Abstract: Complete ammonia oxidizing bacteria (comammox) can complete the entire nitrification process from ammonia nitrogen to nitrate within a single cell. They exhibited a high substrate affinity, microaerophilic preference, and slow–growing oligotrophic strategy, enabling rapid growth under conditions of low ammonia, low dissolved oxygen, and attached state. These ecophysiological characteristics conferred significant engineering application potential in recirculating aquaculture systems and various biofilm reactors. The selective enrichment of comammox can be achieved by extending cultivation time, establishing microaerophilic gradients, and employing high specific surface area carriers. This approach reduced aeration requirements, enhanced nitrification stability, and held promise for lowering greenhouse gas emissions. The current problems faced in the application and promotion mainly included limited salt tolerance, decreased activity at low temperatures, long time required for enrichment and amplification, as well as insufficient existing molecular detection tools. To advance its engineering applications, a standardized function test and flux assessment systems should be established. Cross–seasonal and large–scale demonstration pilots should be conducted. At the same time, nitrogen removal effect, greenhouse gas flux, energy consumption, and safety for aquatic animals should be evaluated. Thus, the ecological advantages can be transformed into scalable aquaculture engineering strategies.