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For Release: Friday, April 6, 2018

DEC: Cold Temperature Stress in Late Winter Causes Cyclical Fish Die-Off in Local Waterbodies

Large numbers of dead and dying fish have been observed in area waters including Irondequoit Bay and the Erie Canal in Newark, New York State Department of Environmental Conservation (DEC) reported today. Inspections by DEC Aquatic Biologists indicate that nearly all of the dead and dying fish observed are gizzard shad, a medium-sized member of the herring family.

Mortality of gizzard shad in late winter and early spring is common. The species is very sensitive to cold water temperatures and their inability to acclimate causes mortality at low temperatures. Gizzard shad are living near the northern edge of their range in the Great Lakes, making them especially susceptible to cold temperatures.

On March 27, DEC collected and submitted a sample of gizzard shad from Irondequoit Bay and sent them to Cornell University's pathology laboratory for disease screening. No viable samples were available from the Erie Canal. Results indicate the fish had a low level infection of viral hemorrhagic septicemia (VHS). VHS has been the cause of a disease issue in the Great Lakes region of the United States and Canada. VHS virus is a rhabdovirus (rod shaped virus) that affects fish of all size and age ranges. VHS can cause hemorrhaging of fish tissue. Once a fish is infected with VHS, there is no known cure. Not all infected fish develop the disease, but they can carry and spread the disease to other fish. VHS does not pose any threat to human health. Additional information about VHS is available on DEC's website at

Gizzard shad live near the northern edge of their range in the Great Lakes, making them especially susceptible to cold temperatures. Mild winters may have allowed their population to increase the last two years. Because the gizzard shad mortality is widespread and primarily affects one species of fish, their die-off is not considered an indicator of an environmental problem such as pollution. Mortality of a single species of fish suggests that the die-off is the result of a disease, parasite or species-specific stressor. In this particular case, late winter cold stress is the suspected cause.
Additional information about gizzard shad, including images, is available on DEC's website at

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