Metabolic, behavioral, and locomotive effects of feeding in five cyprinids with different habitat preferences

Fish generally perform routine swimming behaviors during food digestion; thus, changes in swimming performance and adjustments to spontaneous behavior resulting from digestion can have important ecological significance for wild fishes. The effects of feeding on metabolism, spontaneous activity, fast-start escape movement, and critical swimming speed (U crit) were investigated in five cyprinids with different habitat preferences, specifically the Chinese crucian carp (Carassius auratus), common carp (Cyprinus carpio), black carp (Mylopharyngodon piceus), Chinese bream (Parabramis pekinensis), and qingbo (Spinibarbus sinensis). Generally, species in still water exhibited increased feeding metabolism, whereas species in flowing water showed higher spontaneous activity and locomotion performance. Digestion had no significant effects on either spontaneous activity or fast-start escape movement in the five cyprinids. These results could be due to the small meal sizes (approximately 2% body mass) and active foraging modes of cyprinids. The changes in aerobic swimming performance due to feeding were more complex. No effect of digestion on U crit was observed in crucian carp (still water, high feeding metabolism, and low U crit), common carp (widely distributed, high feeding metabolism, and high U crit), and qingbo (flowing water, low feeding metabolism, and high U crit), but digestion resulted in a significant decrease in the U crit of Chinese bream (moderate feeding metabolism but high U crit) and black carp (moderate feeding metabolism and low U crit), suggesting no connection between postprandial U crit changes and feeding metabolism (or between U crit and preferred habitat). The maximum metabolic rate (MMR) of common carp and crucian carp increased after feeding, whereas the corresponding values for the other three cyprinids remained the same. The oxygen uptake capacity appears to meet the oxygen demand of both aerobic swimming and digestion in common carp and crucian carp, whereas qingbo sacrifices digestion for locomotion, and black carp and Chinese bream sacrifice locomotion for digestion under postprandial swimming conditions. The locomotion-priority mode of qingbo is adaptive to its active foraging mode in the demanding swimming habitat of rapidly flowing water, whereas the high respiratory capacities of postprandial crucian carp and common carp and hence the maintenance of their aerobic swimming performances might be a by-product of natural selection for hypoxia tolerance rather than for swimming speed.