Previously unknown virus linked to fish deaths

A new type of virus has been linked with a die-off of largemouth bass in Pine Lake, Wisconsin, U.S. This forms part of an investigation into a series of unexplained fish deaths last year.

The previously unknown virus was detected at the U.S. Fish and Wildlife Service's La Crosse Fish Health Center. The virus was isolated from dead fish that were collected and sent for analysis. During May 2015 a series of unexplained fish deaths occurred and the results of the analysis, centered on the discovery of the new virus, have been reported.

The new virus was detected by Professor by Tony Goldberg, who works out of the Pathobiological Sciences unit at the University of Wisconsin-Madison's School of Veterinary Medicine. The virus was detected through the use of advanced genetic sequencing methods. These involved sequencing millions of molecules from single samples. The outcome of this laboratory exercise was compared against known viral sequences. Here the fish-killing virus did not match a new type of virus was declared.

The new virus has initially been called “largemouth bass reovirus.” The virus has some similarity to other types of viruses known to be capable of killing fish. The major fish killing virus in recent years has been hemorrhagic septicemia virus. This virus has been found in lakes Michigan, Winnebago and Superior, and it affects musky, pike, bass, panfish and trout.

Initially it was assumed the bass had been killed by the hemorrhagic septicemia virus; the new analysis, however, suggests this is not the case. Here Professor Goldberg notes:  This family of viruses are emerging pathogens that infect all sorts of animals. They cause kills in marine and freshwater fisheries, including in wild and farmed populations."

Whether the new virus is solely responsible for the fish deaths remains to be seen, and further examination swill be required. Whatever the outcome, the discovery is certain to add to the complications of fish stock management and, if it is spreading, it will add to the burden to the aquaculture economy. The Great Lakes combined have a commercial fishery of some $23 million per year.

While the new virus appears fatal to bass, and perhaps other fish, there is no indication it poses any risk to human health.

The research has been published in the Journal of General Virology. The research paper is headed “Novel reovirus associated with epidemic mortality in wild Largemouth Bass (Micropterus salmoides).”

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