9419167 Fish use special sensory organs called lateral line systems to detect water motion and pressure changes produced by underwater sounds. The sensory receptors, called neuromasts, are usually sheltered in canals but sometimes exposed on the surface. The canals are thought to filter low frequency noise, like that produced by water motion from stream flow or active swimming, and improve the ability of fish in noisy environments to detect signals produced by other swimming animals. Lake Baikal in Siberia is the world's deepest and oldest freshwater lake. Its fish fauna is dominated by sculpins which have evolved unusual lateral line systems that include mostly superficial neuromasts except for a few species with neuromasts primarily in canals. The abundance of species with mostly superficial neuromasts is a unique feature of this ancient lake, and provide a special opportunity for the study of canal function. The lake has 29 species of closely-related sculpins, most of which live in the quiet and dark depths, but some of which come to the surface to feed at night. This research will examine the search behavior and ability to detect prey of the Baikal sculpins, and test the hypothesis that sheltering neuromasts in canals is an adaptation to foraging in noisy environments. Fish responses to prey will be videotaped in noisy and quiet environments, and reaction distances will be used as an index to prey sensitivity. Anatomy of the lateral line organs will be documented using plastic casts of the canal systems and scanning electron microscopy to count hair cells. The research will determine the functional and adaptive significance of lateral line architecture. It may ultimately lead to an understanding of the design of canal structure in filtering noise and increasing sensitivity to certain underwater signals.
