Hybrid tilapias (Oreochromis niloticus x O. mossambicus) were studied to determine gastric emptying and gastrointestinal transit time. The fish were divided into two groups. All fish were fasted for 12 h. The first experiment consisted of 11 fish fed with commercial food pellets and then administration of barium sulfate directly into the stomach using a blunt-end needle. Fish were then radiographed at different time intervals. The second experiment consisted of eight fish, which were given only barium sulfate after 12 h of fasting. In the first experiment, the stomach emptied completely, ranging from 4 to 15h postcontrast medium administration, whereas the gastrointestinal transit time ranged between 10 and 26 h. As for the second experiment, the contrast medium was still retained in the stomach in 50% of the fish after 24 h. The study did not proceed beyond 24 h as fish were considered stressed after this period of time. Thus, no data for the gastrointestinal transit time was obtained.