To determine whether the seaweed Saccharina japonica can effectively utilize dissolved nutrients from Sebastes schlegeli fish cultures, a laboratory experiment was conducted in a static system for 7 days at ESFRI, NFRDI in Korea. The experiment included an S. schlegeli monoculture system and an S. schlegeli-S. japonica IMTA system. Saccharina schlegeli density ($415{pm}24g$; mean${pm}$SE) remained the same in all treatments, whereas seaweed density varied across treatments of 0, 0.5, 1, 2, and 3 kg (control and T1-T4, respectively). During the experiment, nutrient ($NH_4^+$ and $PO_4^{3-}$) concentrations were measured at 24-h intervals. $NH_4^+$ concentration of the control group increased from $0.117{pm}0.021mg/L$ at the start of experiment to $5.836{pm}0.904mg/L$ at the end of experiment. $NH_4^+$ concentrations of each treatment were $3.004{pm}0.040$, $2.086{pm}0.133$, $1.642{pm}0.121$ and $0.775{pm}0.007mg/L$ in T1, T2, T3, and T4, respectively, at the end of experiment. The concentration of $PO_4^{3-}$ exhibited a similar trend to $NH_4^+$ concentration. $NH_4^+$ and $PO_4^{3-}$ concentrations significantly decreased with increased S. japonica thallus density each day (P<0.05). The nutrient removal efficiency (NRE) and nutrient uptake rate (NUR) showed different relationships with changes in thallus density; NRE increased but NUR decreased as thallus density increased. Based on measured concentrations of $NH_4^+$ and S. japonica weight, regression analysis defined the relationship between as an exponential function, $Y=3.8165e^{-0.505X}$ ($R^2$ = 0.9552). Our results demonstrated that S. japonica can function as an efficient component in IMTA with environmental and potentially economic benefits for fish hatcheries.