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Abstract. Four practical diets containing crude protein (CP) at 40% with or without raw and heat-treated mung bean (Phaseolus aureus) seed meals were formulated to replace 30% of soybean meal (SBM) protein in the diets for juvenile sea bass ( initial body weight = 1.04 g) during a 60-day feeding trial. The basal diet formulation contained Peruvian fish meal, shrimp meal, squid meal with defatted soybean meal as the major plant protein source. Diet 1, the control (CTRL) contained 32% SBM; Diet 2 raw mung beans (RwMB) contained 22.40% SBM with 17.63% RwMB; Diet 3 boiled mung beans (BoMB) contained 22.40%SBM with 18.32% BoMB; and Diet 4 autoclaved mung beans (AcMB) contained 22.40% SBM with 18.38% AcMB. Fish of similar sizes were randomly distributed into twelve 100 L conical fiberglass tanks with filtered aerated seawater, and each tank was stocked with 15 fish per treatment at three replicates. The best growth response and feed conversion ratio (FCR) were observed with sea bass fed Diet 4 (8.45 ± 0.4 g; 2.02) followed by Diet 3 (8.33 ± 0.2 g; 2.06); Diet 1 (8.26 ± 0.3 g; 2.08) and Diet 2 (6.59 ± 0.2 g; 2.44) groups. Similar results were also obtained for specific growth rate (SGR) and protein efficiency ratio (PER). Diet 4 (AcMB), Diet 3 (BoMB) and Diet 1 (CTRL) groups had comparable SGR (1.50 - 1.52% day-1) and PER (2.02 - 2.08) values, but significantly (P < 0.05) higher than that of Diet 2, (RwMB) with SGR (1.34% day-1) and PER (1.02) values respectively. The whole body composition of sea bass fed the various diets was not significantly (P > 0.05) different from each other. During the experimental period, seawater temperature ranged from 26 - 29 0C, ph of 7.30 - 7.75, dissolved oxygen of 6.8 - 7.6mg L-1, salinity of 29 - 32 ppt, ammonia-nitrogen (NH3-N) of 0.02 - 0.035mg L-1 while nitrite-nitrogen (NO2-N) values ranged from 0.015 - 0.019mg L-1. Survival rate (86.67%) of fish was not significantly (P > 0.05) affected by the different dietary treatments. No pathological and nutritional deficiency signs were observed other than growth depression in fish fed raw mung bean (Diet 2) at the end of the feeding trial. In conclusion, under the experimental condition, the...