A recirculation aquaculture system (RAS) is a type of aquaculture system that recycles and filters water, rather than relying on a constant flow of fresh water or exchanging water with the environment. The goal of a RAS is to create a closed-loop environment that can efficiently maintain optimal water quality, temperature, and oxygen levels for the cultivation of aquatic organisms.

In a RAS, water is filtered and treated to remove waste products and excess nutrients, and then recirculated back into the system. This allows for a high degree of control over the water quality and environment, which can help to reduce the risk of disease, improve the health and growth of the cultured organisms, and reduce the overall water and energy consumption of the system.

RAS are commonly used for the cultivation of species such as finfish, shellfish, and crustaceans, and are particularly useful for the culture of species that require precise water quality conditions. They can be designed for a wide range of scales, from small-scale systems for home or hobby use to large-scale commercial systems.