Three species of freshwater algae (Spirulina platensis, Euglena gracilis and Chlorella vulgaris) labeled with 1 4 C were fed to larval tilapia (Oreochromis niloticus) with a standard length (SL) from 0.8 to 3.4 cm. This was conducted to clarify the acceptability of the three species of algae to developing larval tilapia based on their ingestion and assimilation of the 1 4 C-labeled algae. Ingestion rate (IR, μg C/fish/h) and assimilation rate (AR, μg C/fish/h), as well as ingestion efficiency (IE, %) and assimilation efficiency (AE, %) were investigated by monitoring the fate of the labeled food. Larval tilapia could ingest 2.6-85% of the available S. platensis biomass with larvae growing from an SL of 0.8-3.4 cm, and the relationship between IR and body weight (BW, mg) was expressed as IR=15.62BW 0 . 6 8 6 (r 2 =0.94). Larval tilapia ingested significantly less E. gracilis (1.6-26% of the available Euglena biomass) than Spirulina, and the relationship between IR and BW was IR=13.70BW 0 . 5 8 4 (r 2 =0.93). In contrast, a negligible amount (1.6-20% of the available C. vulgaris biomass) of Chlorella was ingested by larval tilapia over the range of sizes studied. For all three algae, a relatively lower assimilation efficiency (AE) was found in larvae right after the onset of exogenous feeding, but AE improved rapidly with increasing larval size from 0.8 to 1.2 cm SL. Spirulina was more readily assimilated (61.4-80%) than Euglena and Chlorella. Assimilated carbon from Euglena and Spirulina were about 1-2 and 3-6 times that of the resting carbon consumption requirement for respiration of the larval tilapia. It was concluded that Spirulina is more acceptable than Euglena and Chlorella as a diet for larval tilapia from the onset of exogenous feeding.