Tests conducted by officials at the New Jersey Department of Environmental Protection Division of Fish and Wildlife have determined that fish are dying because of a disease caused by a parasite.
“The necropsies determined that the shad that died in Lake Carnegie had a gill disease caused by the protozoan parasite, Ichthyophthirius multifiliis, also known as `Ich’,” DEP Spokesman Larry Hajna said. “Outbreaks with this parasite can occur in the spring, and it was likely initiated by stressors including warming water temperatures and the ease of transmission with the high densities of gizzard shad in the lake.”
The disease can infect a variety of fish species, Hajna said.
Scores of dead fish have been seen washed up on the shore and floating in the lake, as well as in the Millstone River, over the last few weeks. Residents who have lived near the lake for more than two decades have never seen a fish kill at the lake like this one.
Most of the fish are gizzard shad, but residents have also taken several photos of dead carp. Many of the dead shad have red blotches on their heads. Other fish can be seen in the river and lake gulping for oxygen. The fish range in size from a few inches long to about three feet long.
Gizzard shad are very sensitive to cold water temperatures and their inability to acclimate causes mortality at low temperatures. As water temperatures rise, populations of disease-causing organisms such as bacteria and parasites increase. Viruses can also kill fish. Experts say that diseases in lakes seldom kill all the fish, and are likely to affect only one or two species.