Pebble nest microhabitats of Semotilus species (Pisces: Cyprinidae)

The pebble nest microhabitats of four species of Semotilus were compared. Pit/mound nests of Semotilus corporalis were significantly larger than the pit/ridge nests of Semotilus atromaculatus, Semotilus lumbee, and Semotilus thoreauianus. Nests of S. corporalis were in wider and deeper streams. Pits of S. lumbee nests were longest of the four species; those of S. corporalis were widest and deepest. Semotilus corporalis used a greater proportion of larger stones (23 mm or greater) in nest construction than the other three species. There was no significant difference in the electivity index (percentage of nest pebble sizes versus those of the substrate) among the species for the three largest stone sizes (6.0, 11.3, and 23.0 rom). Although the greatest percentage of stones in the nests of S. corporalis were 23 mm, they did not represent the greatest electivity index as that stone size was present in the greatest percentage in the substrate. Pebble nests mounds and ridges served as breakwaters, reducing the flow to near zero in the downstream pit below the ridge or mound of