Schaffer Lab

My research niche melds fish pathology with diagnostics in aquaculture and uses pathology to investigate human impacts on native aquatic environments. I additionally enjoy all sorts of collaborations in domestic diagnostic veterinary pathology such as infectious disease, oncology, and radiology.

research project

Thermal stress on Johnny Darters (Etheostoma nigrum)

Wastewater treatment plant effluent can be much warmer than the surface water it is discharged into and can create gradients of thermal stress for aquatic animals, especially in winter months. In partnership with Colorado Parks and Wildlife and the CSU Cooperative Fish and Wildlife Research unit we have studied the effect of thermal influences on Johnny Darter reproduction above and below WWTP.

research project

First detection of sinoatrial Contracaecum in threatened Plains Topminnow

A recent histologic survey identified a unique and enormous nematode parasite inside the heart of ~30% of fish. This was identified as Contracaecum, and the Plains Topminnow represents a new host record for this parasite. We are working to better characterize the pathology of infection and impact on cardiac function and survival.

research project

Lateral line toxicology

There are many pollutants that are toxic to the lateral line, a key sensory structure that allows fish to feel vibrations and movement in the water column. The lateral line is critical to behaviors like foraging, schooling, and predator evasion. CPW and I are testing new methods to detect lateral line toxicity and the potential impacts on survival.

research project

Iron-oxidizing bacteria in a CPW Colorado hatchery

Iron-oxidizing bacteria (FeOB) colonized a groundwater well at a CPW trout hatchery and were associated with severe proliferative branchitis and high morbidity and mortality. This is the first report of morbidity and mortality in fish associated with FeOB. Further work includes speciation of the specific bacteria involved and genetic analysis for potential virulence factors.

research project

Vasculitis in Greenback Native trout

The Greenback native trout is Colorado’s state fish. This subspecies was thought to be extinct in the 1930s but an isolated population was found in the wild in 1957 and the fish population has been grown through breeding programs. Morbidity and mortality are issues in the culture setting, and we are investigating the cause of severe vasculitis that was identified in 3-month-old moribund fish.

Publications

A retrospective review of the histologic features and prognosis of hypercellular canine peripheral odontogenic fibromas.
Gross CC, Curtis BE, Hilty SR, McDonald CM, Schaffer PA, Frank CB. Vet Pathol. 2025 Oct 18:3009858251382165. doi: 10.1177/03009858251382165. Epub ahead of print. PMID: 41108520.

Sinoatrial Contracaeciasis in Johnny Darters (Etheostoma nigrum) and Plains Topminnow (Fundulus sciadicus) From the South Platte Drainage, Colorado
Schaffer, P.A., McGrew, A.K., Henley, J., Adams, C.M., Winkelman, D.L., Fitzpatrick, R.M. and Cadmus, P. (2025). Aqua. Fish & Fisheries, 5: e70100. https://doi.org/10.1002/aff2.70100

Histological progression and bacterial load dynamics of Renibacterium salmoninarum in Chinook salmon Oncorhynchus tshawytscha.
Dils RE, Firestone TBR, Schaffer PA, Winkelman DL, Fetherman ER. Dis Aquat Organ. 2025 May 22;162:85-97. doi: 10.3354/dao03852. PMID: 40401534

Epizootic of Clinostomum marginatum (Trematoda: Clinostomidae) in Ambystoma tigrinum from Colorado, USA: Investigation through Genomics, Histopathology, and Noninvasive Imagery.
Calhoun DM, Groves J, Schaffer PA, Achatz TJ, Greiman SE, Johnson PTJ. J Wildl Dis. 2025 Mar 20. doi: 10.7589/JWD-D-24-00068. Online ahead of print.PMID: 40107297

Environmental risk factors for UV-induced cutaneous neoplasia in horses: A GIS approach.
Ramirez M, Duncan C, Schaffer PA, Wobeser B, Magzamen S. Can Vet J. 2023 Oct;64(10):971-975. PMID: 37780476

more publications

People

Paula Schaffer Headshot
Paula Schaffer, D.V.M., M.S., DACVP

Associate Professor

news and updates view all

November 6, 2025 A discovery from the heart: Parasitic worms uncovered in native Colorado fish

MIP Associate Professor Paula Schaffer, in a cross-campus collaboration with Dana Winkelman in the Department of Fish, Wildlife and Conservation Biology, discovered a parasitic worm in the hearts of two native Colorado fish.
June 23, 2025 Paula Schaffer honored with inaugural CPW Aquatic Research Distinguished Service Award

She was honored for her technical expertise and government service in supporting the health of freshwater fish, amphibians and aquatic vertebrates.
November 13, 2023 MIP faculty & resident recognized for making a difference in veterinary pathology

Anatomic pathologist and MIP associate professor Paula Schaffer was honored with the ACVP Mentor of the Year Award at their national meeting, Oct. 28-30, 2023, in Chicago, Illinois.