Respiration rate of adult pilchard Sardinops sagax in relation to temperature, voluntary swimming speed and feeding behaviour

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 +/- 0.055 mg O-2 g(-1) wet wt h(-1). Respiration rate increased exponentially with temperature, and the mean Q(10) over the temperature range 10 to 22 degrees C 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-feeding was the most energetically expensive activity state. Swimming speed was the primary determinant of respiration rate when filter-feeding, whereas swimming speed and feeding intensity 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 filter-feeder. Results presented here contrast with those for Cape anchovy Engraulis capensis, a species for which filter-feeding 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.