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Gabe Gries: 603-352-9669 
Liza Poinier: 603-271-3211
July 7, 2011

Test Results Show Spofford Lake Fish Kill Likely a Result of Common Aquatic Bacteria

KEENE, N.H. – Test results from fish sampling suggest the recent Spofford Lake fish kill resulted from the presence of a common aquatic bacteria combined with a time of year when fish in the lake were stressed from spawning activity and warm water temperatures. Fish kills occur naturally in N.H. waterbodies from time to time, according to New Hampshire Fish and Game Department biologists, although they typically involve fewer fish. 

The situation began on June 16, 2011, when lakeshore residents of Spofford Lake in Chesterfield noticed unusually large numbers of dead fish floating up on their properties and reported the occurrence to N.H. Fish and Game’s Region 4 Office in Keene.  Residents mainly had observed dead sunfish (bluegill and pumpkinseed), along with smaller numbers of bullhead, northern pike and yellow perch. Fisheries staff visited the lake on June 20 and made similar observations in terms of the mix of species among the dead fish. One bullhead and eight dead sunfish were collected and sent to the U.S. Fish and Wildlife Service (USFWS) Fish Health Center in Lamar, Pa., for testing. During the following two weeks, N.H. Fish and Game fisheries staff continued to visit Spofford Lake every few days to make further observations on the number and species of dead fish. 

“The real peak of the fish kill appeared to be during the week of June 20," said Fisheries Biologist Gabe Gries. "From the end of that week to the present, the numbers of dead fish showing up have steadily declined. We visited the lake again on July 6 and only saw a handful of dead sunfish.”

Test results from the USFWS Fish Health Center were received on July 7 and showed that no virus was present in the fish tested and that the most dominant bacteria found on the test cultures was Aeromonas hydrophila, a common aquatic bacteria. According to Fish Health Center staff, this bacteria only becomes lethal to fish when there is another stressor to the fish. For example, fish that have just finished spawning or that are subjected to rapid increases in water temperature could become stressed to the point where Aeromonas hydrophila could become lethal to the fish.  In some cases, the bacteria can infect a single fish and then multiply rapidly, causing a substantial fish kill.

“Given that the vast majority of dead fish were sunfish, it is likely that sunfish, already stressed from spawning, experienced some warm water conditions that led to the outbreak of the bacteria," said Gries. "Given the low numbers of other fish species found dead, it is difficult to determine if the other fish species died from the bacteria or if they simply were fish that died from natural causes.”

The test results did not raise concerns about eating fish from Spofford Lake. “There is no indication that the bacteria is communicable to humans, but it is, of course, always a good idea to thoroughly cook any fish you wish to eat," said Dr. Richard French of the NH Veterinary Diagnostic Laboratory in Durham, N.H.

NH Fish and Game biologists will continue to monitor the situation at Spofford Lake.  They collected live sunfish and bullhead on July 6 for further testing by the N.H. Veterinary Diagnostic Laboratory.

The New Hampshire Fish and Game Department is the guardian of the state's fish, wildlife and marine resources and their habitats. Visit

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