Date of Graduation


Document Type


Degree Type



Davis College of Agriculture, Natural Resources and Design


Wildlife and Fisheries Resources

Committee Chair

Patricia Mazik

Committee Member

Vicki Blazer

Committee Member

Amy Welsh


Smallmouth bass (Micropterus dolomieu) are an important sportfish in the Susquehanna and Potomac River Basins of the Chesapeake Bay drainage. However, population declines in portions of the Susquehanna, fish kills and reports of visible abnormalities such as melanistic spots have raised concern among the public and resource managers. Although the etiology or risk factors associated with melanistic lesions are unknown, there is a propensity to attribute the abnormality to contaminants. Melanistic lesions of smallmouth bass were assessed using histopathology and gene expression analysis to evaluate the cellular and molecular changes compared to normal skin. The prevalence of melanistic bass at specific sites in the Chesapeake Bay drainage was also examined. Higher incidences of bass with melanistic lesions were documented in the Susquehanna River compared to the Potomac River. Typical melanistic lesions consisted of rounded to spindle shaped, melanin-containing cells (or melanophores) in a thickened epidermis whereas normal skin only contains melanophores in the dermal-epidermal interface. RNA-Seq data revealed the expression of a papillomavirus helicase exclusively in melanistic areas. Transcript abundance analyses of DCT (L-dopachrome tautomerase), MC5R (melanocortin receptor 5), MITF (micropthalmia-associated transcription factor), PMEL (melanocyte protein), TYR (tyrosinase), TYRP-1 (tyrosinase-related protein 1), Rab38 (Ras-related protein Rab-38), Akt1 (RAC-alpha serine threonine-kinase), KRT8 (keratin type II cytoskeletal 8), and MT-1 (metallothionein) showed differential expression in melanistic areas. Further research will be needed to determine the roles of a potentially novel papilloma virus and chemical contaminants in induction of melanistic areas of smallmouth bass.