Extract of a desert plant, Yucca scindigera (YUPE) at 0 mg L(-1) (control), 18.36 and 72 mg L(-1) was added to seawater containing 30, 50 and 100 Kuruma shrimp Marsupenaeus japonicus postlarvae (PL) per liter with or without aeration for 24 h to study its effects on reducing ammonia excreted from the PL. Even at the lowest YUPE addition level and the highest PL density, no ammonia accumulated in both aerated and noaerated set-ups for up to 12 h. Ammonia accumulated only in the controls. YUPE showed more effective in reducing ammonia in seawater from this biogenic source than ammonia from chemical source used in previous studies. Consequently. YUPE is identified as a natural, safe, and effective solution for ammonia reduction in seawater and mariculture. (C) 2010 Elsevier Ltd. All rights reserved.