To investigate the effects of digestion on swimming performance and maximum metabolism of fish with different meal sizes, the constant acceleration test speed (Ucat) and maximum metabolic rate (MMR) were measured in juvenile fish of six species at a water temperature of 25 ℃. The six species studied were: Ictalurus punctatus and Clarias gariepinus (the order Siluriformes); Barbus capito and Mylopharyngodon piceus (the order Cypriniformes); and Sciaenochromis fryeri and Chindongo socolofi ‘albino’ (the order Perciformes). Measurements were taken under two states: the fasting state (control group) and post-prandial state (fed group). The results showed that: 1) At the interspecific level, the Ucat of C. gariepinus and M. piceus was lower than that of the other four species during digestion, and the difference was statistically significant (p<0.05); at the intraspecies level, the Ucat of I. punctatus and C. gariepinus in the fed group decreased significantly compared with the control group (p < 0.05). 2) At the interspecific level, the MMR of C. gariepinus was lower than that of the remaining five species during digestion, and the difference was statistically significant (p<0.05); at the intraspecies level, there was no significant difference in MMR between the fed and the control groups of the six fish species. 3) There was no statistically significant correlation between meal size and the rate of change in Ucat and MMR. The results suggest that the differences in the effects of digestion on the swimming performance and maximum metabolic rate of fish with different meal sizes may stem from differences in habitat conditions, digestive capabilities, feeding metabolic rates and metabolic strategies among different fish species.