Lease, Hilary M., Histopathological Changes in Gills of Lost River Suckers (Deltistes luxatus) Exposed to Elevated Ammonia and Elevated pH, M.S., Department of Zoology and Physiology, December, 2000. The Lost River sucker {Deltistes luxatus) is a federally listed, endangered fish species endemic to Upper Klamath Lake?a large, shallow hypereutrophic lake in southern Oregon. Sucker population declines in the lake over the past few decades are thought to be partly attributable to extreme water quality conditions, including elevated ammonia concentrations and elevated pH, that occur during summer cyanobacterial blooms. I analyzed structural changes in gills of larval Lost River suckers after they were exposed to elevated pH and elevated ammonia concentrations in chronic toxicity tests conducted in the laboratory. Histopathological changes in sucker lamellae were observed at ammonia concentrations that did not significantly decrease survival, growth, whole-body ion content, or swimming performance. Structural changes that I evaluated included O2 diffusion distance, lamellar thickness, hyperplasic and hypertrophic mucous cells, and infiltration of white blood cells into the lymphatic space. The increases in diffusion distance and lamellar thickness were statistically significant (P < 0.05). These gill changes are indicative of potentially compromised respiratory and ionoregulatory capacity. Because in this species gill structural changes appear to be a more sensitive indicator of stress in eutrophic water quality conditions than are the more traditional sublethal indices, gill histopathology might be useful for monitoring the health of Lost River suckers in Upper Klamath Lake.
Thesis/dissertation; Includes bibliographical references (leaves 55-63)