Cage cultured Nile tilapia, Oreochromis niloticus, were sampled at a commercial set-up on two occasions in 1995 in Laguna de Bay, Philippines, each time over a 24 h cycle. The stomach content weights were averaged for each subsample and analysed with the computer model MAXIMS. The model predicted that, in May, larger fish (mean total weight: 31.5 g) feeding on natural food alone fed continuously from dawn to dusk, ingesting 5.1 % body mass equivalent (% BME, wet weight basis) whereas smaller fish (mean total weight: 9.8 g) had two feeding periods per day, from sunrise to mid-morning and again from mid-afternoon until after sunset, ingesting 13.7 % BME. In August, fish were given supplemental feed once daily at 07:00 h. These fish (mean total weight: 81.7 g) fed intensely until supplemental feed ran out before mid-day, after which some ingestion of natural food took place later in the day. The fish ingested 5.8 % BME supplemental feed and 5.1 % BME natural food per 24 h. In May, most of the stomach contents consisted of the blue-green alga Anabaena spiroides, whereas in August, the natural food was made up principally of detritus.