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

Pericarditis in Johnny Darters

Many wild caught Johnny Darters have pericarditis, and some have trematode parasites in the pericardial sac. The natural parasite assemblages of Johnny Darters have not been well described, nor have cases of natural pericarditis been well described in fish, so this an exciting opportunity to identify and fully characterize parasites and associated disease.

research project

Toxicity of antilipidemic drugs in fish embryos

Wastewater treatment plants discharge a mix of drugs and pollutants that can impact the physiology of aquatic organisms. In partnership with CPW, a study of zebrafish and fathead minnow larvae exposed to antilipidemics showed dose responsive mortality and numerous deleterious effects. This project precisely demonstrates the connections of human, environmental, and animal health (One Health).

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.


Branchitis and mortality in rainbow trout Oncorhynchus mykiss exposed to iron oxidizing bacteria: diagnostics and management in a Colorado hatchery.
Clift AK, Malmlov AM, Wells CL, Cadmus P, Schaffer PA .
Aqua. Fish & Fisheries. 2022 Mar;00:1–6.

Morbidity and mortality in Danio rerio and Pimephales promelas exposed to antilipidemic drug mixtures (fibrates and statins) during embryogenesis: Comprehensive assessment via ante and post mortem endpoints.
Kingcade A, Ahuja N, Jefferson A, Schaffer PA, Ryschon H, Cadmus P, Garrity D, Ramsdell H.
Chemosphere. 2021 Jan;263:127911. doi: 10.1016/j.chemosphere.2020.127911. Epub 2020 Aug 30. PMID: 33297010

Meningoencephalitis associated with Carnobacterium maltaromaticum-like bacteria in stranded juvenile salmon sharks (Lamna ditropis).
Schaffer PA, Lifland B, Van Sommeran S, Casper DR, Davis CR.
Vet Pathol. 2013 May;50(3):412-7. doi: 10.1177/0300985812441033. Epub 2012 Mar 27. PMID: 22452824

Delayed diagnosis of fatal pneumonic canine plague: clinical and pathologic features in two naturally infected Colorado dogs.
Schaffer PA, Hershkowitz CS, Dowers KL, Golchanour JL, Harris LJ, Aboellial TA, Morley PS, Brault SA, Pabilonia KL, Mason GL, House JA, Daniels JB.
BMC Vet Res. 2020 May 25;16(1):160. doi: 10.1186/s12917-020-02361-z. PMID: 32450913

Acanthomatous ameloblastoma with atypical foci in five dogs.
Malmberg JL, Howerth EW, Powers BE, Schaffer PA.
J Vet Diagn Invest. 2017 Mar;29(2):154-159. doi: 10.1177/1040638716682565. Epub 2017 Feb 8. PMID: 28176614

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