The effects of caudal fin loss and regeneration on the swimming performance of three cyprinid fish with different swimming capacities

Abstract

Summary In nature, the caudal fins of fish species are frequently lost to some extent by aggressive behaviour, predation and diseases. To test whether the swimming performance of fish with different swimming capacities would be differentially affected due to caudal fin loss and regeneration, we investigated the critical swimming speed (Ucrit), the swimming metabolic rate (MO2), the tail beat frequency (TBF) and the tail beat amplitude (TBA) after caudal fin loss and regeneration (20 days) in juveniles of three cyprinid fish species: the qingbo (Spinibarbus sinensis) (strong swimmer), the common carp (Cyprinus carpio) (intermediate) and the goldfish (Carassius auratus) (poor swimmer). The Ucrits of the caudal-fin-lost qingbo, common carp and goldfish were 49%, 32% and 35% significantly lower than those of the control groups, respectively. The maximum tail beat amplitude (TBAmax) (all three fishes), the maximum tail beat frequency (TBFmax) (only the common carp and the goldfish) and/or the active metabolic rate (MO2active) (only the common carp) of the caudal-fin-lost fish were significantly higher than those of the control groups. After 20 days of recovery, the caudal fins recovered to 41%, 47% and 24% of those of the control groups for the qingbo, the common carp and the goldfish, respectively. However, the Ucrit values of the fin-regenerated qingbo, common carp and goldfish recovered to 86%, 91% and 95% of those of the control group, respectively. The caudal-fin-regenerated qingbo and common carp showed a significantly higher TBAmax and TBFmax, respectively, compared with those of the control groups. The qingbo had a higher TBFmax but a lower TBAmax than the common carp and the goldfish, which suggested that a strong swimmer may maintain swimming speed primarily by maintaining a greater TBFmax, for which the caudal fin plays a more important role during swimming, than a poor swimmer. The MO2active of fish (common carp) with a redundant respiratory capacity could increase due to caudal fin loss to meet the increase in energy expenditure required by an increase in TBFmax. In addition, the sustain swimming performance may not be the only selective pressure acting on caudal fin size in the qingbo, the common carp and the goldfish and the present caudal fin size of these three fish species may be a trade-off between sustain swimming performance and other factors (e. g. sexual selection; escape responses).