Threonine is typically the third limiting amino acid in plant-protein based diets and its deficiency leads to poor production performance and health of farmed fish. Production of l argemouth bass (LMB) for food-fish markets has increased but information on its amino acid requirements remains limited. The objective of this 8-week feeding trials was to assess the dietary threonine requirement of LMB.
A semi-purified basal (Basal) diet was formulated to contain 40% crude protein (CP) , 12% lipid , and 0.65 g/100 L-threonine (Thr) . Crystalline L-Thr was supplemented to the Basal diet in additive amounts of 0.15 g/100g originating six additional diets w ith total Thr ranging from 0.65 to 1.5 g/100g. Each diet was fed twice daily to apparent satiation to triplicate groups of 20 LMB juveniles (6.6 g/fish initial weight) stocked in 110-L glass aquaria operating as a recirculating system. Water quality was kept within acceptable ranges for LMB and a 12h photoperiod was maintained by timer-controlled fluorescent lights .
Mean s urvival of LMB ranged from 72% (Basal diet) to 94% (remaining treatments). A four-parameter saturation kinetics model was used to fit the resulting data . The total dietary Thr requirement supporting 95% of maximum final weight and feed efficiency ratio (FER) of LMB was estimated to be approximately 0.88 g/100g (Figure) , corresponding to 2.14 g/100 of dietary CP, respectively. Additional results including Thr and protein retention efficiencies of LMB will be presented. The dietary Thr requirement values determined in this study will aid in the formulation of nutritionally balanced and cost-effective diets for LMB.