Systematic habitat destruction over the last 100 years combined with major anthropogenic stressors such as aquatic contaminants, exotic species, and economic endeavors are driving the decline in freshwater unionid species diversity. Two hundred fifty-seven individual adult Texas pigtoe (Fusconaia askewi) mussels (mean length, mm ± 1 SD; 58.7 ± 13.8) were collected from the upper Sabine river near Hawkins, Texas and taken to the University of Texas at Tyler to evaluate three factors likely impacting mussels in East Texas: siltation (a surrogate for bank erosion), elevated temperature and nitrogen. The impact of siltation was evaluated by burying mussels at two depths (0.25 and 0.5 meters) with a control group placed on top of the sediment. Over a 96-hour test period the resulting mortality was 15% at 0.25 meters, and 35% at 0.5 meters, with 100% survival in the control group. In the thermal tolerance study 100% survival occurred at both the control (20°Ϲ) and the 25 °Ϲ test points. The 30°Ϲ treatment group had overall mortality of 14% and the 35°Ϲ treatment group showed a mortality rate of 43% by the end of the trial. Treatment groups for nitrogen exposure were 0, 6.25, 12.5, 25, 50, and 100 mg/L total ammonia nitrogen (TAN). Mortality resulting from nitrogen toxicity was 50% at 50.0 mg-N/L and 100% at 100 mg-N/L. There was also a significant effect of nitrogen concentration on tissue glycogen levels [F (5, 44) = 3.370, p = 0.012]. Behavioral changes in burrowing and gaping were noted in response to pollutant stress, though they were not significantly different than control mussels [F (1, 10) = 2.966, p = 0.1158], [F (1, 10) = 3.193, p = 0.076].

Date of publication

Summer 8-9-2018

Document Type




Persistent identifier


Committee members

Lance Williams, Ph.D., Neil Ford, Ph.D., Brent Bill, Ph. D., Marsha Williams, MS.


Master of Science in Biology