The water in the aquarium prior to usage was aerated for 1 week to dissolve oxygen in the water. Tilapia was stocked in each aquarium with the same density of 20 fishes per aquarium (average 20 g), sizes ranging from 9 to 10 cm. Fishes were acclimatized for 1 week before usage, in order to accumulate fish waste to enable the supply of nutrients for romaine lettuce. Fishes were maintained for 35 days and fed with pellet (commercial feed) as much as 3 % of body weight with 40 % feed protein content, three times a day (morning, noon, and afternoon). Water samples were taken every week. There was no water replacement during the experiment, except for the addition to replace the water lost due to evaporation.