Technical Abstract: Two separate 8 week feeding trials were conducted to examine the impacts of fish meal replacement with an organically certifiable yeast-based protein source with and without supplementation of methionine, tryptophan, and taurine to diets for juvenile cobia. In the first trial, diets were formulated to contain 41% crude protein and 13% lipid, and a yeast-based protein replaced fish meal at 50 and 75% of dietary protein with and without supplemental taurine at 0.5 g/100 g dry diet. The control diet contained 100% herring fish meal. Methionine and tryptophan were added to all diets except the control to resemble the amino acid profile of fish meal. Results from this study indicated that fish fed diets supplemented with taurine exhibited significantly higher weight gain and better feed efficiencies than all other fish. Diet significantly impacted biological indices such as muscle ratio (MR), visceral somatic index (VSI), and hepatosomatic index (HSI). The 75% yeast-based protein diet without taurine returned the lowest MR values and the highest VSI and HSI values. In the second trial, diets were formulated to contain 43% crude protein and 11% lipid, with the control diet containing 100% herring fish meal and the same yeast-based protein replacing fish meal at 50, 75, and 100% of dietary protein. All diets except the control were supplemented with taurine at 0.5 g/100 g dry diet. Results from this study indicated that increasing amount of yeast-based protein led to decreased weight gains and feed efficiencies regardless of taurine supplementation. However, weight gain and feed efficiencies did increase when compared to a previous study [Lunger, A.N., McLean, E., Craig, S.R., 2007. The effects of organic protein supplementation upon growth, feed conversion and texture quality parameters in juvenile cobia (Rachycentron canadum). Aquaculture 264, 342¿352] using identical diet formulations except for taurine supplementation. MR values tended to decrease while VSI and HSI values tended to increase with increasing fish meal replacement. It is obvious from the results from both of the present studies that taurine supplementation does have a significant impact on growth and feed efficiency of juvenile cobia when they are fed diets containing high levels of plant-based proteins as replacements for fish meal. Additionally, alternate proteins, especially those of plant and yeast-based origin can be incorporated at very high levels in diets for cobia with proper amino acid supplementation.