Fisheries, Midwest Region
Conserving America's Fisheries

Tissue Collection
Tissue Collection

Introduction to Fish Health Course
Introduction to Fish Health Course


Reducing the Spread of Fish Pathogens

Like all animals, fish are susceptible to a variety of environmental, nutritional, and infectious diseases. If left untreated, these diseases can often lead to death. Infectious diseases, those caused by pathogens—organisms such as parasites, bacteria, or viruses— are of special concern because they can be easily spread to other fish within a hatchery, to another hatchery during fish transfers, or to wild populations if infected fish are released.

One or more pathogens may be present in a fish population without causing disease. However, placing a fish into a stressful situation can lower their resistance to disease, leading to an outbreak. Situations stressful to fish are common in the fish hatchery environment, including fluctuating water temperature, changes in water quality, overcrowding, handling, and transport. While fish can handle these stresses to a degree, prolonged stressful conditions may lead to an outbreak. Fish health center staff work hatchery personnel to decrease stressful conditions in order to prevent disease outbreaks from occurring. If a pathogen has been detected, or an outbreak occurs, fish health center personnel may recommend treatments such as vaccines, antibiotics, or chemotheraputants.

Fish Health Inspections

As its primary responsibility, the La Crosse FHC conducts fish health inspections at each of the six national fish hatcheries in the Midwest Region twice annually. The inspections serve as a method for early detection of pathogens and help to ensure that pathogens are not present before fish are transferred to another hatchery or released into the wild. The center also conducts once-annual inspections at four tribal fish hatcheries located in Michigan, Minnesota, and Wisconsin.

To conduct a fish health inspection, staff from the La Crosse Fish Health Center travel to the fish hatchery being inspected to observe the fish for any indication that disease is present, and to collect various tissue samples from fish at the hatchery. Tissue samples collected during the on-site aspect of the inspection. The tissue samples are transported back to the Center’s laboratory in Onalaska, Wisconsin where they are screened for viral, bacterial, and parasitic fish pathogens. Upon completion of the laboratory work, each hatchery receives an inspection report that lists what pathogens, if any, were found.

Diagnostic Cases

Occasionally, fish at a hatchery will begin to show signs of disease. When such an event occurs, biologists at the hatchery will contact the La Crosse FHC to discuss their observations and to make arrangements to send live fish to the fish health center for diagnosis. Using the information obtained from the hatchery staff, their own observations, and laboratory test results, biologists at the La Crosse FHC are able to make a diagnosis and recommend a plan of action to control or limit the outbreak. Recommendations may include treatment with antibiotics, chemotheraputants, or changes in practices at the hatchery.

Wild Fish Health Survey

While it is not possible to eliminate pathogens from the wild, knowledge of where pathogens exist in the wild can serve as a valuable tool for fishery managers. The La Crosse Fish Health Center, along with the Service’s other eight fish health centers, began the Wild Fish Health Survey in 1997 to gather this information. Working closely with fishery management biologists from state, tribal, and federal agencies, the La Crosse FHC selects sites and species of management importance to sample for the survey. The survey uses standardized procedures to screen for select bacterial, viral, and parasitic pathogens. Results for the National Wild Fish Health Survey from the La Crosse Fish Health Center and the other eight fish health centers can be found at:

Last updated: August 21, 2014