The effect of the design of ultraviolet irradiation unit on disinfection performance and operating costs was investigated for aquaculture purposes. Two prototypes (H and U) were compared with a commercial UV filter (I). The water samples for microbiological cultivation were obtained from water inlet and outlet of three different types of UV units in four replicates at 15 degrees C and 25 degrees C of sea water temperatures. Finally, considering the efficiency of reduction the total heterotrophic bacterial load of the UV filters, although significant differences were not found statistically, the best results were obtained from U type UV chamber at both temperatures (15 degrees C and 25 degrees C) (P>0.05). Also, it was estimated that make 60% savings in renewal and operating costs can be possible with changing the design of UV chamber.