GILL DISEASE: Gizzard shad from Lake Carnegie that were necropsied last week by the NJ Department of Environmental Protection Division of Fish and Wildlife were found to have a gill disease caused by a common protozoan parasite. (Photo Courtesy of Division of Fish & Wildlife)

The spring die-off of hundreds of gizzard shad in Lake Carnegie, noted by many residents over the past couple of weeks, is the result of a gill disease caused by a parasite known as “Ich” (Ichthyophthirius multifiliis), according to a pathology report issued Saturday by the NJ Department of Environmental Protection Division of Fish and Wildlife (F&W).

Outbreaks of Ich occur most commonly in the spring, and significant die-offs of gizzard shad are most often a result of a stressed fish population and warmer water temperatures that favor parasite proliferation. “Gizzard shad are cold-blooded and particularly sensitive to warming water temperatures,” commented Jan Lovy, F&W research scientist in fish pathology and author of the report.

Noting that the proliferation of gizzard shad has become problematic in Lake Carnegie, Mr. Lovy said that this spring kill “did not significantly impact the population of gizzard shad, who have really exploded in that lake.”

Dead fish in Lake Carnegie, mainly gizzard shad from four to six inches long, were reported between April 12 and April 20, and on April 21 F&W netted, euthanized and transported ten young fish with lethargic behavior to the Pequest Fish Pathology Laboratory for necropsy.

According to Mr. Lovy’s report, Ich is a protozoan parasite ”found world-wide in a variety of freshwater fish species …. In this instance infection occurred mainly within the gills of the fish.”

The report concluded, “Dense fish populations are also known to favor transmission of infectious agents, including this parasite. The heavy fish densities in the lake combined with the water temperature stress most likely favored parasite infection and transmission, leading to this epizootic [epidemic].”

Mr. Lovy added that the gizzard shad were probably suffering from a problem of “over-wintering,” which weakened their immune systems as temperatures warmed. “We see these die-offs annually,” he observed, suggesting little cause for concern about involvement of environmental factors.