Recirculating Aquaculture Systems (RAS) represent a sophisticated aquaculture methodology that optimises water utilisation while sustaining environmental integrity. A critical parameter within RAS is the concentration of dissolved oxygen (DO), which significantly influences the growth and overall health of aquatic organisms. Nanobubble (NB) technology is expected to increase the effectiveness of oxygenation in aquaculture systems because NB can produce nanometre-sized oxygen bubbles with longer residence time. This study aims to model DO concentration in RAS by utilising nanobubble technology, to improve system stability and efficiency. The DO dynamics model developed uses a numerical approach to analyse the dynamic balance of DO between the increase and consumption of DO in a water body by considering factors such as mechanical aeration, water circulation, and the oxygen demand of organisms. In mechanical aeration using NB, in terms of volumetric mass transfer coefficient ( \({k}_{L}a\) ), it has an advantage over conventional aeration methods. The \({k}_{L}a\) value indicates how effectively oxygen can be transferred from the gas phase (air bubbles) to the liquid phase (water) in the system. One of the things that affects the value of \({k}_{L}a\) is the size of the bubbles formed, therefore the DO dynamic model equation is directly affected by the bubble size of the NB. In this study, it has been successfully proven that mechanical aeration using NB with a bubble size of 50–130 nm has a \({k}_{L}a\) value of 0.0649 s−1 compared to MB which reaches 0.00024 s−1 and 0.00026 s−1 with bubble sizes of 40 and 500 µm.