Larval development of Penaeus monodon from protozoea (PZ1) to postlarval stages is described on natural and commercially available artificial larval diets under controlled laboratory feed trials. Five species of live microalgae (Tetraselmis chuii, Chaetoceros calcitrans, Skeletonema costatum, Rhodomonas baltica and Pavlova lutheri) were evaluated in feed trials at seven (5-60 cells gl1) cell concentrations with protozoeal larval stages. Performance of five animal diets (rotifers, Mytilus eggs, Artemia nauplii, barnacle nauplii and crab eggs) were examined in feed trials from Mysis (Ml) to postlarvae (PL1). Best results for protozoeal stages were obtained on a combination diet T. chuii + R. baltica at 40 cells µl-', while results from mysis to postlarvae were best achieved on Artemia nauplii. Natural feeds are expensive, difficult to maintain in mass culture and often vary in nutritional value. Larval performance on ten leading brands of artificial larval diet marketed using different process technologies were evaluated in replicated feed trials, together with factors causing variability in larval growth and survival of P. monodon. It was found that nutrient leach loss from unstable artificial feeds in culture conditions increases levels of ammonia and nitrite beyond safe limits. Live microalgal species at 1000 cells µl1 added to culture water reduces these toxic levels. The role of microalgae in larval culture is also examined. To further improve larval growth and survival on artificial diets, proteins from different sources, lipid, vitamin and mineral levels were incorporated in microencapsulated feeds. As a result improvement in larval development to postlarval stage was achieved with feeds containing 60% soya + mussel protein, 5% lipid and 13.9% vitamin and mineral mix. Algal homogenates supplemented to encapsulated feeds produced larval growth and survival comparable to live feed controls. P. monodon larvae were grown to the juvenile prawn stage solely on Frippak feeds. Larval growth was comparable to growth achieved on live feed controls. This study forms a basis for further investigations into nutritional requirements of penaeid prawns.