For many years, people fishing along the Anacostia River in Washington, D.C., noticed that brown bullheads often had red, fleshy bumps along their lips. Credit: USFWS

Solving the riddle of skin tumors in brown bullhead catfish

The Problem and Effects:
Scientists and environmental managers monitor bottom-dwelling fish, like brown bullhead catfish, for tumors because their health indicates the quality of the water and habitat. Bullhead catfish feed on worms, insect larvae and small crustaceans living in the mud. Because their food lives in the sediment, these fish are susceptible to the cancer-causing chemicals that accumulate there. As a result, these fish develop liver and skin tumors.

Carcinogens in sediments, especially polynuclear aromatic hydrocarbons (PAHs), are strongly linked to liver tumors. PAHs can are found in gasoline, oil, coal, car exhaust and road particles.

What We're Doing:
In 2005, a Chesapeake Bay Field Office study revealed an unexpectedly high rate of skin tumors (53 percent) in bullheads from the South River near Annapolis, Md. Twenty percent of these fish also had liver tumors. The river has no point sources for cancer-causing chemicals and is largely bordered by homes and buffered in many areas by woods. The study received considerable attention from local media and congressional representatives.

The Service developed a more intensive study to try to determine the causes of these tumors. In partnership with the U.S. Geological Survey, South River Federation, George Washington University Medical Center, Stockholm University, and Penn State University-Behrend Campus, the Service sampled the South River four more times, as well as the Severn, Rhode, and Choptank rivers.

The team found consistently high levels of skin tumors in the South River but few or no liver tumors in these collections. One collection of the Severn River had 52 percent with skin tumors but two others were lower (10 and 2 percent). The Choptank River was low in both types of tumors in two collections. The Rhode River had 6 percent of each type, but the sample size was small.

In addition to examining the fish for skin and liver tumors, the team looked at the DNA in the liver and skin tissues for PAHs and alkylating agents. Early in the cancer process, chemicals attached to DNA.

Neither the DNA nor the sediment data suggested an association between fish with tumors and exposure to PAHs or alkylating agents. Thus, though the team was able to rule out some causes, questions remain. Follow-up studies will examine the immune system of fish from some of the rivers to see why they frequently develop tumors.

A fact sheet is available on the CBFO Web site and a journal article, published recently in Science of the Total Environment is available from lead author Fred Pinkney.

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