Aquacultural production of various fish and crustacean species is continuing to grow throughout the world at over 6% per year, and projected to continue expanding as the demand for seafood increases and harvests from wild stocks remain at or beyond maximum sustainable levels. The efficiency of producing various aquatic species is generally considered to be greater than that of terrestrial livestock, primarily due to efficient feed utilization and protein accretion per unit of energy consumed. There is considerable variation in dietary protein requirements of various fish and crustacean species as well as their ability to use protein and lipid for energy. This variation appears to be primarily related to natural feeding habits in which aquatic species are generally categorized as being herbivorous, omnivorous of carnivorous. This presentation will provide an overview of the protein and amino acid requirements of prominent freshwater omnivorous and carnivorous fish species such as the channel catfish (Ictalurus punctatus) and rainbow trout (Oncorhynchus mykiss). Those requirements will be compared and contrasted with that of the red drum (Sciaenops ocellatus), a marine carnivore, and the omnivorous common carp (Cyprinus carpio) of which colored varieties are produced for ornamental purposes. Specific emphasis will be placed on application of the ideal protein concept in formulating diets for these various species.