I have a breeding group of shellies (N. multifasciatum) in a 10' long raceway. In addition to the shells, a couple terra cotta saucers left over from an experiment have pea gravel in them. Shells are at least 1' from the saucers. Still, the male shellies are moving the rocks. They are moving them more than 4'! Anyone have any ideas why the fish are doing this? I have seen one sunfish (Lepomis) species do similar and so not know why they do it either.