Technical Abstract: Aquaculture methods for queen conch, Strombus gigas, have been established for several decades. However, there is a need to improve husbandry techniques for the growout of juveniles. The purpose of this study was to determine growth and survival of juvenile queen conch fed artificial diets with increasing levels of the red algae Agardhiella species. The Rodophyta Agardhiella sp., soy protein isolate, and fish oil were increased at the expense of catfish feed and/or wheat flour to maintain the diets isonitrogenous (38% crude protein) with increasing protein to energy (P:E) ratios (83 – 96 mg CP/kcal). Yttrium was also incorporated as an inert marker for determining digestibility of dietary nutrients. Juvenile queen conch were stocked at 75 conch/m2 for a total of 16 conch per replicate (three replicates), and were fed 125 mg of diet per conch each day for six months. Dietary crude protein ranged from 31 to 38%. Dietary lipid, moisture, energy, ash, fiber, carbohydrate, and yttrium in each diet were also determined. Juvenile conch were measured (shell length and wet weight) every six weeks. At the end of the experiment, feces were collected to determine protein, energy, and dry matter digestibility. Results indicated the highest growth rates (0.10 mm/d and 0.11 mm/d) and survival were for the conch fed diets with a soy protein isolate protein substitution of 15% or less. This study highlights the importance of the protein source in the artificial diets of juvenile queen conch.