Data from: An interspecific comparison between morphology and swimming performance in cyprinids

Flow regimes are believed to be of major evolutionary significance in
fish. The flow regimes inhabited by cyprinids vary extensively from still
flow regimes to riptide flow regimes. To test (1) whether flow-driven
swimming performance and relevant morphological differentiation are
present among fish species and (2) whether evolutionary shifts between
high-flow and low-flow habitats in cyprinids are associated with
evolutionary tradeoffs in locomotor performance, we obtained data on both
steady and unsteady swimming performance and external body shape for 19
species of cyprinids that typically occur different flow regimes (still,
intermediate and riptide). We also measured the routine energy expenditure
(RMR) and maximum metabolic rate (MMR) and calculated the optimal swimming
speed. Our results showed that fish species from riptide groups tend to
have a higher critical swimming speed (Ucrit), maximum linear velocity
(Vmax) and fineness ratio (FR) than fish from the other two groups.
However, there was no correlation between the reconstructed changes in the
steady and unsteady swimming performance of the 19 species. According to
the phylogenetically independent contrast (PIC) method, the Ucrit was
actively correlated with the MMR. These results indicated that selection
will favour both higher steady and unsteady swimming performance and a
more streamlined body shape in environments with high water velocities.
The results suggested that steady swimming performance was more sensitive
to the flow regime and that for this reason, changes in body shape
resulted more from selective pressure on steady swimming performance than
on unsteady swimming performance. No evolutionary tradeoff was observed
between steady and unsteady swimming performance, although Ucrit and MMR
were found to have coevolved. However, a further analysis within each
typically occur habitat group suggested that the tradeoff that may exist
between steady and unsteady swimming performance may be concealed by the
effect of habitat.