Spawning Association of the Redfin Shiner, Notropis umbratilis, and the Green Sunfish, Lepomis cyanellus

The reproductive behavior of the redfin shiner, Notropis umbratilis, is described with emphasis on the spawning association between this species and the green sunfish, Lepomis cyanellus. Daily tabulations of the number of male redfin shiners present on the spawning grounds during 2 breeding seasons showed that more male shiners were present over the nests of green sunfish during times when sunfish were establishing nests and spawning than at any other time. Studies conducted in small areas of the spawning grounds also showed that dense aggregations of minnows formed over nests of actively spawning male green sunfish. Eggs collected on watch glasses placed in occupied and unoccupied sunfish nests indicated that redfin shiners utilized nests throughout the period they were occupied, but that they rarely used unoccupied nests. The following field experiments were conducted: removal of sunfish from their nests, establishment of moving sunfish models, visual occlusion of sunfish nests, and introduction of water containing milt or ovarian fluid of the green sunfish. When milt or ovarian fluid was released into a pond, shiners assembled and carried out breeding activities at the site where the fluid was added. Using this technique, spawning aggregations of shiners were produced over a muck substrate in the absence of both green sunfish and nests. Shiners also collected over a moving model of a sunfish; they showed no reproductive behavior and left as soon as the movement of the model ceased. Male shiners continued to defend their territories when nests were occluded, but the removal of sunfish resulted in a marked decrease in the number of shiners defending territories. An odor hypothesis is presented to explain the mechanism involved in the use of sunfish nests by Notropis umbratilis. It is suggested that the scent of milt and ovarian fluid by spawning sunfish initially attracted the shiners to the sunfish nest and sexually stimulated them. On subsequent days, some of these male shiners returned to the sunfish nest and continued their reproductive activities.