The tropical spiny lobster, Panulirus ornatus, is a highly valued crustacean species with great potential for aquaculture.The wild populations of P.ornatus has already over exploited while grow-out of wild caught seed have been increasingly practiced in S.E.Asian countries.Despite in recent years, phyllosoma larvae of P.ornatus has been reared to puerulus stage in laboratory scale operations on diets based on Artemia and fresh feeds, it still has a long way to go before hatchery produced seed supplying commercial farming might become a reality.The lack of knowledge on larval nutrition requirements and absence of a suitable formulated diet has been attributed as one of the major hurdles for P.ornatus larval culture.The present study first determined the optimal dietary protein inclusion level for a moist pellet specially developed for phyllosoma of P.ornatus.Five experimental diets were formulated at crude protein (CP) level at 5, 10,15, 20 and 25%, respectively with fishmeal as the protein ingredient.Triplicates of 50 early phyllosoma larvae (initial weight: 3.9 ± 0.1 mg) per replicate for each dietary treatment were cultured in 25 L rearing tanks within a flow through system at 26±0.5℃ and feed ad libitum twice daily over 3 weeks.Using non-linear regression analyses based on larval survival, development, growth (SGR) and deformity data, the optimal dietary protein inclusion levels were identified as on average at 10.0±1.3% CP.Identifying the optimal protein inclusion level is the first step toward better understanding nutritional requirements and development of a formulated feed for larval rearing of P.ornatus.Since the digestive system of P.ornatus phyllosome is described as being rudimentary with a limited digestive capacity, the subsequent step of investigation assessed whether fishmeal pre-digestion might increase the efficiency of digestion and absorption of formulated diets across larval gut wall and hence, improve performance of P.ornatus phyllosoma.Two external pre-digestion methods, i.e.1) acid denaturation and 2) enzyme hydrolysis, were compared with untreated fishmeal as the control.Three iso-nitrogenous experimental diets were hence formulated at a same protein inclusion level of 10% using acid denatured fishmeal (DFM), enzyme hydrolysed fishmeal (HFM) and untreated fishmeal (CFM), respectively.Five replicates with 40 phyllosoma (initial weight 2.5 ± 0.0 mg) per replicate were set up for each diet treatment.The general larval culture procedure was similar to that of the protein inclusion experiment except that phyllosome were fed 3 times daily and experiment lasted for 5 weeks.The results showed that phyllosoma fed HFM diet had a significantly better growth than the CFM treatment and both HFM and DFM treatment had significant faster larval development compared to CFM (p<0.05) treatment.Observation on gut retention of diet showed that at 6.5 h post-feeding, phyllosoma fed the HFM diet had a significantly higher ranked score for diet retention in hepatopancreas and hindgut and a significantly lower hepatopancreas tubular contraction frequency as compared to that of DFM and CFM treatment.It confirmed that the HFM diet was retained in the gut for longer and implying that a greater time for nutrient absorption across larval gut wall.This appears to be the first report showing clear beneficial effects of using pre-digested fishmeal in formulating diets for crustacean larvae and suggests a good potential of enzyme hydrolysis as a fishmeal pre-treated method in improving nutritional value of formulated diets designed for early phyllosoma of P.ornatus.