Limited water exchange production systems for freshwater ornamental fish

Two biofilter designs and a control were tested in triplicate to determine if inexpensive bioremediation devices could increase production and decrease water use on ornamental fish farms in Hawaii. Koi (Cyprinus carpio L.) were used as the model species and the experiment was conducted outdoors in greenwater. When fish density was 9.7 kg per 2.08 m(3) and they were eating 125 g day(-1), the 20 L trickle filters were able to maintain acceptable water quality Tanks with the same size submerged filters suffered significantly lower dissolved oxygen levels compared with tanks with trickle filters and control tanks with no biofilters exhibited significantly higher nitrite-nitrogen (about 20 mg L-1) and nitrate levels (about 400 mg L-1). As typical ornamental fish weigh 3 g, the trickle biofilter system described here can produce 1.55 fish L-1 (compared with the industry standard 0.25 fish L-1) and use very little water other than the water originally in the tanks.