- Intensive recirculating aquaculture systems (RAS) produce high volumes of biosolid waste which is a potential source of pollution if not properly treated. A reduction in sludge-mass would therefore minimize the potential environmental hazard and economic burden stemming from its disposal. Recently, anaerobic digestion was suggested as an alternative to aquaculture sludge digestion and stabilization in RAS. This practice results not only in sludge-mass reduction, but also in water and energy savings, as well as in biogas production in certain practices, which can serve as an alternative energy source and partially cover the RAS's energy demands. In the current review, we summarize the reports on anaerobic digestion of sludge produced in RAS and compare the efficiencies of various methods.