Laboratory experiments investigated the effect of temperature, voluntary swimming speed and feeding behaviour on the respiration rate of adult pilchard Sardinops sagax. Mean routine respiration was 0.178 i 0.055 mg O2 g-' wet wt h-' Respiration rate increased exponentially with temperature, and the mean QIo over the temperature range 10 to 22OC was 1.82 * 0.35. Significant linear relationships were established between respiration rate and voluntary swimming speed for non-feeding, filter-feeding and particulate-feeding activities. Particulate-feedlng was the most energetically expensive activity state. Swimming speed was the primary determinant of respiration rate when filterfeeding, whereas swimming speed and feedlng intens~ty were equally important in determining respiration rate when particulate-feeding. That filter-feeding is energetically cheaper than particulate-feeding for this species supports previous work suggesting that pilchard IS primarily a f~lter-feeder. Results presented here contrast with those for Cape anchovy Engrauljs capensis, a species for which filterfeeding is energetically more expensive than particulate-feeding. Possible reasons for this difference are discussed. Calculation of a mean RQ (respiratory quotient) of 0.955 * 0.099 for pilchard indicates that this species catabolises both protein and carbohydrate.