-reproductive period. OC of BFW and BSW showed clear circadian rhythms on photic conditions of reproductive and non-reproductive period, and the fish consumed more oxygen during the dark phase than for the light phase. In particular, OC of BFW during the reproductive period increased more sharply compared to non-reproductive period when the increase of water temperature was accompanied by the shift from dark to light phase. This implies that they react to the light more sensitively for reproductive period than for non-reproductive period.